Discovery of cell – In 1665 Robert Hooke examined thin slices of cork under his self made microscope (Magnification = 42 times). The cork seen was dead bark of spanish oak (Quercus suber). Robert Hook coined the term "Cellula" for Honey comb like structure of bottle cork (Greek cellulae = Hollow space) which later modified to cell. Actually he saw only the dead cell walls of plant cells. He published his findings in his book 'Micrographia'.
R.Virchow stated "Omnis cellula e cellula" which means all cells arises from pre existing cell. This is known as "Law of Lineage".
Karl Nageli showed that cells in plants arises by the division of pre existing cell.
Discovery of living cell by Leeuwenhoek–
Leeuwenhoek examined mud, semen, saliva, blood, Insects etc. Under his self made microscope and observe protozoans, sperm, bacteria, RBC, muscle cells etc.
He called these tiny creatures as "Animalcules" and published his finding in "Secrets of nature”.
He is known as father of microbiology, father of bacteriology, father of protozoology.
Father of cytology is Hertwig & R. Hooke.
Father of modern cytology is C.P. Swannson.
Father of Indian cytology is Dr. A.K. Sharma.
GENERAL FACTS RELATED WITH CELLS
Longest cell is nerve cell of Giraffe. (more than 1m) (90 cm in man).
Largest cell is egg of ostrich (17cm x 13.5 cm dimension).
Smallest cell is PPLO (Pleuro Pneumonia Like Organism).
Smallest plant cell mycoplasma Laidlawii 0.1 .
Centre for cellular and molecular biology is at Hyderabad.
Largest plant cell – Acetabularia (10cm)
Longest plant cell – Remie fibre (Boehmeria nevia)
Schleiden (Botanist) (1838)
Schwann (Zoologist) (1839)
Cell theory was proposed by Schleiden and Schwann.
According to cell theory, all livings things are made up of cells.
Cell is structural and Functional unit of living being.
They has power of Reproduction.
All cells arise from preexisting cells.
All cells are basically similar in structure and metabolic function
Each cell has a unit of heredity
Exceptions to cell theory –
According to this theory all the living organism are made up of cells. Viruses are exception of this theory because virus lacks cell organization.
According to moderm scientists all the acellular organism - monera and protista, Xanthophytes,(Vaucharia) Phycomycetes (Rhizopus) are exception of cell theory.
TYPE OF CELLS
On the basis of nuclear organization, cells are classified into three types [mainly two types] -
Prokaryotic cell G Eukaryotic cell
An intermediate nuclear organization of prokaryotic and eukaryotic cell was given by Dodge. He told that
mesokaryotic cells have well organized nuclear membrane, but their DNA is without histone proteins.
Multicellular organism have three types of cells regarding their capacity to divide and differentiate.
Undifferentiated cells - These are the meristematic cells which possess the power of division, e.g. apical meristem
Differentiated cells - These are post-mitotic specialized cells with a distinct structure and function,
Dedifferentiated cells - These are specialized cells that revert to function of division for wound
healing, regeneration, secondary growth etc.
DIFFERENCE BETWEEN PROKARYOTIC AND EUKARYOTIC CELL
Basis of difference is nucleus.
Term prokaryote and Eukaryote was given by Von Neil.
STRUCTURAL ORGANISATION OF A CELL
Each plant cell is surrounded by a rigid and dead cell wall.
Cell wall was studied at first by Robert Hooke in cork cells.
Due to presence of cell wall plant cell can be differentiated from animal cell
It is secretory substance of the protoplasm which protects the cell
Cell wall present in Bacteria & Fungi (Chemically different)
STRUCTURE OF THE CELL WALL
Generally it is made up of cellulose however the cell wall of fungi is made up of fungul cellulose or chitin and the cell wall of bacteria & BGA is made up of peptidoglycon.
Numerous threads like fibrils are found in the wall
One fibril is formed of about 250 microfibrils (main structural elements)
One microfibril is also formed about 20 to 22 microfibrils which is called elementary Fibril or Micelle.(structural unit)
One micelle is formed about 100 chains of cellulose molecules
Approximately 3000 chains of glucose molecules are found in one molecule of cellulose.
Matrix is found between the microfibrils, this matrix is a gel like substance in which pectin lignin etc
It is formed by division of cytoplasm in two parts at the time of cell division
In this division the minute drops of substances of protoplasm become aligned at the equatorial plate and forms cell plate.
By some physical and chemical changes in this an intercellular amorphous, layer is formed which is called middle lamella.
It is formed of calcium (more) and magnesium (less) pectate (plant cement).
It functions as cementing between two cells.
Protoplasm deposits some substances on the middle lamella due to which a soft, delicate elastic primary wall is formed. (universal layer)
Following substances are found in this wall
Pectic substance (Arabinose, galactose, galacturonic acid)
Hemicellulose (mannose, Xylose, gluconic acid) (50%)
Parenchymatous cells and meristematic cells are formed of only primary wall
Secondary wall (absent in meristem cell)
After the complete development of primary wall, deposition starts due to which secondary wall is formed Generally lignin, cutin and suberin are deposited.
This wall is made up of cellulose, hemicellulose and pectin inside the primary wall.
This wall is non-elastic and thick (5 - 10 )
It is formed of three layers in most of the cells (Thickest wall)
Tertiary wall (mainly hemicellulose & xylan)
After some time cellulose wall is formed on the secondary wall, which is tertiary wall (Inner most).
Tertiary wall and secondary wall is commonly known as secondary thickenings.
Found only in Tracheids of Gymnosperm.
The cytoplasmic bridge between adjacent cells are called Plasmodesmata (discovered by Strassberger).
Plasmodesmata contains E.R. tubules called Desmotubules.
Due to presence of plasmodesmata entire protoplasm are found in the form of continuous system which is called symplast.
THICKENINGS OF CELL WALL
Occur in following pattern –
By Lignification :
The cell wall of xylem (teacheids, vessels & schelerenchyma) and other secondary wall, becomes hard and thick due to deposition of lignin.
Due to increasing amount of lignin deposition the protoplasm is lost and cell becomes less economic importance.
Pits are formed in lignified cell wall. Deposition of lignin occurs thoughout the cell wall leaving some small thin walled areas called pits. Pits are generally formed in pairs on the wall of adjacent cells.
Two pits of a pair are seperated by a thin membrane called pit membrane (completely permeable)
(earliar composed of middle lemella and primary wall) But, after some time primary wall may be dissolve. There are two types of pit pairs.
Simple pits :
If the area of pit is uniform throughout its whole depth , it forms a simple pits.
These pits are abundantly found in thick cell walled parenchyma.
Bordered pits :
When the area is unequal, broader towards the wall and narrower towards the cavity of cell, more or less like a funnel, then it is called bordered pits.
The pit membrane shows a slight thickened swelling in the middle , called torus.
In bordered pits the diffusion is regulated by torus and it functions as a valve.
Suberisation occurs on cork and casparian strips of endodermal cells. Suberin is highly impermeable material. It is water tight and air tight material. So suberisation also leads to death of cell. Maximum suberisation occurs in middle lamella.
Cutin is also hydrophobic, waxy substance. Cutinisation is the deposition of cutin on cell walls of leaf epidermis. It reduces the transpiration rate plants.
Deposition of cutin on the surface of leaf. It leads of formation of cuticle.
Mucilage deposits on the surface of hydrophytes.
Deposition of silica
Occurs on the leaves of grasses, equisetum, atropa, diatoms cell wall, rice.
GROWTH OF CELL WALL
A special protein called expansin helps in growth of cell wall by loosing the cellulose microfibril and addition of new cell wall material takes place in the space. Thus expansin is called as “cell wall
Growth of cell wall takes place by two methods :-
When the particles are deposited between the substance which are already present then this types of
growth is called Intussusception Growth
This types of growth takes place in primary, secondary and tertiary cell wall.
When the layers are desposited on to the layers which are present already , then this types of growth is called apposition growth
This types of growth takes place in secondary cell wall.
Cell wall protects the protoplasm.
Cell wall gives a particular size & shape to cell & functions in form of exoskeleton of cell.
It gives a mechanical support to cell.
Cell wall is permeable so it helps in transport of water & mineral substances
Cell wall plays an important role in absorption, transpiration, transport and secretion etc.
