NCERT Solutions: Biomolecules

Q1: What are macromolecules? Give examples.
Ans: Macromolecules are very large biological molecules formed by the polymerisation of many small monomer units. They have high molecular weight and are often insoluble in water, so they may occur in a colloidal state in intercellular fluids. Common examples of macromolecules are proteins (polymers of amino acids), nucleic acids (polymers of nucleotides) and polysaccharides (polymers of monosaccharides such as starch and cellulose).

Q2: What is meant by the tertiary structure of proteins?
Ans: The tertiary structure of a protein is its overall three-dimensional folded shape formed when secondary structural elements (such as helices and sheets) fold and pack together. This folding arranges side chains so that many of the polar or charged groups are on the surface and the non-polar (hydrophobic) groups are buried inside. The tertiary structure is stabilised by several interactions, including hydrogen bonds, ionic bonds, hydrophobic interactions and disulfide bridges between cysteine residues. This precise three-dimensional shape is essential for the protein's biological activity because it positions the active and binding sites in the correct geometry.

Q3: Find and write down structures of 10 interesting small molecular-weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.
Ans:
(a)  

(b)

Q4: Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics etc.)
Ans:  Examples of proteins used as therapeutic agents include insulin (used to treat diabetes), antibodies and monoclonal antibodies (used in passive immunotherapy and targeted treatments), oxytocin (used to induce labour), antidiuretic hormone (ADH; used in certain kidney disorders), thrombin and fibrinogen (used in wound treatment and surgical applications), renin (in diagnostic and research use), and streptokinase (used as a clot-dissolving agent).
Other applications of proteins include:

• Use as food additives and flavour enhancers; for example, some protein extracts are used to improve texture and nutrition.
• Use in the food industry as artificial sweeteners or flavouring agents - for example, thaumatin is a protein used as a low-calorie sweetener.
• Use as dietary supplements to provide essential amino acids and to support growth and repair.
• Use in cosmetics and personal care products - proteins and protein derivatives (for instance, casein) are used in creams and shampoos to improve texture and conditioning properties.
• Industrial and biotechnological applications - enzymes (which are proteins) are widely used in detergents, leather processing, textile manufacture and biotechnology.

Q5: Explain the composition of triglyceride.
Ans: A triglyceride is formed when one molecule of glycerol is esterified with three fatty acid molecules, one on each of the glycerol's hydroxyl (-OH) groups. The bonds formed are ester linkages. Structurally, glycerol provides the three-carbon backbone and the fatty acids (which may be identical or different) are attached as long hydrocarbon chains with a terminal carboxyl group. When all three fatty acids are the same, the triglyceride is called a simple (or pure) fat; when they are different, it is called a mixed fat. The nature of the fatty acids (saturated or unsaturated) determines the physical properties of the triglyceride, such as melting point and solidity at room temperature.

All three fatty acids of a triglyceride in a pure fat are similar, while in mixed fat they are dissimilar.

Q6: Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).
Ans: Yes. Ball-and-stick model kits are suitable for building three-dimensional models of many biomolecules. In such kits, atoms are represented by coloured balls and bonds by connecting rods or sticks. These models help to visualise the geometry, bond angles and spatial arrangement of atoms in molecules such as amino acids, sugars (for example, D-glucose), small peptides and simple nucleotides. Colour conventions (for example, carbon grey, oxygen red/pink, hydrogen white/green, nitrogen blue) vary by manufacturer but are useful for quick identification. Models are valuable teaching aids for understanding molecular shape and stereochemistry.

Q7: Draw the structure of the amino acid, alanine.
Ans: The structure of alanine is shown below:

In words, alanine has an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom and a methyl group (-CH₃) attached to the central (α) carbon. Its molecular formula is C₃H₇NO₂. Alanine is a small, non-polar, neutral amino acid and the -CH₃ side chain makes it hydrophobic compared with amino acids having polar side chains.

Q8: What are gums made of? Is Fevicol different?
Ans: Gums are complex carbohydrates, generally classified as heteropolysaccharides, because they are built from more than one type of monosaccharide unit linked by glycosidic bonds. Natural gums (for example, gum arabic) are produced by plants and are used as emulsifiers, stabilisers and thickeners in the food and pharmaceutical industries. Fevicol, by contrast, is a synthetic adhesive; it consists of man-made polymers (for example, polyvinyl acetate-based formulations) and is not derived from natural polysaccharide gums. Thus, gums are natural carbohydrate polymers, whereas Fevicol is an artificial polymeric glue used for bonding materials.

Q9: Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.
Ans: Qualitative tests for proteins, amino acids and fats:

• Biuret test (for protein): When an alkaline solution of copper sulphate is added to a protein solution, a violet or purple colour develops if peptide bonds are present. This indicates proteins or polypeptides.
• Grease spot (or brown-paper) test for fats: Oils and fats leave a translucent or grease stain on brown paper that does not dry quickly. This shows the presence of lipids.
• Ninhydrin test (for free amino acids): Ninhydrin reagent reacts with free amino acids to give a blue, purple or pink colour; proline and hydroxyproline give a yellow colour.

When testing common samples, typical observations are:

• Fruit juice: Usually shows reducing sugars (test with Benedict's solution) and organic acids; proteins are generally absent or present in very small amounts; fats are absent.
• Saliva: May give a weak positive Biuret test (contains small amounts of proteins and enzymes such as amylase); it is not expected to contain fats.
• Sweat: Mainly water with salts and small organic compounds; it normally tests negative for proteins and fats.
• Urine: Normally negative for proteins and fats; the presence of protein (proteinuria) or fat indicates an abnormal condition and should be investigated clinically.

Q10: Find out how much cellulose is made by all the plants in the biosphere and compare it with how much of paper is manufactured by man and hence what is the consumption of plant material by man annually. What a loss of vegetation!
Ans: The biosphere produces an enormous amount of cellulose each year - estimates suggest roughly 100 billion tonnes of cellulose formed from about 170 billion tonnes of total organic matter. In comparison, industrial paper production uses a much smaller quantity of wood: about 0.5 billion tonnes of wood are used annually for making paper. Human use of plant material for food, timber, fuel, medicines and other products is substantial; for example, annual food requirements are estimated at around 1.5 billion tonnes and additional wood demand for various uses may be close to 2 billion tonnes. Although the human share is smaller than the total annual production of cellulose by plants, the concentrated and localised removal of vegetation for these uses causes significant loss of vegetation and impacts ecosystems.

Q11: Describe the important properties of enzymes.
Ans: The important properties of enzymes are as follows:

• Protein nature: Most enzymes are large globular proteins. Some enzymes require non-protein helpers (cofactors or coenzymes) to be active.
• Catalytic action: Enzymes accelerate chemical reactions without being consumed; they lower the activation energy required for the reaction.
• Specificity: Each enzyme is specific to its substrate or to a particular type of reaction - this specificity arises from the enzyme's unique active-site geometry.
• Reversibility: Many enzyme-catalysed reactions are reversible, and enzymes can catalyse both the forward and reverse reactions depending on conditions.
• Optimum conditions: Enzymes have optimum temperature and pH ranges at which their activity is maximal; deviations from these optima reduce activity.
• Inactivation: Enzymes can be inactivated by high temperature (denaturation), extreme pH, heavy metals, certain poisons and radiation.