Vitamins & Enzymes
World D — Polymers & Biomolecules
48.A — VITAMINS (MICRONUTRIENTS)
ADEK
BC
R48.01 Classification
- Organic compounds required in diet in small amounts to perform specific biological functions.
- Cannot be synthesized by the body in adequate amounts.
- Classified strictly by their solubility: Fat-soluble vs Water-soluble.
R48.02 Fat-Soluble Vitamins
- Stored in liver and adipose (fat) tissues. Excess can be toxic.
- A (Retinol): Vision. Deficiency = Night blindness.
- D (Calciferol): Bone health. Deficiency = Rickets.
- E (Tocopherol): Antioxidant. Protects cell membranes.
- K (Phylloquinone): Blood coagulation (clotting).
R48.03 Water-Soluble Vitamins
- Not stored in the body (except B12). Must be supplied regularly in diet. Excreted in urine.
- B-Complex: Energy metabolism and nerve function.
- C (Ascorbic Acid): Collagen synthesis. Deficiency = Scurvy (bleeding gums).
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R48.04 Coenzymes
- Many vitamins (especially B-complex) function as coenzymes.
- Non-protein organic molecules that bind to enzymes to help them catalyze reactions.
- Without the vitamin, the enzyme remains an inactive "apoenzyme".
48.B — ENZYMES (BIOCATALYSTS)
R48.05 What is an Enzyme?
- Biological catalysts that speed up biochemical reactions.
- Almost all enzymes are globular proteins.
- Highly specific: One enzyme typically catalyzes only one specific reaction.
R48.06 Activation Energy ($E_a$)
- Enzymes do NOT change the equilibrium of a reaction.
- They work by providing an alternative reaction pathway with a significantly lower Activation Energy.
- Makes the "energetic hill" much easier for reactants to climb.
-OH
-NH₂
-SH
R48.07 The Active Site
- A specific 3D pocket or cleft on the enzyme's surface.
- Lined with specific amino acid R-groups that bind the substrate.
- Where the catalytic reaction actually takes place.
LIPID
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LIPASE
R48.08 Naming & Classification
- Usually named by adding the suffix -ase to the substrate name (e.g., Maltose $\rightarrow$ Maltase).
- Classified by reaction type: Oxidoreductases (Redox), Hydrolases (Hydrolysis), Ligases (Joining bonds).
48.C — MECHANISMS & REGULATION
R48.09 Lock and Key Model
- Proposed by Emil Fischer (1894).
- Assumes the active site is a rigid, perfectly shaped "lock".
- The substrate is the "key" that fits exactly into it without any structural modification.
R48.10 Induced Fit Model
- Proposed by Daniel Koshland (1958) — the modern accepted view.
- The active site is flexible.
- Binding of the substrate induces a conformational change in the enzyme, wrapping around the substrate tightly (like a glove adapting to a hand).
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R48.11 Temperature & pH
- Enzymes have an Optimum temperature and pH where activity peaks.
- Below optimum: Kinetic energy is too low.
- Above optimum: The protein structure unwinds (Denaturation), permanently destroying the active site.
R48.12 Inhibitors
- Molecules that decrease enzyme activity.
- Competitive: Similar shape to substrate, physically blocks the active site.
- Non-competitive: Binds elsewhere (allosteric site), warping the enzyme's shape so the active site no longer works.