POINTS TO BE REMEMBERED ALWAYS
The middle lamella can be dissolved by strong acid only.
Bacterial cell without cell wall is called Lister-Form.(L-form)
Mucopeptide is a polymer of two amino-sugar, N-acetyl Glucosamine (NAG) and N-acetyl muramic acid (NAM).
In cellulose, a polymer of unbranched chain of glucose molecule linked by -1-4 glycosidic bond.
The cellulose formation is takes place in presence of celulose synthetase enzymes which is present in membrane.
CELL COAT (GLYCOCALYX)
It is found outside the plasma membrane in many protistants and animals cell. Made by sialic acid mucin & Hyluronic acid
It provides definite shape to the cell.
It helps in recognition of microbes for defence.
It protects the underlying plasma membrane.
Term plasma lemma was given by J.Q. Plower (1885).
Term cell membrane or plasma membrane was given by Nagelli.
Term unit membrane was given by Robertson.
At first, structure of cell membrane was studied by Overton and postulated that cell membrane is
composed of a continous layer of lipid material.
It is outermost boundary of animal cell.
Plasma membrane is a thin selective permeable & living membrane.
It is flexible and porus membrane.
Plasmalemma of animal cells is elastic due to the presence of lipids.
MODEL OF CELL MEMBRANE
To describe structure of plasma membrane numerous models have been proposed but the important model are as follow :–
Lipoidal model - This model was proposed by Overton.
Gorter and grandel's lipid Bimolecular model (1925)
This postulated that membranes are composed of Lipid bilayer only.
Lamellar model (PLLP) - (1935) :
This model was proposed by Danielli and Davson.
It is also called trilayered, trilaminar or sandwitch model.
According to this model plasma membrane is a trilayered structure composed of lipoprotein.
The bilayered phospho lipid is sandwitched in between two layer of protein molecule.
The bilayered lipid is 35 Å thick whereas, each layer of protien is 20Å thick so plasma membrane is 75Å thick (75 – 100 Å)
The polar heads of the phospholipids molecules are directed towards protein. The two are held together by electrostatic forces.
The non polar tails of the two lipids layer is directed towards the centre, where they are held together by Vander Walls forces.
Plasma membrane is a porous membrane, it has microscopic pores of 7 to 10 Å.
Unit membrane model [(1959) A.D.]
It was proposed by J. David Robertson
Robertson coined the term unit membrane.
Acco. to this model all the cellular and organeller membranes are structurally & functionally similar
(difference in chemically & size).
Fluidity of the cell membrane
It has been demonstrated by the experiment conducted by Frye and Edidin (1970).
Two different animal cells i.e., human and mouse cells were taken. Human cell was labelled with
red fluorescent (rhodomine dye) antibody, whereas mouse cell was labelled with green fluorescent (fluorescein dye) antibody. Both the cells were then fused using PEG and examined under the microscope. One half of the fused cell was observed green and the other half as red. They are now divided into lots. One lot is kept at 0ºC, while the other is kept at 37ºC. In the lot kept at 37ºC, there is thorough mixing of the two pigments.No mixing occurs in the fused cells kept at 0ºC, where most of membrane lipids tend to solidify. It these cells are now kept at 37ºC, pigment mising occurs showing that membrane or lipid fluidity has been restored.
Fluid mosaic model (1973)
This model was proposed by Singer and Nicholson.
It described protein as ice bergs in a sea of lipids.
It is the most accepted model.
Their is a central bilipid layer (2 layer) composed of phospholipids arranged in a specific manner.
Hydrophilic polar head constitute top and bottom surfaces.
Hydrophobic non polar tail end-are buried in the membrane.
Within phospholipid, bilayer, proteins are arranged in (2) forms
Extrinsic protein (30%)
Such proteins are arranged superficially on the outer and inner surfaces of membrane and can be easily removed by mild treatment.
Such proteins are soluble and unstable.
Such proteins can be seperated by change in pH.
Spectrin, Acetylcholine, Cytochromes are its best example.
Some protein like permeases and translocase function as carrier for the transport of materials.
Spectrin are helical type of extrinsic protein founds on cytosolic face of membrane and attached to intrinsic protein. Spectrins are part of cytoskeleton.
Plasma membrane is an asymmetrical structure because carbohydrate is presents on outer surface and spectrin protein is present
only in inner surface of plasma membrane.
Intrinsic proteins (70%)
Such protein partially or wholly remain embedded in phospholipid.
Such proteins can not be seperated easily.
Some intrinsic protein are confined in lipid bilayer (Stable protein).
Some integral proteins traverse the complete thickness of membrane. These type of protein are called as tunnel protein which passage water soluble material across the membrane.
Some intrinsic protein extending from outside to inside are called as transmembrane protein
eg. glycophorin, porins.
Porins also founds in outer mitochondrial memberane and bacterial memberane
Plasma membrane is composed of protein, lipid and carbohydrate.
Proteins Carbohydrates Lipids
58-60% 1–2% 20–40%
P.M. of human RBC have 52% protein and 40% lipids.
Phospholipid is the main component of cell membrane because it forms continous structural frame of cell membrane. Main type of phospholipids are phosphatidyl serine, phosphatidyl choline (Lecithin),
Phospholipid layer provides fluidity to plasma membrane because phospholipids are rich in unsaturated fatty acid which are liquid in nature.
Cholesterol is also present in plasmamembrane. Cholestrol are more rigid than phospholipid. So it helps in stability of membrane structure at high temperature.
Cholesterol is absent in membrane of prokaryote. Thus Hopanoides (Pentacyclic sterol) provides stability to prokaryotic cell membrane.
Cell (1962) has suggested the presence of carbohydrate in plasma membrane.
The plasma membrane of RBC and liver cell contain 5% carbohydrate Hexasamine sialic acid.
Attach to lipid glycolipid.
Attach to protein glycoprotein.
Carbohydrate is just 1 percent of the plasma membrane.
Oligosaccharides of the glycolipids & glycoproteins on the outer surface of plasma membranes are involved in cell to cell recognition mechanism. Best example of cell recognition is fertilisation, (where sperm & egg recognize to each other) and blood-Antigens.
FLIP-FLOP CONCEPT IN FLUID MOSAIC MODEL :
(Flip Flop means exchange of molecules from one monolayer with those in the monolayer on the otherside).
However phospholipid bilayer has fluid property but no evidence of flip flop mechanism for protein molecule
Rotational diffusion and lateral diffusion of protein and lipids is possible in membrane.
Absence of flip flop movement detected by electro spin resonance (ESR) spectroscopy.
Lomasomes / Border body
Lomasomes are plasmalemma folding found in fungal cell in between cell membrane and cell wall.
Discovered by Moore and Mc Aear.
It is belived that it is related with formation of cell wall.
FUNCTION OF PLASMA MEMBRANE
Plama membrane provide definite shape to the cell.
Conduction of nerve impulse takes place through plasma membrane of nerve cell.
Plasma membrane plays important role in recognition of various cells. e.g. Macrophages engulfes only dead RBC.
The microvilli of intestinal cells increases surface area of absorption so, rate of absorption increase.
The site for cells recognition are located on the surface of plasma membrane.
The antigenic property of a cells are located on the surface of plasma membrane.
Occurs from lower concentration to higher concentration.
During this type of transport, energy is utilized. e.g.- Sodium-pottasium pump.
Occurs from higher concentration to lower concentration.
During this type of transport energy is not utilized.
Movement of ions or molecules from their high concentration to low concentration. If need carrier then called facilitated diffusion.
Osmosis always occurs through semipermeable membrane in which movement of solvent occur.
Osmosis is of 2 types.
It is the process in which water enters from surrounding medium in to the cells.
It is seen when cell is immersed in hypotonic solution.
It is the process in which water goes out of the cell into surrounding medium.
It is seen when cell immersed in hypertonic solution.
It cause plasmolysis.
If RBC is kept in a isotonic solution no osmosis takes place.
If RBC is kept in hypotonic solution RBC Ruptures
If RBC is kept in hypertonic solution RBC becomes flaccid.
Endocytosis (Bulk transport)
Pinocytosis or Cell Drinking - Term proposed by W.H.Lewis (1934). Ingestion of liquid material by plasmalemma in the form of vesicles or bag like structure (Pinosome) is called pinocytosis.
