Class 11-science NCERT Solutions Biology Chapter 9 - Biomolecules

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161

Biomolecules Exercise 160

Solution 1

The biomolecules formed by the polymerisation of a large number of micromolecules with higher molecular weight are known as macromolecules. These occur in colloidal state in intracellular fluid as they are insoluble in nature. Examples: Proteins and polysaccharides

Solution 2

i. Glycosidic bond: A glycosidic bond is a bond which joins a carbohydrate (sugar) molecule to another group, not essentially a carbohydrate. It is formed during dehydrate synthesis of a polysaccharide with one monosaccharide providing the hydroxyl group (-OH) and the other providing the hydrogen (-H) to form a molecule of water (H₂O).

ii. Peptide bond: A peptide bond (amide bond) is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water (H₂O). This is a dehydration synthesis reaction (also known as a condensation reaction) and usually occurs between amino acids. The resulting CO-NH bond is called a peptide bond, and the resulting molecule is an amide. Polyamides such as nylons and aramids are synthetic molecules (polymers) which possess peptide bonds.

iii. Phosphodiester bond: A phosphodiester bond is a group of strong covalent bonds between a phosphate group and two other molecules to form two ester bonds. Phosphodiester bonds make up the backbone of the strands of DNA. In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon of another sugar molecule.

Solution 3

The tertiary structure is a structure formed by the folding of secondary coiled polypeptides forming a hollow, woollen ball-like structure. It is folded in such a way that the functional side groups are present on the surface and the inactive side groups remain in the interior.

Solution 4

(a)

Molecule	Structure
i. Uridine
ii. Cholesterol
iii. Ribose
iv. Uracil
v. Glycerol
vi. Adenosine
vii. Glucose
viii. Glycine
ix. Phospholipid
x. Adenylic acid

(b)

	Compound	Manufacturer	Buyer
i.	Starch products	Kosha Impex (P) Ltd.	Research laboratories, educational institutes and other industries which use biomolecules as a precursor for making other products.
ii.	Liquid glucose	Marudhar apparels
iii.	Various enzymes such as amylase, protease and cellulase	Map (India) Ltd.

Solution 5

In the primary structure of a protein, amino acids show linear arrangement. To sequence an entire polypeptide chain, a chemical method called Edman degradation was devised by Pehr Edman. This procedure labels and removes only the amino terminal residue from a polypeptide, leaving all other peptide bonds intact. So, the amino acids are labelled, removed and identified one by one. By this method, we can connect the information to determine the homogeneity of a protein.

Solution 6

List of proteins used as therapeutic agents: Insulin, Oxytocin, Antidiuretic Hormone (ADH), Thrombin, Fibrinogen, Renin, Immunoglobulin, Diastase and Streptokinase.

Other applications:

i. Cosmetics: Proteins are used in beauty creams and shampoos. Example: Casein

ii. Sweeteners: Some proteins are used as sweeteners. Example: Thaumatin is a low-calorie sweetener and flavour modifier.

iii. Dietary proteins: Proteins are added to dietary supplements for body building and maintenance of health.

Solution 7

Triglycerides are formed from a single molecule of glycerol combined with three fatty acids on each of the OH groups through ester bonds.

In pure fat, all the three fatty acids of a triglyceride are similar (e.g. tripalmitin), while in mixed fat, they are dissimilar (e.g. palmito-oleo-stearin).

Biomolecules Exercise 161

Solution 8

During the bacterial fermentation of milk proteins, the bonds which maintain their secondary and tertiary structures are broken. So, milk proteins, such as casein, undergo denaturation, and the globular proteins transform into fibrous proteins having only the primary structure. This changes milk into curd or yoghurt.

Solution 9

Yes. The biomolecules can be represented by the ball and stick model. The bonds which hold the atoms are represented by sticks, whereas the atoms are represented by balls.

Example: In the model of D-glucose, the oxygen atoms are represented by pink balls, the hydrogen atoms by green balls, while the carbon atoms are represented by grey balls.

