Class 11 Biology - Biomolecules

Notes

Key Concepts

Analysis of Chemical Composition

• Organic Compounds: Living tissue (vegetable or liver) is ground in trichloroacetic acid (Cl₃CCOOH). Filtering through cheesecloth yields two fractions:
  • Acid-soluble pool (Filtrate): Contains thousands of small organic compounds (micromolecules).
  • Acid-insoluble fraction (Retentate): Contains macromolecules like proteins, polysaccharides, and nucleic acids.
• Inorganic Elements: Obtained by burning tissue to "ash." Elements like Calcium, Magnesium, Sodium, and compounds like sulphate and phosphate are identified.
• Biomolecules: All carbon compounds obtained from living tissues.

Amino Acids

• Structure: Organic compounds containing an amino group (-NH₂) and an acidic carboxyl group (-COOH) on the same α-carbon. They are substituted methanes.
• R Group: The variable group determines the amino acid.
  • Glycine (R = H)
  • Alanine (R = -CH₃)
  • Serine (R = -CH₂OH)
• Types: 20 types occur in proteins. Can be acidic (Glutamic acid), basic (Lysine), neutral (Valine), or aromatic (Tyrosine, Phenylalanine, Tryptophan).
• Zwitterion: In different pH solutions, the structure changes due to the ionizable nature of amino and carboxyl groups.

Lipids

• Generally water-insoluble.
• Fatty Acids: Carboxyl group attached to an R group (1-19 carbons). Palmitic acid (16C), Arachidonic acid (20C). Can be saturated (no double bonds) or unsaturated.
• Glycerol: Trihydroxy propane.
• Triglycerides: Glycerol esterified with three fatty acids.
• Phospholipids: Lipids with a phosphorus and a phosphorylated organic compound (e.g., Lecithin in cell membranes).

Nitrogen Bases, Nucleosides, and Nucleotides

• Nitrogen Bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Uracil, Thymine).
• Nucleosides: Nitrogen base + Sugar (e.g., Adenosine, Guanosine, Uridine, Cytidine).
• Nucleotides: Nucleoside + Phosphate group (e.g., Adenylic acid, Guanylic acid). These are the building blocks of nucleic acids (DNA and RNA).

Primary and Secondary Metabolites

• Primary Metabolites: Have identifiable functions and roles in normal physiological processes (e.g., amino acids, sugars).
• Secondary Metabolites: Produced in plants, fungi, and microbes; functions are not always clear but useful to human welfare (e.g., alkaloids, rubber, antibiotics, spices, pigments).

Biomacromolecules

• Found in the acid-insoluble fraction with molecular weights > 10,000 Da (except lipids).
• Proteins: Heteropolymers of amino acids. Linear chains linked by peptide bonds.
  • Collagen: Most abundant protein in the animal world.
  • RuBisCO: Most abundant protein in the whole biosphere.
• Polysaccharides: Long chains of sugars.
  • Cellulose: Homopolymer of glucose; found in plant cell walls.
  • Starch: Energy store in plants; forms helical secondary structures.
  • Glycogen: Energy store in animals.
  • Chitin: Complex polysaccharide in arthropod exoskeletons.
• Nucleic Acids: Polynucleotides (DNA/RNA).

Structure of Proteins

1. Primary Structure: The sequence/positional information of amino acids.
2. Secondary Structure: Folding of the thread into forms like the α-helix (right-handed) or β-pleated sheets.
3. Tertiary Structure: 3D folding of the protein chain upon itself; essential for biological activity.
4. Quaternary Structure: Assembly of multiple polypeptide subunits (e.g., Haemoglobin: 2α and 2β subunits).

Enzymes

• Nature: Almost all are proteins. Some are nucleic acids (Ribozymes).
• Mechanism: Have an 'active site' (crevice) where the substrate fits. They lower the Activation Energy required for a reaction.
• Catalytic Cycle:
  1. Substrate binds to active site.
  2. Enzyme alters shape (induced fit).
  3. Bonds broken/made; ES complex forms transition state.
  4. Products released; enzyme ready for next cycle.
• Factors Affecting Activity:
  • Temperature & pH: Each has an optimum. High temp denatures proteins.
  • Substrate Concentration: Rate increases until Vmax is reached (enzyme saturation).
  • Inhibitors: Chemicals that shut off activity. Competitive inhibitors resemble the substrate (e.g., Malonate inhibits Succinic dehydrogenase).
• Classification:
  1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases.
• Co-factors: Non-protein constituents making the enzyme active.
  • Apoenzyme: Protein portion.
  • Prosthetic groups: Tightly bound (e.g., Haem).
  • Co-enzymes: Transiently bound organic compounds (e.g., NAD, NADP containing Niacin).
  • Metal Ions: e.g., Zinc for carboxypeptidase.