Phagocytosis or Cell eating - Term given by Metchnikoff. Ingestion of solid complex materials by Membranes in the form of vesicles (Phagosome) is called Phagocytosis.
Exocytosis / Emiocytosis / Cell vomitting - Egestion of waste materials from cell through plasma membrane.
This is transfer of complex materials from one cell to another cell, through membrane in vescicular form.
(Transfer of Hb from Red Bone marow cells to maturing RBCs is good example of Rophaocytosis).
POINTS TO BE REMEMBERED ALWAYS
Cholestrol becomes intercataled between phospholipid in membranes and increases the stability of the bilayers and prevents the loss of membrane liquidity at low temprature.
The lipid act as a barrier to the entry or exit of charged polar substance.
Faciliatated diffusion occurs through the agency of special membrane protein called Permeases but
like simple diffusion, it does not requires metabolic energy.
Plasmolysis can be shown only by living cells. So, it can determine whether a cell is living or dead.
Mass of protoplasm lying in between outside of nucleus and plasma membrane is called cytoplasm.
(term - strassberger)
It is colourless homogenous, translucent, amorphous and colloidal fluid.
The peripheral part of cytoplasm is normally non-granular and clear and known as ectoplasm.
The inner portion is granular and less viscous known as endoplasm.
Ground plasm / Hyaloplasm / Cytosol Liquid matrix of cytoplasm except organelles.
Trophoplasm Part of cytoplasm containing organelles & non living inclusions.
Cell inclusions are non -living matter.
Cell organelles are organised structure of cytoplasm capable of growth and in some cases multiplication.
Double membranous structure
Nucleus, Mitochondria and Plastids.
Single membranous structure
Lysosomes ,Microbodies, Golgi complex and Endoplasmic reticulum.
Non membranous structures
Ribosome and centriole.
Power house of cell or ATP-mill in cell.
Cell within cell / second largest organelle
Cell furanaces or storage batteries.
Most busy and active organelle in cell
Semi autonomous cell organelle.
It was discovered by Kolliker 1880. (In straited muscles of insect)
It was named bioplast by Altman in 1886.
It was named mitochondria by C. Benda.
C. Benda stained it with crystal voilet.
Mitochondria is present in immature RBC. It occur in all cells except RBC and prokaryotes.
In prokaryotes the respiratory enzyme are present on the cell membrane instead of
Mitochondria are distributed through out the cytoplasm and are localised at the sites engaged in higher
It also found at the base of cilia to provide energy for movement.
It also found in the light band of muscle to provide energy for contraction.
The cell in which energy requirement is high possess large numbers of mitochondria.
Microsterias and Tripanosoma & Chlorella (Algae) - One
Yeast - Less than 10.
Liver cells - 500
Kidney 300 to 400
Chaos chaos (amoeba) - (5 lakh).
Number of mitochondria is highest in flight muscles of Birds. (sarcosome)
Generally in plant cell number of mitocondria is less, incomparison to animal cell.
SHAPE AND SIZE
Mitochondria may be spiral, rod shaped, spherical elongated or cup shaped.
Yeast cell possess smallest mitochondria (0.1 ).
Oocytes of amphibians possess largest mitochondria (40 ).
Mitochondria is covered by double unit membrane. Outer membrane has more phospholipids (Phosphatidyl choline) and cholesterol as compared to inner membrane. Phospholipid in inner membrane is mainly diphosphatidyl glycerol and inner membrane have more protein.
Each membrane is 60-75 Å thick and separated by a space (80 - 100 Å) called perimitochondrial space. This space is rich in coenzymes and enzymes required for oxidation of fats.
If outer membrane of mitochondria is removed then structure is called as mitoplast.
Outer surface of inner membrane is called C-face while inner surface called M-face.
Some sessile particles attached to outer membrane are known as “subunit of parsons”
It is projected into the central space in the form of finger like projections called cristae-cristae name was given by palade..
the cristae increase the surface area and provide abundant space for metabolism.
Inner membrane is selectively permeable.
It contains all enzymes of electron transport chain.
Elementary particles or oxysome or F1–particles
F1 particles was at first described by Fernandez moran.
It contain enzyme of electron transport system and oxidative phosphorylation.
It differentiated into base, stalk and head.
A mitochondria may contain 104–105 particle.
The head piece (f1) is associated with ATP synthesis by enzyme ATPase
Base (Multiprotein complex)
It is also called F0 subunit.
It is embedded in inner mitochondrial membrane.
F0 subunit is also called oligomycin sensitivity conferring protiens (OSCP). (It provide tunnel for
Mitochondrial matrix have enzyme for kreb’s cycle. Beside these enzymes matrix have a complete
protein synthesis apparatus (Ribosome (70-s), DNA & RNA, enzyme)
Mitocondrial DNA was discovered by Nash and Margit in 1963.
One to many (6kb to 36kb long) double stranded mainly circular naked DNA is present is mitochondrial
Mitochondrial DNA is 1% of total DNA is a cell. It is rich is G-C content
Enzymes for replication and transcription of DNA like DNA-polymerase and RNA-polymerase are found
in Mitochondrial matrix.
Mitochondria of mammals have 55 s ribosomes (35s, 25s units)
FUNCTION OF MITOCHONDRIA
Mitochodria is site for cellular respiration because it contains all enzymes required for it.
Since mitochondria is a site of cellular respiration energy, (ATP) is formed in it.
Mitochondria help in yolk formation during the development of ovum. (vitellogenesis)
Mitochondria help in formation of middle piece of sperm during sperm maturation. (spiral sheath)
Mitochondria help in elongation of fatty acids.
MITOCHONDRIA AS SEMI AUTONOMOUS ORGANELLES
Altman stated mitochondria as semiautonomous organelle.
The mitochondria DNA carries enough information for the synthesis of about 30 proteins only but that
is not enough to make a new mitochondria, so the mitochondria depend upon the nuclear DNA.
Cytoplasmic enzyme and other molecules of the cell, using all the machinery mitochondria replicates,
during cell division.
Mitochondrial DNA produces its own m-RNA, t-RNA and r-RNA.
Biogenesis of mitochondria
Endosymbiotic origin from Purple Sulphur bacteria or prokaryotic cells, because mitochondria are similar to prokaryotic cell in -
Structure of DNA and DNA sequences
Type of ribosomes (70s).
Sensitivity of Antibiotic chloremphenicol with protein synthesis.
Divide by amitosis or fission
In scurvy disease numerous mitocondria combine with each other and from large lobe called condriosphere
First all the term plastid was coined by Haeckel.
It was discovered by Schimper in 1883.
Plastids are found in all plant cells except bacteria, fungi and blue green algae.
It may be colourless or coloured and get converted from one form of plastid to another. [Chromoplast
to Chloroplast never occur]
On the basis of colour these are following two types –
(CLeoulocuorp lleassst) (Store food mainly)
Amyloplast Protinoplast Elaioplast
Green C|oloured Chloroplast –– XC aa nr|othteonpehyll –– PPhhyyrcooceyraytnhinrin
Non green Chromoplast
These are colourless and irregular in shape.
These are found in those cells in which light is not available e.g. under ground stem and root
These are found in parenchymatous cells, sex cells, embryonic and meristematic cells.
On the basis of storage of food leucoplast are divided in the following three types :
These are of large size and store starch.
These are found in root, seed and stem.
Protienoplast (Aleuronoplast) :
They store proteins and are found in seeds (pulses).
They store fats & oil and are found in seeds. They are also called olleosome. [castor, groundnut]
These are plastids without pigments, stored food and lamellar structures. These plastids occur in etiolated
plants due to the absence of light
Chromoplast is found in fruits and flower.
They exhibits red, orange and red yellow colour.
Chromoplasts also occurs in petals but colour of petals are mainly due to water soluble pigments occurs in cell sap. e.g. Anthocyanin - (Blue or violet or red pigment) Anthoclor (yellow pigment Beta cyanin - Beetroot)
Chromoplast contains following types of pigments –
It is of orange , red or yellow colour
Due to soluble in fats these are called lipochrome.
These are found in all parts of plants and for its synthesis light is not necessary.
It is of following two types –
Carotene : Redcolour of chillies and red tomatoes is due to the red pigment “Lycopene” of
chromoplasts. Yellowish - orange colour of fruits are due to -carotene, -carotene and -carotene.
