POLYMERS AND POLYMERIZATION:
Macromolecules, both natural and man-made, own their great size to the fact they are polymers (Greek: many parts); that is, each one is made up of a large number of simpler units - identical to each other or at least chemically similar - joined together in a regular way. They are formed by a process we touched on earlier: polymerization. The joining together of many small molecules to form very large molecules. The simple compounds from which polymers are made are called monomers.
Petides and Proteins:
In the last section, you studied the polymers of monosaccharides which act as structural components in plants and serve as energy storage in animals. In this section, you will study another kind of natural polymers called peptides and proteins.
Peptides are biologically important polymers in which 2-amino acids are joined by the amide linkages, formed by the reaction of the carboxy group of one amino acid with the amino group of another amino acid. These amide linkages are also called peptide bonds. The general structure of a peptide is shown below:
Peptides can be classified as dipeptides, tripeptides and tetrapeptides, depending on whether the number of amino acids are two, three or four, respectively. Peptides containing upto 50 amino acids are called polypeptides. Bradykinin is an important naturally occurring nonapeptide which is present in blood plasma and is involved in the regulation of blood pressure.
Arg—Pro — Pro — Gly — Phe — Ser — Pro — Phe — Arg
Configuration of proteins :
(a) Biological nature or function of protein was confirmed by its conformation.
(b) This conformation is of 4 types:
Primary Structure :
This type of structure was given by Friedrich Sanger in 1953 in Insulin (of one chain).
Secondary Structure :
Eg. Myosin, Keratin etc.
(ii) β-pleated sheet
Eg. Silk fibres.
Tertiary structure :
In this structure of protein, atoms are highly coiled and form a spherical form
This structure is formed by 4 regular hydrogen bonds which makes a regularity in it.
(i) Hydrogen bond :
= O …….. H -
They are formed between oxygen of acidic amino acid and H of basic amino acid.
(ii) Hydrophobic bond -
(iii) lonic bond :
These are salt bonds formed between oppositely charged groups in side chains of Amino acids.
Eg. Aspartic acid
(iv) Disulphide bonds :
| ——— S - S —— |
Quaternary structure :
Types of proteins:
Classification of protein is based upon three general properties shape, Solubility and Chemical composition.
It is formed of only Amino Acids.
(A) Fibrous :
Ex. Collagen, Keratin etc.
(B) Globular :
(Protein Nucleic acid), Phosphoproteins (Protein (PO3)2-).
Eg. Casein of milk., Vitelline of egg - yolk.
Derived proteins :
(a) These are obtained as a result of partial hydrolysis of natural proteins.
Eg. → Proteose, Metaproteins, Peptones
(b) Denaturation of Proteins
When a protein in its native form, is subjected to a physical change like change in temperature, or a chemical change like change in pH, the native conformation of the molecule is disrupted and proteins so formed are called denaturated proteins.
The denaturation may be reversible or irreversible. The coagulation of egg on boiling is an example of irreversible protein denaturation.
However, it has been shown now that in some cases, the process is actually reversible. The reverse process is called renaturation.
Test of Protein :
(a) With conc. HNO3 on heating give yellow ppt. which on more heating gives solution on adding NH4OH. Red colour appears. It is Xanthoprotic test.
(b) Dil. CuSO4 protein give Blue violet colour. It is a Biuret test.
(c) Millon reaction: Proteins on adding Millon's reagent (a solution of mercuric and mercurous nitrates in nitric acid containing a little nitrous acid) followed by heating the solution gives red precipitate or colour.
(d) Ninhydrin reaction. Proteins, peptides and α-amino acids give a characteristic blue colour on treatment with ninhydrin.
Biological Importance of protein :
(a) Component of plasma membrane.
(b) All enzymes are proteins.
(c) Many hormones are proteins.
(d) Antigen and antibodies are protein.
(e) Actin and myosin proteins are important in muscle contraction.
(f) Proteins are important in growth, regeneration and repairing.
(g) Calorific value- 4.0 kcal.
(a) 'Lipid' word is derived from Greek word lipos which means fat.
(b) Lipids are heterogeneous group of substances which have common property of being relatively insoluble in water and soluble in non-polar solvents such as ether, Chloroform etc.
(c) Form 3-5% part of protoplasm.
(d) H2O ≠ 2 : 1 (different from water)
(e) Ratio of oxygen is less.
(f) Specific gravity < 1
Simple lipid :
(a) These are esters of fatty acids with glycerol.
Ester bond is present.
(b) Synthesis is of following type-
(c) Fatty acids which occur in natural fats usually contain an even number of carbon atoms(4 to 30) in straight chains.
(d) Simplest fatty acid HCOOH.
(e) More complex fatty acid are formed by successive addition of -CH2 groups.
(i) Saturated :
⇒ Only single bond is present in them.
⇒ First member is CH3COOH.
Other examples :
⇒ Palmitic acid - C15H31COOH
→ CH3(CH2)14 COOH
⇒ Stearic acid - C17H35COOH
⇒ Palmitic and stearic acid is found in fats of animals in less amount.
⇒ These are solid and are found in fats.
(ii) Unsaturated :
⇒ Double bond is present in these fatty acid chains.
⇒ These are liquids at room temperature. Found in Oils.
⇒ These are of two types:
Monounsaturated - 1 Double bond is present.
Eg. Oleic acid.
⇒ Oleic acid is present in more amount in nature.
Polyunsaturated - More than two double bonds
Eg. Linoleic acid with two double bonds.
Linoleinic acid with three double bonds.
Arachidonic acid with four double bonds (Groundnut).
⇒ These are esters of other alcohols of high
molecular weight instead of glycerols.
⇒These are insoluble in water.
⇒ These are monohydric alcohols.
⇒ Some examples of waxes -
Myricye palmitate (Honeybee wax) Cetyl palmitate (Dolphin and whale wax)
Cerumen (ear wax)
Compound Lipid- Are of 4 types :
(a) Phospholipids. (b) Glycolipids.
Phosphorous is present.
ex. cell wall
⇒ Lipid Sugar = Glycolipids
⇒ Present in brain, Adrenal glands, kidney, WBC liver, thymus, Spleen, Lungs, egg yolk.
⇒ Glycolipids = 2 Fatty acid 1 sphinocine 1 galactose.
⇒ By hydrolysis of fats, they are obtained.
⇒ These are different from other fats.
⇒ It is insoluble in water.
(i) Bile acids :
⇒ Present in secretion of liver.
(ii) Sex hormones :
⇒ These are androsterones.
(iii) Adrenal hormone- Eg : Aldosterone
⇒ They have -OH groups.
⇒ They are complex monohydroxy alcohols.
(i) Cholesterol - It is widely distributed in all cells of body.
Biological importance of Fats :
⇒ It is source of energy.
⇒ It is important for absorption of vitamin A, D, E and K.
⇒ It is important component of plasma membrane.
⇒ It act as shock absorber of body.
⇒ Calorific value: 9.3 kcal.