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Biochemistry 3% exam weight

Enzymology

Part of the NEET PG study roadmap. Biochemistry topic bioche-005 of Biochemistry.

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Enzymology

🟢 Lite — Quick Review (1h–1d)

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Enzymology — Key Facts for NEET PG Core: Enzymes are biological catalysts (protein); cofactors may be metal ions or organic (vitamins)

  • Classification: 6 classes — oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases
  • Mechanism: Lock-and-key or induced-fit; lowers activation energy
  • Kinetics: Michaelis-Menten — Km (substrate affinity), Vmax (max velocity)
  • Inhibition: Competitive (Km increases, Vmax unchanged), Non-competitive (Vmax decreases), Uncompetitive (both decrease) ⚡ Exam tip: Enzyme inhibition questions are frequent; remember competitive = resembles substrate

🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Enzymology — NEET PG Study Guide Concept: Enzymes are protein catalysts that speed up reactions without being consumed Classification (IUBMB):

  • Oxidoreductases: redox reactions (e.g., dehydrogenases)
  • Transferases: group transfer (e.g., transaminases)
  • Hydrolases: cleavage by H2O (e.g., proteases, lipases)
  • Lyases: cleavage without H2O (e.g., decarboxylases)
  • Isomerases: structural rearrangements (e.g., isomerases)
  • Ligases: joining molecules (e.g., synthetases) Mechanism: Active site with ES complex; induced-fit model (Koshland) Kinetics: Michaelis-Menten equation: v = Vmax[S]/(Km + [S])
  • Lineweaver-Burk plot: 1/v vs 1/[S] gives intercept at 1/Vmax and -1/Km Inhibition types:
  • Competitive: mimics substrate, increases Km, Vmax unchanged
  • Non-competitive: binds elsewhere, decreases Vmax, Km unchanged
  • Uncompetitive: binds ES complex, decreases both Km and Vmax Cofactors: Zn2+, Mg2+, Fe2+, Vitamins (B1→thiamine pyrophosphate, B2→FAD, B6→PLP)

🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Enzymology — Comprehensive NEET PG Notes Full coverage: Enzyme structure: Apoenzyme (protein) + cofactor = holoenzyme. Cofactors may be metal ions (Zn, Mg, Fe, Mn) or organic coenzymes derived from vitamins. Classification details:

  • Oxidoreductases: always involve electron transfer (dehydrogenases, oxidases, reductases)
  • Transferases: amino transfer (ALT, AST), methyl transfer; cofactor: PLP (B6)
  • Hydrolases: peptide bonds (proteases), ester bonds (lipases), glycosidic bonds (amylases)
  • Lyases: add/remove groups to form double bonds (decarboxylases, hydratases)
  • Isomerases: racemases, epimerases, mutases
  • Ligases: require ATP; synthetases, carboxylases Enzyme kinetics:
  • Michaelis-Menten: v = Vmax[S]/(Km + [S])
  • Km = [S] at half Vmax; reflects enzyme-substrate affinity
  • Turnover number: kcat = Vmax/[E]total
  • Catalytic efficiency: kcat/Km (upper limit ~10^9 M^-1s^-1 for diffusion-controlled reactions) Inhibition analysis:
  • Competitive: Lineweaver-Burk — same Y-intercept, different X-intercept (increased slope)
  • Non-competitive: different Y-intercept, same X-intercept
  • Uncompetitive: both intercepts changed (parallel lines) Allosteric regulation: Sigmoidal curve; Vmax increases (homotropic) or Km changes; cooperativity (Hb analogy) Clinical: Enzyme deficiency → inborn errors of metabolism; inhibitors as drugs (ACE inhibitors = captopril, statins = HMG-CoA reductase inhibitors)

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