-carotene is precursor of vitamin-A. Richest source of -carotene are carrot roots.
These yellow coloured carotenoids are also called Xanthols. Fucoxanthin is found in brown
algae which provides brown colour to algae.
Water soluble in nature.
These are of following three and found in blue green & red algae.
Chromatophores - These are clusters of pigment granules in cytoplasm of photosynthetic bacteria.
In blue-green algae pigments are located on membranous lameller structures, scattered in Cytoplasm.
These structures are known as chlorosomes or Lamellisomes or Carboxysomes.
First of all Mayer seen it in plant cell and named Autoplast.
Schimper discovered it and term chloroplastid was given.
Chloroplast name was given by Errera
Due to presence of chlorophyll in these plastids leaves and parts of plants exhibits green colour.
These are found in the mesophyll of leaves and chlorenchyma region of higher plants.
Their size & shape varies in different plant groups
In higher plants (e.g Mosses, Fern and Seed plants) they are flat, circular, oval and elliptical
In lower plants (e.g. Algae) they are as followings :
Cup shaped – Chlamydomonas
Girdle shaped – Ulothrix
Spiral shaped – Spirogyra
Reticulate shaped – Oedogonium
Stellate shaped – Zygnema
Chloroplast has an envelope composed of two unit membranes
Blank space is found between unit membrane which is called periplastidial space.
In this bilayered membrane bounded structures, the proteinaceous matrix is found, which is called stroma.
Stroma contains a variety of particles, osmiophilic droplets, Strands of RNA and DNA (ds, circular, naked) Ribosomes, Enzymes and Dissolved salts.
Due to presence of DNA & RNA chloroplast is known as Semiautonomous organelle and Cell within cell
Rubisco is the most abundant enzyme on the earth. It made 16% protein of the chloroplast.
In the stroma many membranes which are running parallel to each other throughout the length of the chloroplast, called Thylakoid lamellae.
Thylakoid Lamellae have some rounded flat, sac-like structures stalked one above the other, these
structures are called Granum thylakoid.
Thylakoid was discovered by Menke.
The group of granum thylakoids is called grana (plural), different grana are connected with the help of tubular connections called Frets or Intergranum.
A photosynthetic functional unit, which consists of about 230 to 400 molecules of various pigment (Chla,Chl-b, carotenes, xanthophylls etc.) is called as Quantasomes (By Park & Biggins 1964).
MAIN PIGMENT OF CHLOROPLAST
It was discovered by Pelletier & Caventou.
The following types of chlorophylls are found in plants -
This chlorophyll is found in all photosynthetic organism except photosynthetic bacteria, so it is also called as universal chlorophyll.
This chlorophyll is found in all higher plants and in green algae but not present in algae of other group.
It is found in brown algae (Phaeophyceae) and diatoms.
It is found in red algae (Rhodophyceae).
It is found in Xanthophyceae e.g. Vaucheria.
Bacteriochlorophyll - a
It is found in photosynthetic bacteria
Bacteriochlorophyll ‘b’ : It is found in Rhodopseudomonas
Chlorobium chlorophyll : It is found in green sulphur bacteria
Chloroplasts are self duplicating organelles. New chloroplasts arise by the division of pre-existing ones, or from proplastids.
The chloroplasts perform various functions like;
Photosynthesis - light reaction (in thylakoids), Dark reaction (in stroma)
The main function of chloroplast is photosynthesis, in which radiant energy of sun is converted into chemical form of energy, which is utilized by all kliving organism to perform their life activities. Further, chloroplasts help in maintaining balance of O2 and CO2 in the atmosphere.
Storage of starch, vitamin K, E, Rubisco protein and iron etc.
Endoplasmic reticulum was discovered by Porter in 1945.
It was first of all observed under light microscope by Garnier in 1897.
The term E.R. was first of all used by Porter.
It was named ergastoplasm by Garnier.
Robertson described relationship inbetween endoplasmic reticulum and plasma membrane.
It is absent in Prokaryotes, present in all eukaryotes except germinal cells and mature mammalian erythrocytes.
It is found scattered in whole cytoplasm.
Structure of E.R. is like the golgi body but in E.R. cisternae, vesicles and tubules are isolated in
cytoplasm and these do not form complex
Golgi body is localised cell organelle while E.R. is widespread in cytoplasm. E.R. is often termed as
“System of membranes”
Endoplasmic reticulum is network of highly branched fine tubules.
Its one end, is connected with nuclear membrane whereas other end with plasma membrane.
It is composed of three types of forms which are as follows.
Cisternae Vesicles Tubules
It is elongated flattened, unbranched tubular structure which are found arranged in parallel rows.
It is generally granular due to presence of ribosome.
It is mainly found in cells actively indulged in protein synthesis like in liver, pancreas etc.
It is rounded oval form of 25-500 micron.
It is found well scattered in the cytoplasm.
It is mainly found in protien forming cells.
It is also granular structure.
It is tubular, highly branched, found near the cells membrane.
It is smooth structure, because ribosome is absent from its surface.
It is mainly found in cells associated with synthesis of cholesterol, glycerides, hormones etc.
TYPES OF E.R.
SER - In Smooth endoplasmic reticulum ribosome is not found.
RER - In Rough endoplasmic reticulum ribosomes is found on the surface of ER.
Ribosome are attached to ER by a glycoprotein called ribophorin-I & II
SER of pigmented epithelial cells of retina is called myeloid body.
RER of nerve cells is called nissle's granules (Ergastoplasm)
SER get originated from RER by loss of ribosome.
RER arises by evagination of outer nuclear membrane.
E.R is composed of lipoprotein.
Protein constitute 60 % whereas lipids 40%.
These smooth E.R. occurs in skeletal and cardiac muscles. S.E.R. Stores Ca+2 and energy rich compounds required for muscle contraction.
T-tubules - these are transversely arranged tubules in skeletal and cardiac muscle cells. These transmits stimulus for contraction of muscls.
Microsomes are fragments of E.R. associated with ribosome.
It was was first discovered by Claude in 1951.
It is obtained by high speed centrifugation.
E.R. acts as cytoskeleton and provide mechanical support and shape to the cell.
E.R. helps in the formation of primary lysosome, Golgi body, microbodies etc.
E.R. also helps in synthesis of nuclear envelope during telophase.
It helps in lipid synthesis.(Phospholipid & Cholestrol)
It helps in synthesis of steroid hormone.
It helps in glycogenolysis. (glycogen glucose)
It helps in synthesis of ascorbic acid.
Intracellular exchange - E.R. forms intracellular conducting system. Transport of materials in cytoplasm
from one place to another may occurs through the E.R.
Cellular metabolism - The membranes of the reticulum provides an increased surface for metabolic
activitities within the cytoplasm.
Detoxification - Smooth ER concerned with detoxification of drugs, pollutants and steroids.
Cytochrome P450 in E.R. act as enzyme which function in detoxification of drugs and other toxins.
It provides the precursor of secretory material to golgi body.
It is also called as lipochondrian, Dalton complex, idiosome, Baker's body, golgi body. In plant cell it is also called dictyosome.
It was at first observed by George in 1867 A.D.
It was discovered by Camilo golgi in nerve cells of owl and cats.
Baker at first stained it with Sudan black reticular apparatus.
All the macromolecules which are to be sent out side the cell, move through the golgi body. So golgi
body is termed as “Principal director of macromolecular traffic in cell” or middle men of cell.
It is absent in prokaryotic cells.
Absent in mature RBC and sperm
Found in large number in secretory and glandular cells.
The cytoplasm surrounding Golgi body have fewer or no other organelles. It is called Golgi ground substance or zone of exclusion.
Golgi bodies are pleomorphic structures because component of golgi body are differ in structure & shape in different cells.
Structure of golgi complex described in detail by Dalton and Felix.
In golgi body 4 types of structure is found which are as follows.
Cisternae G Vesicles G Vacuole G Tubules
It is also flattened sac, saccules or parallel membrane.
It is elongated and unbranched tubules.
It is curved structure with swollen ends present one upon the other.
The curved convex structure is directed towards nucleus(cis-face / forming face), whereas (maturing face / trans face) is directed towards plasma membrane.
The functional unit of golgi apparatus is cisternae.
Vacuole Cisternea Intercisternal space
It is numerous droplet like structure.
