Class 11 Biology - Biomolecules

Exercises

1. What are macromolecules? Give examples.

Answer: Macromolecules (or biomacromolecules) are large, complex chemical compounds found in the acid-insoluble fraction of living tissues. They have molecular weights ranging from 10,000 daltons and above. With the exception of lipids, all macromolecules are polymeric substances.

Examples:

• Proteins: Polymers of amino acids.
• Polysaccharides: Polymers of monosaccharides (e.g., starch, cellulose).
• Nucleic Acids: Polymers of nucleotides (DNA and RNA).

2. What is meant by tertiary structure of proteins?

Answer: The tertiary structure of a protein refers to the three-dimensional view of the protein formed when the long protein chain (polypeptide) is folded upon itself like a hollow woolen ball. It involves interactions between the R-groups of the amino acids. Significance: This 3D conformation is absolutely necessary for the many biological activities of proteins, such as forming the active sites of enzymes.

5. Explain the composition of triglyceride.

Answer: A triglyceride is a simple lipid formed from one molecule of glycerol (trihydroxy propane) and three molecules of fatty acids. Each of the three hydroxyl (-OH) groups of the glycerol molecule is esterified with the carboxyl (-COOH) group of a fatty acid. These fatty acids can be saturated or unsaturated.

7. Draw the structure of the amino acid, alanine.

Answer: Alanine is an $\alpha$-amino acid where the R-group is a methyl group ($-CH_3$). The structure is:

      NH2
       |
  H —  C — COOH
       |
      CH3

11. Describe the important properties of enzymes.

Answer:

1. Chemical Nature: Almost all enzymes are proteins (exceptions include ribozymes which are RNA).
2. Efficiency: They are highly efficient biocatalysts, increasing reaction rates by millions of times (e.g., carbonic anhydrase).
3. Specificity: Each enzyme is highly specific for a particular substrate and reaction.
4. Active Site: They possess a specific pocket or crevice called the 'active site' where the substrate binds.
5. Lowering Activation Energy: They function by lowering the activation energy barrier required for a chemical reaction to proceed.
6. Sensitivity to Temperature and pH: They function optimally in narrow ranges of temperature and pH; extreme heat denatures them.
7. Saturation: At high substrate concentrations, the reaction reaches a maximum velocity (V_max) because all enzyme active sites are occupied.
8. Reversibility: Most enzymatic reactions are reversible.
9. Co-factors: Some enzymes require non-protein co-factors (prosthetic groups, co-enzymes, or metal ions) to become catalytically active.