Solution 10

The pH of amino acid is recorded. The weak base is slowly added to it, and the pH is recorded continuously. The number of inflexions indicates the number of ionisable functional groups -COOH in the acidic range and -NH₂ in the alkaline range.

Solution 11

Solution 12

Gums are natural heteropolysaccharides and are formed of a large number of different monosaccharide units linked together by glycosidic bonds. Fevicol is different from gums as it comprises synthetic polymers.

Solution 13

Qualitative tests for proteins, amino acids and fats:

i. Biuret test: The Biuret test for protein identifies the presence of protein by producing light blue to purple colour of the solution.

ii. Grease test for oil: Certain oils give a translucent stain on brown paper. This test can be used to show the presence of fat in vegetable oils.

iii. Ninhydrin test: If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue or purple colour depending on the type of amino acid.

Item		Name of the test	Procedure	Result	Inference
i.	Fruit juice	Biuret test	Fruit juice + Biuret's reagent	Colour changes from light blue to purple.	Presence of protein.
		Grease test	Add a few drops of fruit juice on brown paper.	No translucent drop formed.	Absence of fats and oils.
		Ninhydrin test	Fruit juice + Ninhydrin reagent + Boil for 5 min	Colourless solution changes to pink, blue or purple colour.	Presence of amino acids.
ii.	Saliva	Biuret test	Saliva + Biuret's reagent	Colour changes from light blue to purple.	Presence of protein.
		Grease test	Add a few drops of saliva on brown paper.	No translucent drop formed.	Absence of fats and oils.
		Ninhydrin test	Saliva + Ninhydrin reagent + Boil for 5 min	Colourless solution changes to pink, blue or purple colour.	Presence of amino acids.
iii.	Sweat	Biuret test	Sweat + Biuret's reagent	No colour change	Absence of proteins.
		Grease test	Add a few drops of sweat on brown paper.	Oily appearance	Fats/oils may be present.
		Ninhydrin test	Sweat + Ninhydrin reagent + Boil for 5 min	No colour change; solution remains colourless.	Absence of amino acids.
iv.	Urine	Biuret test	Urine + Biuret's reagent	Colour changes from light blue to purple.	Presence of protein.
		Grease test	Add a few drops of urine on brown paper.	Little bit of oily appearance.	Fats may or may not be present.
		Ninhydrin test	Urine + Ninhydrin reagent + Boil for 5 min	Colourless solution changes to pink, blue or purple colour.	Presence of amino acids.

Solution 14

About 100 billion tonne of cellulose is formed annually in the biosphere out of 170 billion tonne of total organic matter. Paper making consumes about 0.5 billion tonne of wood. Trees are also used to fulfil other requirements of human beings such as medicines, timber and food. A rough estimate shows that food grains constitute 1.5 billion tonne. Full wood required is 2 billion tonne. Hence, it is difficult to calculate the annual consumption of plant material by man. The increase in consumption of cellulose has resulted in a great loss of vegetation.

Solution 15

Properties of enzymes:

i. Chemical nature: Enzymes are generally complex macromolecules of globular proteins. They do not initiate a chemical reaction but increase the rate of chemical reaction.

ii. Molecular weight: Being proteinaceous in nature, the enzymes are giant molecules with a molecular weight of 6000 to 4,600,000.

iii. Changeless form: Enzymes are not transformed in the chemical reaction. They combine temporarily with the substrate molecules but are not consumed or changed permanently in the reaction they catalyse.

iv. Action specificity: The enzymes are specific in their action. They catalyse only a particular kind of reaction and may even react on a particular substrate. Example: Enzyme maltase acts on sugar maltose but not on lactose or sucrose.

v. Heat sensitivity: All enzymes are heat sensitive, i.e. they are thermolabile.

vi. pH sensitivity: Each enzyme functions at a particular pH. Example: Pepsin, a digestive enzyme in the stomach, works best at a pH 2. A change in the pH makes the enzyme ineffective.