They are found around convex surface or edges of cisternae.
It is formed by budding from cisternae. Filled with secretory materials.
It is large round structure found around concave or edges of cisternae.
These are branched and irregular tube like structure associated with cisternae.
It is composed of lipoprotein.
Protein is 60% whreas lipid is 40%.
Golgi body originated from ER.
Cell Secretion - Cheif function of golgi body is secretion (export) of macromolecules. Secretion involve three stepes
Golgi body recieve the materials from E.R. through its cis-face.
Materials are chemically modified by golgi body. (For e.g. Glycosidation (Glycosylation) of proteins and lipids takes place in golgi body and it yields glycoprotiens and glycolipids).
After chamical modification materials are packed in vesicles. These vesicles are pinched of from trans face of golgi body and discharged out side the cell (Reverse pinocytosis).
During spermatogenesis it forms Acrosome of sperm.
Lysosome get formed from it.
It is helpful in synthesis and storage of yolk & vitelline membrane of egg.
It is helpful in synthesis of melanin pigment.
In plant cell it forms cell plate (phragmoplast).
It stimulate mitochondria for the production of ATP.
It helps in synthesis of carbohydrate. Mainly polysaccaride (cell wall material).
Secretion of Zymogen from Pancrease. Lactoprotein from mammary glands & Hormones.
Mucilage secretion by root cells.
Secretion of hormone by endocrine glands is mediated through golgibody.
Lysosome is also called sucidal bags.
It was discovered by Christan De Duve (1955) accidently when he was working on rat liver cell to
isolate certain enzyme. P.Matile (1964) reported in plant cells.
In begening it was named paracanalicular bodies.
First observed by Novikoff.
It is absent in prokaryotic cells, RBC and sperm.
These are found in abundant in Phagocytic and secreted cells like WBC, Kuffer's cells, pancreatic cells, liver cells & Fungi.
In 1973 Pit and Galpin discovered its presence in higher plants. In majority of higher plants large food
vacuole act as a lysosome.
In bacteria space in between cell wall and cell membrane act as a lysosome. (periplasmic space)
Lysosome shows polymorphism (Different morphological and physiological stages).
It is round, sac like structure bounded by single unit membrane composed of lipoprotein.
It is filled with granular matrix. In matrix nearly 50 acid hydrolases is found which are digestive enzyme.
Acid hydrolases are capable of hydrolysing all classes of macromolecules.
Following are the important acid hydrolases found in lysosome.
S.No. Enzyme Substrate
(i) Nuclease Nucleic acid.
(ii) Protease Protein.
(iii) Glycosidase Polysaccharides.
(iv) Lipase Lipids.
(v) Phosphatase Phosphate linked compounds.
(vi) Sulphatase Sulphate linked bonds
All enzymes found in lysosome requires acid for their action, hence called acid hydrolases.
These acid hydrolases function at pH-5. Membrane of lysosome has an active H+ pump mechanism which produce acidic pH in lumen of lysosome.
Lysosome get originated from :–
Plasma membrane by the process of pinocytosis or phagocytosis.
Biogenesis of Lysosome - system of GERL - (Golgi Associated Endoplasmic Reticulum) from which
Lysosome attains four different form so it is called polymorphic organelle. The four forms are as
Primary Lysosome (Protolysosome) / Storage
The primary lysosome or prelysosome are small sac like bodies.
These are secreted directly by endoplasmic reticulum and cisterne of golgi complex and get filled with inactive enzyme.
Secondary lysosome (Heterophagosome or digestive vacuoles)
When the primary lysosome fuses with the other vacuoles (pinosome / phagosome) it is called secondary
In it active enzymes are found.
It is also called phagolysosome.
Residual body / Tertiary Lysosome
Secondary lysosome + Undigested food = Residual body.
After the products of digestion have been absorbed in to the cytoplasm. The undigested remains are left in the lysosome, it is called residual body.
This moves to the surface and throws the contents by exocytosis.
It is also called telolysosome.
Autophagic Lysosome (Autophagosomes or cytolysosomes)
This type of lysosome, contain part of its own cells (Generally unwanted structure) and digest it
It is a part of the normal activity by which old organ cells are digested and new ones are formed.
It occurs more frequently during differentiation.
Intracellar digestion / Heterophagy - Lysosome digests substance which enter within a cell by
phagocytosis and pinocytosis.
Extracellular digestion - Lysosomes of osteoclast (bone eating cells) dissolve unwanted part of bones. (Extracellular digestion also occurs by fungal lysosomes)
Autophagy - Lysosome digest old and damaged cell, during this process, lysosome get brust, and enzyme enclosed within lysosome get released. This mechanism is called autolysis. (starvation) Unwanted organs of embryo are destroyed by autolysis, Cathepsin of lysosome digests the tail tadpole of frog during metamorphosis.
Lysosome help in digestion of harmful substance WBC digest bacteria, germs, viruses and help to give defence to the body.
Lysosome help in dissolving the egg membrane, during fertilization.
Crinophagy - Excessive secretory granules of hormone in endocrine gland may be digested by lysosomes. This event is called crinophagy. Thyroglobin stores in thyroid gland with in its follicles and after crinophagy by proteases it produces thyroxine.
POINTS TO BE REMEMBERED ALWAYS
The membrane of lysosome shows controlled permeability.
Labilizers : The chemicals which brings about instability in the permeability characters are called labilizers. eg. Vitamin A, Vitamin D, , Vitamin-E, Vitamin K, ubiquinone, digitonin, progestron, testosterone etc. In presence of these chemicals lysosomal membrane become fragile.
Stabilizers : Few other chemicals brings about stability in the permeability characters of lysosomal
membrane where are called stabilizers. Eg. chlolesterol, cortisone, cortisol, heparin, chloroquinine.
The release of lysosomel enzymes occur under extremes of pH and critical levels of Ag++, Hg++ and Cu++.
Ribosome was discovered & term by Palade
Ribosome was at first seen by Claude in electron microscope in animal cell.
Ribosome was discovered by Robinson and Brown in plant cell of bean roots.
Ribosome are without any membrane.
Ribosomes are the smallest and largest in number organelles in a cell.
Ribosome are also called as “Organelle with in an organelle” & “Protein factory of cell”.
Ribosome are small organelles found in all types of cells. (except mature mammal RBC)
In prokaryotes ribosomes are attached with plasma membrane and some are scattered in the cytoplasm, because no ER is found.
In eukaryotes ribosomes are scattered in the cytoplasm and attached to endoplamic reticulum and outer nuclear membrane.
They are found in large number in protein synthesizing cells.
ULTRASTRUCTURE OF RIBOSOME
Each rirosome composed of two subunits i.e. larger and smaller subunits. Larger subunit is dome shaped and smaller unit is ovoid.
Smaller subunit has a platform, a cleft & head. The larger subunit has a protuberance, a ridge and a stalk.
Larger subunit also contains a tunnel which opens in cavity of E.R.
80s = 60s + 40s
70s = 50s + 30s
Magnesium ion is essential for the binding the ribosome sub units.
Mg+2 form ionic bond with phosphate groupsof r–RNA of two subunits.
Minimum 0.001 M Mg+2 concentration is required for structural formation of ribosomes.
If Mg+2 concentration increased 10 times then ribosome dimer are formed.
Ribosome is mainly of two types, which are as follows –
Prokaryotic Ribosome (60% RNA + 40% protein)
Prokaryotic ribosome is 70S.
70S ribosome have two subunits 50S and 30S.
It is larger subunit.
Its base is spherical.
RNA found is 23'S rRNA and 5S rRNA.
Note : S = Swedberg unit or Sedimentation rate.
It is small subunit.
Its base is rod like.
RNA found is 16S rRNA.
Eukaryotic ribosomes (40% RNA + 60% Protein)
It is 80s ribosomes.
It is composed of 60S and 40S subunits.
It is larger subunit.
It contain 28S, 5S, 5.8S rRNA.
Larger subunit contains Peptidyl transferase enzyme which helps in the formation of peptide bond during protein synthesis. This is an example of Ribozyme. (Noller 1992)
Two sites are found on larger sub units :
A-site Acceptor site for t-RNA
P-site site for growing polypeptide chain
It is smaller subunit.
It contain 18S rRNA.
