Biomolecules Exercise Solutions | KalviGavani

Primary metabolites are biomolecules directly involved in growth, development, and reproduction. They are found in all organisms. - Examples: Amino acids, sugars, lipids, nucleic acids Secondary metabolites are compounds not directly involved in normal growth but have ecological roles like defence. They are found in specific groups. - Examples: Alkaloids (caffeine, quinine), flavonoids, terpenes, tannins, resins

| Feature | DNA | RNA | |---|---|---| | Sugar | Deoxyribose | Ribose | | Bases | A, T, G, C | A, U, G, C | | Structure | Double-stranded helix | Usually single-stranded | | Location | Nucleus, mitochondria, chloroplast | Nucleus and cytoplasm | | Function | Stores genetic information | Protein synthesis (mRNA, tRNA, rRNA) |

The induced-fit model was proposed by Daniel Koshland. It states that the enzyme's active site is not rigid — it is flexible. When the substrate approaches, the active site changes its shape slightly to accommodate the substrate and form the enzyme-substrate complex. This is more accurate than the lock-and-key model.

Co-factors are non-protein components required for enzyme activity. The protein part of the enzyme is called the apoenzyme. Types: 1. Co-enzymes: Organic molecules derived from vitamins (e.g., NAD, FAD, CoA). They are loosely bound. 2. Prosthetic groups: Tightly bound co-factors (e.g., haem in catalase). 3. Metal ions: Inorganic ions (e.g., Mg²⁺, Zn²⁺, Fe²⁺). Apoenzyme + Co-factor = Holoenzyme (active enzyme)

Carbohydrates are organic compounds with the general formula Cn(H₂O)n. They are classified based on the number of sugar units: 1. Monosaccharides (Single sugar units): - Cannot be hydrolysed further into simpler sugars - Classified by number of carbons: trioses (C₃), tetroses (C₄), pentoses (C₅), hexoses (C₆) - Examples: Glucose (blood sugar), Fructose (fruit sugar), Galactose, Ribose (in RNA), Deoxyribose (in DNA) - Glucose: C₆H₁₂O₆; most important energy source 2. Disaccharides (Two sugar units): - Formed by condensation of two monosaccharides (removal of water) - Linked by glycosidic bond - Examples: - Sucrose = Glucose + Fructose (cane sugar) - Maltose = Glucose + Glucose (malt sugar) - Lactose = Glucose + Galactose (milk sugar) 3. Polysaccharides (Many sugar units): - Polymers of monosaccharides linked by glycosidic bonds - Examples: - Starch: Plant storage polysaccharide (amylose + amylopectin); energy reserve - Glycogen: Animal storage polysaccharide; stored in liver and muscles - Cellulose: Structural polysaccharide; plant cell wall; most abundant organic compound - Chitin: Structural polysaccharide in arthropod exoskeletons and fungal cell walls Functions of carbohydrates: - Energy source (glucose is the primary fuel) - Energy storage (starch in plants, glycogen in animals) - Structural support (cellulose in cell walls) - Component of nucleic acids (ribose in RNA, deoxyribose in DNA)

Proteins are polymers of amino acids linked by peptide bonds. There are 20 standard amino acids. Amino acid structure: Each amino acid has an amino group (−NH₂), a carboxyl group (−COOH), a hydrogen atom, and a variable R group (side chain) attached to a central carbon (alpha carbon). Classification based on structure: 1. Primary structure: Sequence of amino acids in a polypeptide chain, linked by peptide bonds. It determines the protein's identity and function. 2. Secondary structure: Regular, repeated folding of the polypeptide chain, stabilised by hydrogen bonds. - Alpha-helix: Coiled, right-handed spiral (e.g., keratin) - Beta-pleated sheet: Extended, sheet-like arrangement (e.g., silk fibroin) 3. Tertiary structure: Three-dimensional folding of the polypeptide chain, stabilised by: - Disulphide bonds (S–S bonds between cysteine residues) - Ionic bonds (between charged R groups) - Hydrogen bonds - Hydrophobic interactions 4. Quaternary structure: Association of two or more polypeptide chains (subunits). - Example: Haemoglobin has 4 subunits (2 alpha + 2 beta chains) Classification based on composition: - Simple proteins: Yield only amino acids on hydrolysis (e.g., albumin, globulin) - Conjugated proteins: Simple protein + non-protein group (prosthetic group) - Glycoproteins (protein + carbohydrate) - Lipoproteins (protein + lipid) - Nucleoproteins (protein + nucleic acid) Functions of proteins: - Enzymes (biocatalysts — e.g., amylase, catalase) - Structural (collagen, keratin) - Transport (haemoglobin — carries O₂) - Defence (antibodies/immunoglobulins) - Hormones (insulin, growth hormone) - Movement (actin, myosin)

Mechanism of Enzyme Action: 1. The substrate (S) binds to the specific active site on the enzyme (E) 2. Forms an enzyme-substrate complex (ES) 3. The enzyme catalyses the conversion of substrate to product (P) 4. The product is released, and the enzyme is free to bind another substrate Formula: E + S → ES → E + P Models of Enzyme Action: - Lock and Key Model (Fischer): Active site is rigid; substrate fits like a key in a lock - Induced Fit Model (Koshland): Active site is flexible; it changes shape to accommodate the substrate Factors Affecting Enzyme Activity: 1. Temperature: - Enzyme activity increases with temperature up to an optimum (usually 35–40°C for human enzymes) - Above optimum, activity decreases due to denaturation (loss of 3D structure) - At 0°C, enzymes are inactive but not destroyed 2. pH: - Each enzyme has an optimum pH (e.g., pepsin = pH 2, salivary amylase = pH 6.8) - Extreme pH values denature enzymes 3. Substrate concentration: - Activity increases with substrate concentration up to a maximum (Vmax) - At Vmax, all active sites are occupied (saturation) 4. Enzyme concentration: - Activity increases with enzyme concentration (if substrate is in excess) 5. Inhibitors: - Competitive inhibitors: Compete with substrate for active site; similar structure to substrate; can be overcome by increasing substrate concentration - Non-competitive inhibitors: Bind at allosteric site; change enzyme shape; cannot be overcome by increasing substrate concentration