NCERT Solutions for Class 11 Biology Chapter 9 Biomolecules

Short Note:

• Chemical Analysis: Living tissue ground in Trichloroacetic acid (CCl₃COOH) yields two fractions when filtered through cheesecloth:

  1. Acid-soluble Pool (Filtrate): Contains biomicromolecules with molecular weights ranging from 18 to 800 Daltons (e.g., amino acids, monosaccharides, nucleotides).

  2. Acid-insoluble Fraction (Retentate): Contains biomacromolecules with molecular weights above 10,000 Daltons (e.g., proteins, nucleic acids, polysaccharides).

• Lipids Special Case: Lipids have molecular weights under 800 Da, but form membrane vesicles during grinding that stay in the acid-insoluble fraction. Hence, lipids are macromolecular fractions though strictly not macromolecules.

• Primary Metabolites: Direct involvement in normal physiological functions and growth (e.g., glucose, amino acids, ribose).

• Secondary Metabolites: Produced by plants, fungi, and microbes with ecological importance (e.g., Alkaloids like Morphine, Pigments like Carotenoids, Toxins like Abrin/Ricin, Drugs like Vinblastine/Curcumin, Polymeric substances like Rubber/Gums).

Short Note:

• Amino Acids: Organic compounds containing an amino group (-NH₂) and an acidic carboxyl group (-COOH) attached to the same α-carbon (substituted methanes).

  - Vary based on 'R' group (Glycine - H, Alanine - CH₃, Serine - CH₂OH).

  - Existing as Zwitterions at specific pH levels with simultaneous positive and negative charges.

• Proteins: Heteropolymers of amino acids linked sequentially by peptide bonds (-CO-NH- formed via dehydration synthesis).

  - Collagen: Most abundant protein in the animal world.

  - RuBisCO: Most abundant protein in the entire biosphere.

Short Note:

• Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds.

  - Homopolysaccharides: Single monomer unit (e.g., Starch, Cellulose, Glycogen, Chitin).

  - Starch: Forms helical secondary structures holding iodine molecules, turning blue-black with I₂ (cellulose lacks helices and cannot hold I₂).

• Nucleic Acids: Polymers of nucleotides linked by phosphodiester bonds.

  - Nucleotide = Nitrogenous Base + Pentose Sugar + Phosphate group.

  - Bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine, Uracil).

• Levels of Protein Structure:

  1. Primary Structure: Positional sequence of amino acids (N-terminal first, C-terminal last).

  2. Secondary Structure: Helical folding (α-helix or β-pleated sheets) stabilized by hydrogen bonds.

  3. Tertiary Structure: 3D folding forming active sites; necessary for biological activity.

  4. Quaternary Structure: Spatial arrangement of multiple polypeptide subunits (e.g., Hemoglobin with 2α and 2β subunits).

Short Note:

• Biological catalysts (mostly proteins, except catalytic RNAs called Ribozymes) that lower the activation energy required for a chemical reaction.

• Active Site: Specific pocket or crevice on the tertiary structure where the substrate binds to form an Enzyme-Substrate (ES) complex.

• Factors Affecting Enzyme Activity:

  - Temperature & pH: Exhibit optimum curves; extreme high temperature denatures proteins.

  - Substrate Concentration: Velocity increases up to V_max. K_m (Michaelis-Menten constant) represents substrate concentration at half V_max.

• Inhibition: Competitive Inhibition occurs when inhibitor closely resembles the substrate (e.g., Malonate inhibiting Succinic Dehydrogenase).

• Cofactors: Non-protein constituents required for activity.

  - Prosthetic groups: Tightly bound organic factors (e.g., Haem in peroxidase/catalase).

  - Co-enzymes: Transiently bound organic factors (e.g., NAD, NADP containing Niacin).

  - Metal ions: Form coordination bonds (e.g., Zinc for Carboxypeptidase).