POLYRIBOSOMES OR POLYSOME
At the time of protein synthesis-
Two subunits of ribosomes get attached.
Many ribosomes get attached with mRNA and known as polyribosome or polysome.
Larger subunit of ribosome get attached with - ER through ribophorine-I & II.
Smaller subunits of ribosome get attached with -mRNA.
CHEMICAL COMPOSITION OF RIBOSOME
It is composed of RNA and Protein (Ribonucleoprotein).
55 s ribosome in mitochondria of mammal.
BIOGENESIS OF RIBOSOME
In prokaryotes ribosome originate in cytoplasm.
In eukaryotes ribosome originates in nucleolus. There fore nucleolus is also called as ribosomal
factory. After synthesis move to cytoplasm where protein synthesis occur.
The proper folding and transport of proteins is assisted by specific proteins called chaperons.
Main function of ribosome is protein synthesis so called protein factory or cell engine.
Centrosome was discovered by Benden. Boveri named as centrosome. Centrosome is absent in higher plants.
Two centrioles located just outside the nucleus and lie at right angle (90º) to each other. Cytoplasm which surrounded centrioles called as “Centrosphere”. Centrioles and centrosphere collectively called centrosome or Microcentrum or diplosome.
Each centriole is surrounded by peri centriolar mass, which is called as massules or crown or satellite.
Centrioles are membraneless elongated structure which exhibit cart wheel structure (Just like Basal bodyof cilia). Basal body is also a type of centriole.
Centriole mainly consist of 9 triplet fibers of tubulin. (9 + 0 arrangement).
Centrioles are self duplicating units, which contains DNA, RNA and protein synthesis machinery.
Centriolar DNA discovered by Randall and Disprey. Centriolar DNA is probably ds circular and naked.
Replication of centriole occur in s-phase.
Function : - In animal cells centroiles play important role in initiation of cell division by arranging spindle fibres between two poles of cell.
The location of centrioles during cell division decides the plane of division. The plane of division is always at right angle to the long axis of spindle. Thus centrioles is also termed as “cell centers”.
CILIA AND FLAGELLA
Cilia and Flagella are Mechanical, hair like cellular appendages and locomotory structure. Flagellar apparatus is consist of following Parts.
Kinetosome or basal granule or Blepheroplast or Basal body : It is membraneless structure lies immediately below the plasmamembrane. Basal body exhibit cart wheel structure similar to centriole. (9 triplet fibriles connected to a central hub in basal body.)
Arrangement of microtubules is 9 (triple) + 0. In basal granule there occurs 9 microtubules on periphery and each microtubule is composed of three tubules i.e. A-tubule, B-tubule and C-tubule.
Central part of basal granule is composed of semisolid cytosol called “Central Hub.”
Microtubules connected to central Hub with the help of protein fibers called Primary fibers or spokes.
Secondary fibers connect microtubules with each other.
Each primary fiber have a thickening called X-thickening. In between X-thickenings there occurs Y-thickenings,
X and Y-thickening are inter connected.
Rootlet Rhizoplast : This is a conical bundle of protein fibers which arises from basal body to different directions.
Rootlet have dark bands composed of ATPase.
Shaft or Ciliary part : It is projecting hair like part of ciliary apparatus. Cilium is composed of 11 microtubules.
(9 doublet + 2 singlet)
Bundle of microtubules is called as axonema. Nine microtubules are peripheral and each composed of two
small tubules i.e. A tubule with two arms and B-Tubules without arms.
Microtubules is consists of a contractile protein tubulin similar to actin of muscles.
Arms of A tubules consist of an enzymatic protein dynien similar to myosin of muscle cells. Dynien have
ability of hydrolysis of ATP & liberates energy for ciliary movement.
The central tubules are connected by bridges and is also enclosed by a central sheath, which is
connected to one of the tubules of each peripheral doublets by radial spoke. Thus there are nine radial
spokes. The peripheral doublets are also interconnected by linkers.
Type of Flagella :
Whiplash - When the lateral hair like structures absent.
Tinsel - When the flagella bears lateral hairs like structure (Flimmers)
Cilia and Flagella are similar in structure but some differences may observed-
Discovered by Spallanzani
Vacuoles are generally absent in animal cells and meristematic cells in plants. Cell of permanent tissue in plants have well developed vacuoles.
Vacuoles are surrounded by an unit membrane called tonoplast. Inside vacuole there is a nonliving fluid called cell sap.
Cell sap contains water, salts, sugars, organic acids, Vitamins and waste materials of metabolism.
Sometimes call sap have certain water soluble pigments like anthocyanin (blue or violot), anthoclor (yellow) etc. Beta cyanin in
Microbodies are single membrane bound small spherical structures. Size vary from 0.3 – 1.5 μm
It includes following :–
PEROXISOMES OR URICOSOMES
Discovered by Rhodin and Tolbert.
In animal cells, peroxisomes are concerned with Peroxide Metabolism.
Peroxisomes contain several enzymes like urate oxidase, amino acid oxidase, peroxidase which catalyze the oxidation of substrates forming H2O2 (Hydrogen peroxide).
H2O2 formed is highly toxic hence it is acted by another enzyme found in peroxisome i.e. Catalase which quickly degrades H2O2 into water & oxygen.
Catalase is the fastest acting enzyme known after corbonic anhydrase& it is a marker enzyme of peroxisomes.
Peroxisomes are also involved in –oxidation of fatty acids.
In plants, they occur in cells of green tissue and are concerned with photorespiration (glycolate pathway)
Hanstein (1880) discovered them & named microsomes.
Perner (1953) gave the name 'spherosome'.
They occur in plant cells only.
They are major site for lipid storage and synthesis.
Cutin & Suberin are synthesized in it.
Discovered by, Beever in oil containing seeds, yeast cells, guard cells etc.
Glyoxysomes occur only in plants especially in fatty seeds (castor seed), guard cells of stomata and unripe fruits.
Glyoxysomes are considered as a highly specialised peroxisomes. Glyoxylic acid cycle takes place in glyoxysomes.
This cycle convert fats into carbohydrates (Gluconeogenesis).
Special microbodies in ovary cells of birds (concern with yolk formation). These covered by three unit membranes.
Microtubules are present in eukaryotic cell.
The wall is made up of helically arranged polymer chain of protein tubulin.
Microtubules are seen in cilia and flagella, centriole & cytoplasm.
They form a cytoskeleton and are responsible for maintaining the shape of the cell.
They radiate from the centrosphere around centriole and form spindle fibre.
They form the cytoskeleton of cillia and flagella.
They are involved in the sliding motion of chromosome during cell division.
In plants microtubules often found associated with cell wall. Probably these transport cell wall material from Golgi body to outside of cell.
Microfilaments are long rods 40-50Å in thickness and distributed through the cytoplasm. They are composed of contractile protein, Actin which concern with muscle contraction and cyclosis. Microtubules and microfilament provides cytoskeleton-base of cell.
The cell inclusions contain both organic storage materials and inorganic crystals. Cell inclusions are nonliving and temporary structures of cytoplasm called “Paraplasm” or “Metaplasm” or “Deutoplasm”.
These includes excretory materials (waste products), stored food and secretory materials.
They are found in plant cell only.
They are stored in Rhizome, potato, tuber, rice and maize.
The starch grain may have concentric or acentric ring of starch around hilum made of protein.
They occur in fat storing cell and are found in adipocytes of animal.
In plants they are mainly found in seed, dry fruits endosperm of caster, coconut and in cells of cotyledons of ground nut.
Stored protein are found in the form of aleurone grain of cereals.
They are complex polysaccharide.
They are stored in the muscle cell of animal.
Cystolith (Grapes cluster)
This is the deposition of calcium carbonate found in epidermis cell of ficus leaves.
The cell containing cystolith is called a lithocyst, also, occur in the cell of cucurbitaceae, ficus, Hevea, Juticia.
Calcium oxalate -
Two types of Crystals
Raphides - needle like crystals which occur solitary or in groups eg. Eichornia, Pistia, rubber plant.
Spheroraphides or Drus or congulomerate crytals, these are star like crystals of calcium oxalate.
eg. Colocasia, Pistia, Carica papaya (Papaya), Atropa, nerium, Dioscorea
Silica - cell wall in grasses and Equisetum impregnated with silica, Silica particles also occur in cytoplasm of Atropa Belladona leaves and roots.
