Biomolecules

NCERT Class 11 Biology • Chapter 9 Solutions

Structure & Classification

1. What are macromolecules? Give examples.

Macromolecules (or biomacromolecules) are large biological molecules found in the acid-insoluble fraction of living tissue. They typically have molecular weights greater than 10,000 Daltons (except lipids, which are smaller but aggregate).

They are formed by the polymerization of smaller building blocks (monomers).

Examples:
1. Proteins: Polymers of amino acids.
2. Nucleic Acids: Polymers of nucleotides (DNA, RNA).
3. Polysaccharides: Polymers of monosaccharides (Starch, Cellulose).
*(Lipids are often grouped here due to their solubility properties but are strictly not polymers).*
2. What is meant by tertiary structure of proteins?
[Image of Protein Tertiary Structure]

The Tertiary Structure refers to the overall three-dimensional shape of a protein molecule. It involves the further folding and coiling of the secondary structure (alpha-helices and beta-sheets) into a compact, globular form.

This structure is stabilized by various bonds:

  • Hydrogen bonds
  • Disulphide bridges ($-S-S-$)
  • Ionic bonds (Electrostatic interactions)
  • Hydrophobic interactions
  • Van der Waals forces

Significance: The tertiary structure is absolutely necessary for the biological activity of proteins (e.g., enzymes, receptors).

Small Biomolecules & Applications

3. Find and write down structures of 10 interesting small molecular weight biomolecules.

Small Biomolecules (Micromolecules):

  1. Glucose ($C_6H_{12}O_6$): Primary energy source.
  2. Ribose ($C_5H_{10}O_5$): Sugar in RNA.
  3. Glycine ($NH_2-CH_2-COOH$): Simplest amino acid.
  4. Alanine ($CH_3-CH(NH_2)-COOH$): Amino acid.
  5. Adenosine: Nucleoside (Adenine + Ribose).
  6. ATP (Adenosine Triphosphate): Energy currency.
  7. Cholesterol ($C_{27}H_{46}O$): Lipid component.
  8. Urea ($NH_2-CO-NH_2$): Nitrogenous waste.
  9. Citric Acid: Krebs cycle intermediate.
  10. Adrenaline (Epinephrine): Hormone.
Industry & Buyers:
Most are manufactured by pharmaceutical and chemical industries (e.g., Merck, Sigma-Aldrich).
Buyers: Research institutes, Hospitals, Food industry, Fitness supplement companies.
4. Find out proteins used as therapeutic agents and other applications.
Protein Therapeutic Application
Insulin Treatment of Diabetes Mellitus.
Thrombin/Fibrinogen Blood clotting agents.
Erythropoietin Treatment of Anemia.
Streptokinase Dissolving blood clots (Heart attack treatment).
Immunoglobulins Boosting immunity.

Other Applications:
– Cosmetics: Collagen and Elastin (anti-aging creams), Keratin (shampoos).
– Food Industry: Casein (cheese), Gluten (baking), Gelatin (desserts).
– Detergents: Proteases and Lipases (stain removal).
5. Explain the composition of triglyceride.
[Image of Triglyceride Structure]

A Triglyceride (or neutral fat) is an ester derived from glycerol and three fatty acids.

  • Glycerol: A trihydroxy alcohol ($CH_2OH-CHOH-CH_2OH$).
  • Fatty Acids: Long hydrocarbon chains with a carboxyl group ($-COOH$). Example: Palmitic acid, Oleic acid.

Reaction: One molecule of glycerol combines with three molecules of fatty acids via ester bonds, releasing three molecules of water (dehydration synthesis).

Models & Structures

6. Building models of biomolecules (Ball and Stick).

Yes, it is possible. Ball and Stick models are excellent for visualizing the 3D structure of biomolecules.

  • Balls: Represent atoms (Carbon-Black, Hydrogen-White, Oxygen-Red, Nitrogen-Blue).
  • Sticks: Represent bonds between atoms.

You can build simple molecules like Glucose, Amino acids (Glycine, Alanine), or even small peptides to understand bond angles and spatial arrangement.

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

Alanine is an alpha-amino acid.

Structure:
$\quad \quad H$
$\quad \quad |$
$H_2N – C – COOH$
$\quad \quad |$
$\quad \quad CH_3 \quad (\text{R-group is Methyl})$
8. What are gums made of? Is Fevicol different?

Natural Gums: Are polysaccharides (heteropolysaccharides) formed from different monosaccharide units. They are produced by plants (e.g., Acacia) usually in response to injury. They are water-soluble/colloidal.

Fevicol: Is different. It is a synthetic adhesive composed of Polyvinyl Acetate (PVA) resin. It is not a natural biological gum but a synthetic polymer.

Analysis & Enzymes

9. Qualitative tests for biomolecules.
Component Test Observation
Protein Biuret Test Violet colour.
Fats/Oils Sudan III / Grease Spot Red droplets / Translucent spot on paper.
Starch Iodine Test Blue-Black colour.
Reducing Sugar Benedict’s Test Brick Red precipitate.

Applications: Fruit juice (Sugar+), Urine (Sugar+ in diabetics, Protein+ in kidney issues), Sweat/Saliva (Amylase in saliva breaks starch).

10. Cellulose production vs Paper consumption.

Cellulose Production: Plants produce an estimated 100 billion tonnes of cellulose annually in the biosphere. It is the most abundant organic polymer on Earth.

Paper Consumption: Man produces approx 400 million tonnes of paper annually. While this is a small fraction of total cellulose, paper production targets specific trees (softwoods), leading to significant deforestation and loss of biodiversity in specific ecosystems.

11. Describe the important properties of enzymes.
  1. Protein Nature: Almost all enzymes are proteins (except ribozymes).
  2. Catalytic Power: They speed up reactions by lowering the activation energy. They do not get consumed in the reaction.
  3. Specificity: Enzymes are highly specific. A specific enzyme catalyzes only a specific reaction (Lock and Key / Induced Fit model).
  4. Optimum Conditions: They work best at a specific Temperature and pH. Deviations can denature them.
  5. Reversibility: Many enzyme-catalyzed reactions are reversible.
  6. Sensitivity: They are sensitive to inhibitors and poisons.
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