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In fluid mosaic model of plasma membrane
Fluid mosaic model of plasma membrane proposes that plasma membrane comprises of a phospholipid bilayer wherein icebergs of proteins floating in sea of phospholipids.
Which of the following occurs more than one and less than five in a chromosome?
A chromatid is one of two identical halves of a chromosome. Sister chromatids are 2 identical halves which are joined by the centromere in a chromosome. A chromomere is serially arranged beads of a chromosome that have resulted from the supercoiling of a continuous DNA thread. It is more distinct during prophase. Telomere is a cap-like structure present at the end of each strand of DNA. It protects the chromosome from sticking to another chromosome. It also protects the genetic material during cell division. It occurs 4 times in a chromosome.
Thus, the correct answer is 'Telomere.'
Ribosomes are produced in
Golgi bodies take part in elaboration and secretion of complex biochemicals. Mitochondria are the site of ATP synthesis. Ribosomes are produced in nucleolus.
Mitotic spindle is mainly composed of which protein?
Mitotic spindles are composed of microtubules which are made of tubulin dimers. Actin and myosin are the contractile proteins of muscle fibres. Myoglobin is oxygen carrying pigment found in muscle.
In which one of the following is nitrogen not a constituent ?
Raphides are needle-shaped crystals of calcium carbonate or calcium oxalate found in specialized plant cells called idioblasts. It is believed that the raphides are a defense mechanism against plant predators, as they are likely to tear the soft tissues of the throat or esophagus of a plant predator chewing on the plant’s leaves. They are non-nitrogenous substances.
Flagella of prokaryotic and eukaryotic cells differ in
Prokaryotes have simple flagella without microtubules whereas eukaryotes have complex cilia and flagella which consists of microtubules arranged in 9+2 fashion (an outer ring of nine pairs surrounding 1 center pair). Further in prokaryotes the arrangement is 9+0.
In chloroplasts, chlorophyll is present in the
The thylakoid membranes possess the chlorophylls. The outer membrane is permeable to a number of solutes. Inner membrane has a number of carrier proteins. Stroma forms the matrix containing the enzyme for Calvin cycle.
The main organelle involved in modification and routing of newly synthesized proteins to their destinations is
Endoplasmic reticulum transport proteins and enzymes to their destinations i.e. within the cell and outside the cell.
According to widely accepted “fluid mosaic model” cell membranes are semi-fluid, where lipids and integral proteins can diffuse randomly. In recent years, this model has been modified in several respects. In this regard, which of the following statements is incorrect?
Flip-Flop movement is due to migration of lipid molecules from one lipid monolayer to other monolayer of lipid bilayer.
A student wishes to study the cell structure under a light microscope having 10X eyepice and 45X objective. He should illuminate the object by which one of the following colours of light so as to get the best possible resolution?
Correct Answer :- a
Explanation : Resolution power is the ability of the lens to make the contents of a specimen very clear to observe.
To get good resolution the illumination light should have the shortest wavelength for clear vision.
Blue light has good wave lent to study a cell.
Centromere is required for:
During anaphase APC (anaphase promoting complex) develops. It degenerates proteins binding the two chromatids in the region of centromere.
As a result the centromere of each chromosome divides. This converts the two chromatids into daughter chromosomes.
Protein synthesis in an animal cell occurs
Protein synthesis in an animal cell occurs on ribosomes present in cytoplasm as well as in mitcohondria because mitochondria and chloroplast also have their own DNA, RNA and ribosome so can synthesize half of their required proteins.
Which of the following statement regarding mitochondrial membrane is not correct ?
The enzymes of electron transport system are present in inner mitochondrial membrane.
A major break through in the studies of cells came with the development of electron microscope. This is because
A major break through in cell studies came with the development of EM having great resolution power due to which we can see the ultrastructures of cell organelles.
Select the wrong statement from the following
Both chloroplasts and mitochoridria have an internal compartment, the thylakoid space bounded by double membrane
Which one of the following is not a constituent of cell membrane?
The biological membranes are made up of lipids and proteins. The various lipids present in the membrane are phospholipids, cerebrosides, gangliosides, cholesterol, glycolipids etc. Proline is an amino acid which is generally known as chain breaker because of its structure. Proline is generally absent in membrane proteins. Proline usually occurs in regions where protein chain makes sharp turns.
So, the correct answer is 'Proline'
Keeping in view the fluid mosaic model for the structure of cell membrane, which one of the following statements is correct with respect to the movement of lipids and proteins from one lipid monolayer to the other (described as flipflop movement)?
Keeping in view the ‘Fluid mosaic model” for the structure of cell membrane, the movement of lipids and proteins from one lipid monolayer to the other, lipid can rarely flip-flop, protein can not. The fluid mosaic model is the most important and widely accepted latest model for plasma membrane was given by Singer and Nicolson in 1972. According the them it is “ protein iceberg in a sea of lipids”.
Polysome is formed by
Polysome (Polyribosome) is a complex formed by several ribosomes attached to a single mRNA molecule in the process of translation.
Cellulose is the major component of cell walls of
Cellulose is a major component of cell wall of Pythium. Pythium is a genus of parasitic Oomycete. Because this group of organisms were once classified as fungi, they are sometimes still treated as such. Pythium, like others in the family Pythiaceae, are usually characterized by their production of coenocytic hyphae, hyphae without separations. Oogonia generally contain a single Oospore. Antheridia contain an elongated and club shaped antheridium.
The two sub-units of ribosome remain united a critical ion level of
The two subunits of ribosome remain united at a critical ion level of magnesium. The presence of magnesium and its amount plays an important role in the appearance and structure of the ribosomes. If magnesium is absent in medium, the large particles fall apart to present a group of smaller particles.
Vacuole in a plant cell
Vacuole in a plant cell is membrane bound and contains water and excretory substance. Vacuole is a space within the cytoplasm of living cell that is filled with air, water or other liquid, cell sap or food particles. In plant cells, there is usually one large vacuole bounded by a single layered membrane (tonoplast or vacuole membrane); animal cells usually have several small vacuoles.
Plasmodesmata are connections between adjacent cells. Plasmodesmata are narrow channels that act as intercellular cytoplasmic bridges to facilitate communication and transport of materials between plant cells. Plasmodesmata are formed during cell division, when traces of the endoplasmic reticulum become caught in the new wall that divides the parent cell.
Cytoskeleton is made up of:
The cytoskeleton is made up of three kinds of protein filaments actin filaments (also called microfilaments), intermediate filaments and microtubules whose major constituents are actin and tubulin respectively.
Stroma in the chloroplasts of higher plant contains:
Stroma in the chloroplasts of higher plant contains light independent reactions enzymes. Within the stroma are stacks of thylakoids, the sub-organelles which are the site of photosynthesis.
Middle lamella is composed mainly of:
Middle lamella is mainly composed of calcium pectate. Calcium is deposited in plants cell walls during their formation - it is required for the stability and function of cell membranes and acts as a type of ‘cementing agent’ in the cell walls in the form of calcium pectate’. Calcium pectate is like a glue binding adjacent cells together so if inadequate calcium is not transported during cell formation, tissues become less stable and prone to disintegration.