Alkaloids - Nitrogenous waste materials, bitter in taste and insoluble in water. Alkaloids are of great
Glycosides - Nitrogen containing degradation products of carbohydrates e.g. Digitoxin obtained from
leaves of Fox glove (Digitalis purpurea). Digitoxin is used as heart stimulant.
Tannins - Derivatives of glycosides, soluble in water. Tannins are bitter in taste. These occur more in
unripe fruits. Tea leaves have 18% tannins, kattha obtained from heart wood of Acacia catechu have
high concentration of tannins.
Potato Wheat Banana Rice Pea
nucleus is very important and largest component of cells.
Generally eukaryotic cell contain at least one nucleus but nucleus is absent in mature phloem sieve tube elements and mature RBCs of mammals. (exceptionly nucleus is present in RBCs of camal & lama).
Dikaryotic (Paramecium) and multikaryotic cells are also known. Multinucleated cells may be following
Coenocytic cells : This type of cells, are formed by free nuclear division.
Example : Phycomycetes fungi, Endosperm, rhizopus, vaucheria, etc.
Syncytium : Syncytial condition is formed by the fusion of cells.
Example : Epidermis of nematods, Striped muscles.
STRUCTURE OF NUCLEUS
Nuclear membrane :- Nucleus is surrounded by two unit membranes, thus nucleus is double membranous component of cell. Space (150 to 300Å) between two membranes is known as perinuclear space. Outer membrane, of nucleus may connected with E.R. at several places and ribosome also may found on it.
Nuclear membrane is perforated by minute nuclear pores of size, 300 to 1000Å diameter. Each nuclear pore is guarded by a octagonal discoid structure of nucleoplasmin protein this structure is called as annulus or Bleb. (Annulus + Pore = Nuclear Pore complex).
Nuclear pore mainly regulates :-
Proteins moving into the nucleus to be incorporated into nulear structure or to catalyse nuclear activities.
RNA & protein-RNA complexes formed in nucleus and exported to cytoplasm.
The inner side of inner nuclear membrane is lined by nuclear lamina. This structure is formed by filaments of lamin protein.
Pore complex provides the main channel, between nucleoplasm and cytoplasm, while nucleoplasmin regulates nucleocytoplasmic traffic.
Nucleoplasm or Karyolymph :- (Term by Strasburger 1882)
Nucleoplasm or Nuclear sap is a ground substance of nucleus which is a complex colloidal formed of a number of chemicals like nucleotides, nucleosides, ATPs, proteins and enzymes of RNA and DNA polymerases, endonucleases, minerals, (Ca++, Mg++) etc.Nucleoplasm contain high concentration of Nucelotides in the form of triphosphate.
Nucleoplasm also have enzymes for Glycolysis, thus nucleus may obtain energy by glycolysis.
Chromatin net and nucleolus are embeded in nucleoplasm. Nucleoplasm provides site for process of transcription.
Chromatin net : - (Term given by Flemming)
It is an intranuclear, (stained with basic dyes) long, thread like fine fibers, which embeded in nucleoplasm.
Chromatin net is mainly formed of DNA and histone protein complexes. Chromatin fibres contain genetic information and
condensed to form constant number of chromosomes during cell division.
Chemically chromatin consists of DNA (31%), RNA (2-5%), Histone protein (36%) and non histone protein (28%). On the basis of relative amount of arginine and lysin there are five type of Histone
protein. (H2A, H2B, H3,H4, H1)
Chromatin net has two type of chromatins (by Emil Heitz)
Euchromatin :- This is lightly stained and diffused part of chromatin. Which is transcriptionally or
genetically more active. Generally euchromatin lies at central part of nucleus.
Heterochromatin :- This is a dark stained, thick and condensed part of chromatin this part have more histone and less acidic protein. Heterochromatin is genetically less active chromatin and forms stop point in transcription. Heterochromatin occurs near nuclear membrane.
Constitutive heterochromatin :- Occurs in all cells in all stages e.g. centromeric region.
Facultative heterochromatin :- Occurs in some cells in some stages. e.g., Barr body.
Barr body in female cell is a facultative heterochromatic structure. (By M.Barr)
Number of Barr body in nucleus of an individual is number of (X-chromosome) minus one.
Heterochromatin takes light stain during cell division stages (M-phase) & takes dark stain during interphase.
Nucleolus :- Discovered by Fontana and Term by Bowman.
Nucleolus is naked or membraneless, rounded or slightly irregular structure present in nucleus and usually
attached to chromatin (or chromosomes) of specific site called Nucleolar organiser region/NOR.
Number of nucleolus in a nucleus is one. Onion cell has 4, and in oocytes of amphibian has 2000 nucleoli.
Nucleoli absent in sperm cell, muscle cell etc. Human cell has 5 nuleoli (13, 14, 15, 21 and 22nd).
Calcium is essential for maintenance of nucleolus. Nucleolus disappears during late Prophase and reappears
Chemistry of nucleolus :-
Electron microscope has shown nucleolus to be made of following parts :
(Ultrastructure of nucleolus) :
Fibrillar region :- This is central fibrous part of nucleolus, which is consist of mainly rDNA and proteins.
Granular region :- This is peripheral granular part of nucleolus which is consist of rRNA and proteins.
Amorphous matrix or pars amorpha :- This is proteinaceous ground matrix, which contains both fibrous
FUNCTIONS OF NUCLEOLUS
Ribosome formation is the chief role of nucleolus, thus is called as Ribosome factory of cell, the proteins of ribosome are synthesised in cytoplasm but it diffused in to nucleus and reach at nucleolus. Here rRNA and ribosomal proteins are assembled to form ribosomes which move to cytoplasm through nuclear pores.
KARYOSOME / CHROMCENTRE / FALSE NUCLEOLI
At some place hetrochromatin form thick, dark dense granule.
FUNCTIONS OF NUCLEUS
Genetic information :- Nucleus contains genetic information in its chromatin. (store house of genetic material) Transmission of genetic information :- Nucleus takes part in transmission of genetical information from parent cell to daughter cell or the one generation to next.
In cell-division :- Division of nucleus is pre-requisite to cell division.
Control of metabolism :- Nucleus controls metabolism of cell by sending m-RNA in cytosol (Basically biomolecule DNA controls cellular activities through directing synthesis of enzyme).
Variations :- Variation develope due to change in genetic material of nucleus. (Evolutionary role).
At the time of cell division the chromatin material get condensed to form chromosome, thus chromosome is highly condensed form of the chromatin. Chromosomes are not visible during interphase stage.
First of all, chromosomes was observed by Hofmeister (1818) and Karl Nageli in pollen mother cells (PMC) of Tradescantia.
Strasburger (1875) described chromosome structure appeared in nucleus during cell division. (Credit of discover of chromosomes goes to Strasburger)
Term “Chromosome” was proposed by Waldeyer in 1889. (Term ‘Chromatin, was suggested by Flemming.)
Trillium plant has longest chromosome.
Chromosomes can be best studies at metaphase stage because size of chromosome is the shortest during metaphase due to highly condensation of chromatin threads by gelation, dehydration and coiling.
(Shape of chromosome (V.L.J.I.) is studied at Metaphase stage)
Chromosomal theory of inheritance, was given by Sutton & Boveri.
Generally chromosomes in plants are larger than chromosomes of animals, but number of chromosome is high in animals as compared to plants.
Maximum no. of chromosome Aulocantha (protozoa) = 1600
Maximum no. of chromosome in plant ophioglossum (pteridophyta) = 1262
T.H. Tijo and Levon reported 2n = 46 in human cell.
2n = number of chromosome in diploid cell. n = number of chromosome in haploid cell.
x = Basic number in one set of earliest ancestor.
The number of chromosome is definate for each species. For example every normal human being has 46 chromosomes in each body cell.
Gametes of all diploid organisms contain only one of each chromsome. The number of chromosomes in a gamete is called “Genome” or haploid chromosome. (Human 23) “A complete set (n) of chromosome (all genes) inherited as a unit from one parent is known as genome”.
STRUCTURE OF CHROMOSOME
Pellicle :- This is outermost, thin proteinaceous covering or sheath of chromosome.
Matrix :- Ground substance of chromosome, which has different type of enzymes, minerals, water, proteins.Chromonema (singular chromonemata) :- Term by Vejdovsky. This is an important, gentical, highly coiled thread, throughout the length of a chromosome or chromatid . It was called chromonema.
Each chromonemata is consist of a single long thread of DNA associated with histone.
Sometimes bead like structure are seen on chromonema fibres, which are called as chromomeres
Type of coiling in chromonema -
Plectonemic-coiling :- When both the chromonema are inter twined and can not be separated easily. (in mitotic prophase chromosomes)
Paranemic coiling :- When both chromonema can be easily seperable. In meiotic prophase)
Centromere/Kinetochore :- (Primary constriction)
Each chromosome (at metaphase) is consist of two half chromosome or two chromatids. Both the chromatids of a chromosome are joined or connected by a structure called Centromere. At this point or centromere two protein discs are present which is called Kinetochore.
Kinetochores contitute the actual site of attachement of spindles to chromosomes during cells division.
Centromeric DNA is called as alphoid DNA (Hetrochromatic).
At the region of centromere the chromosome is comparatively narrower than remaining part of chromosome,thus it is termed as Primary constriction.
Chromatid :- At metaphase stage each chromosome is consist of two cylindrical structures - called Chromatids.Both sister chromatids or longitudinal half chromatids (in Anaphase or Telophase) or two chromatid. (as in metaphase)
Secondary constriction : Besides primary constrictions one or two, other constriciton may also occurs on some chromosome, which are known as secondary constriction. Secondary constriction is also known as NOR (Nucleolar organiser region) (13,14,15,21,22 chromosomes in human) Satellite / Trabent
Found in chromosome in which secondary constriction is found.
It is small spherical part of chromosome distal to secondary constriction.
Chromosome with satellite is called SAT chromosomes.
Tip of chromosome is known as telomere. (rich in guanine base) show polarity.
Perform two important function
It prevent ends of two chromosomes from sticking with each other. (fusing of chromosome)
Help chromosome in attachment to nuclear envelope.
Enzyme telomerase present in Telomere which is a type of Ribozyme.
Type of Chromosome on basis of position of centromere
Metacentric - Centromere in mid two arms are equal so chromosome is v-shaped.
Submetacentric - Centromere slightly away from mid so chromosome is L-shaped.
Acrocentric - Centromere occupies sub terminal position, so one arm is very long whereas other arm is extremely short. Acrocentric chromosome is J-shaped. [Arm ratio maximum]
Telocentric - Centromere occupies terminal most position so chromosome is single armed.
ULTRA STRUCTURE OF THE CHROMOSOME
Single strand models :- (Supported by crossing over)
Uninemal model :- Given by Ris. According to this model each chromatid of chromosome is consist of one DNA molecule.
Folded fibre model :- Proposed by Du Praw. According to this model, chromosome is consist of highly
folded single DNA molecule.
Nucleosome model :- Bead like structure in chromatin was first observed by Olin’s et al. This model was
proposed by Kornberg & Thomas in 1974.
It is most important and universally accepted model for the structure of chromosome. This model explain that how giant DNA molecule and histone (Chromatin) packeaged in to a chromosome.
Term nucleosome was given by P.Oudet in 1975.
“Nucleosome is a unit of chromatin (Chromosome) which is composed of about 200 base pairs of the
DNA and an Octamer (Core particle) of four types (H2A, H2B, H3 & H4) of histone proteins”. Nucleosome is also known as Nu-body or -particle / PS-particle.
Nucleosome = Binding DNA (146 bp) + Octamer + Linker DNA + H1 Histone
[Structural unit of Chromosome] [H2A, H2B, H3, H4 × 2]
6 Nucleosome unit super coilied to form Solenoid structure. (30 nm fibre) (by Klug - 1982)
H1 histone protein (sealing histone) joined the turns of binding DNA nucleosome.
SPECIAL TYPE OF CHROMOSOME (GIANT CHROMOSOME)
Lampbrush chromosome was first observed by Flemming (1882) in amphibian oocyte at Diplotene
stage of cell division.
A detail study was made by J. Ruckert (1892) in the oocyte of sharks.
Found in the oocytes of insect, sharks, amphibian, reptiles and birds which produce yolky eggs.
Lampbrush chromosome composed of main axis which possess series of chromomere.
Main axis formed of DNA and Protein.
Main axis give rise to lateral loops (composed of DNA). Lateral loops axis remain surrounded by matrix. Matrix is composed of RNA and Protein.
It is concerned with protein synthesis, yolk formation (vitellogenesis) and RNA synthesis.
POLYTENE CHROMOSOME / SALIVARY GLAND CHROMOSOME
It was discovered by Balbiani in 1881.
It is found in salivary gland of chironomous larva, Salivary gland, malphigian tubule, epithelial lining of drosophila, salivary glands of certain Diptera.
The larger size of chromosome is due to the presence of numerous chromatids. so called polytene(Many stranded) chromosome.
Numerous chromatids (512 to 1000) presence is because of repeted division of chromosome without centromeric and nuclear division such division is called endomitosis or endoreduplication [repeated replication of DNA].
Possess two types of transverse bands, dark band, which is Feulgen positive and posses more DNA,Light band is Feulgen negative which posses more RNA,Balbiani ring / puffs The bands get enlarged at certain place and because of uncoiling of chromonemata and form swelling called puffs or Balbiani ring.
Balbiani rings are concerned with synthesis of mRNA and protein.
Ecdyson hormone of insect stimulates formation of balbiani ring.
Polytene chromosome is related with metamorphosis of an insect.
SUPERNUMERARY / B-CHROMOSOME / ACCESSORY CHROMOSOME
In certain plants and animal one or more additional chromosome were observed in addition to the normal number called supranumerary chromosome (named by D.Jones).
It is genetically inert, Heterochromatic and small sized.
It is present in the nucleus.
Its presence does not effect an organism phenotypically if its number is high they reduce the fertility and vigour.
Wilson in 1905 discovered it in metapodium insect.
Increase ecological adaptation to organism.
It was seen in hybrid tobacco plant. Its size is 15 times more in comparison to normal chromosome.
Isochromosomes :- When the both arms of the chromosome are identical or gentically similar. Then chromosomes called as
isochromosomes. If arm of a telocentric chromosome is splitted upto centromere then a metacentric chromosome with two identical arms is formed. such chromosome is called isochromosome.
Ring chromsome : Prokaryotic chromosome are ring chromosome or consists of circular folded DNA
Sex chromosome :- May be XX or XY
Artificial chromosome :- HACs, MACs, YACs, BACs, etc.
Human Chromosomes :-
Human chromosomes are morphologically numbered into 7 groups (size and position of centromere)
A : 1 - 3 chromosome, largest size, submeta or metacentric.
B : 4 - 5 chromosome, less large size, submetacentric.
C : 6 - 12 chromosome, medium size, submetacentric.
D : 13 - 15 chromosome, shorter than group ‘c’, acrocentric and SAT chromosome.
E : 16 - 18 chromosome, short size, meta / submetacentric.
F : 19 - 20 chromosome, short size, metacentric.
G : 21 - 22 chromosome, smallest, Acrocentric & SAT.
X-chromosome - C-group, large size, submetacentric.
Y-chromosome - G-group, short size, acrocentric, satellite absent.
Karyotype :- Karyotype is external morphology of Chromosomes which is specific for each species of living organisms. Karyotype can be studied in metaphase of mitosis.
Karyotype includes the number of chromosomes, relative size, position of centromere, length of the arms,
secondary constrictions and banding patterns.
Banding technique is used to study of the specific pattern of band and interbands on chromosome. This include the use of flurochromes (Flurescent dyes).
Q-banding : It is obtained when chromosomes are stained with quinacrine mustard. It stains A-T rich areas (developed by casperson for Y chromosomes).
C-banding : It is used to stain constitutive heterochromatin, usually in centromeric region of the chromosome.
G-banding : Chromosomes are stained with Giemsa. It stains sulphur rich protein parts.
A variety of different bands are obtained by the modification of Q-banding and G-banding like C, T and
N-bands. Q, C, G and R banding used for animal karyotypes while C and N banding used in plants.
R-banding : The process involved incubation of the chromosomes in a buffer at high temperature followed by use of Giemsa stain. This brings about the visualization of sulphur deficient region of chromosomes thus named as reverse giemsa.