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GATE XL study materials
GATE XL study resources

GATE XL: Post-graduate Level Subjects in Science

GATE XL · Work through your exam, one topic at a time.

All guide sections

Post-graduate Level Subjects in Science

Domain scope

This domain covers postgraduate-level science subjects in GATE XL: Chemistry (P), Biochemistry (Q), Botany (R), Zoology (S), Microbiology (T), and Food Technology (U). The exam tests integrated mechanistic understanding, including structure–function, metabolic regulation, molecular genetics, physiology, microbial growth, and analytical reasoning, rather than isolated definitions.

Core rules and concepts

  • Enzyme kinetics: v = Vmax[S]/(Km + [S]). Km is the substrate concentration at half-Vmax; it is not a direct affinity constant, although lower Km usually means tighter binding. Competitive inhibitors raise apparent Km; noncompetitive inhibitors lower Vmax.
  • Metabolism is regulated by allosteric effectors, covalent modification, and gene expression. Glycolysis has three irreversible steps; gluconeogenesis bypasses them. ATP/AMP and citrate signal energy status.
  • Central dogma includes replication, transcription, translation, and exceptions such as reverse transcription, RNA editing, and prions. Mutations are classified by effect on protein and by reversion.
  • Microbial growth has lag, log, stationary, and death phases; in batch culture, μ is not constant. Selective and differential media, and Gram staining, depend on cell-envelope structure.
  • Plant and animal physiology: water potential drives water movement; stomatal control balances CO2 uptake and water loss; action potentials depend on Na+/K+ gradients and channel states.

Worked example

An enzyme has Vmax = 100 µmol min−1 mg−1 and Km = 5 mM. At [S] = 15 mM, v = 100×15/(5+15) = 75 µmol min−1 mg−1. At [S] = 5 mM, v = 50. The ratio v/Vmax = 0.75 shows the enzyme is 75% saturated. If a competitive inhibitor doubles apparent Km to 10 mM, at 15 mM v = 100×15/(10+15) = 60, not zero.

Traps

Confusing Km with Vmax; using initial-rate data after substrate depletion; ignoring pH and temperature; assuming log phase throughout batch growth; mixing competitive and noncompetitive inhibition; and treating correlation in ecology or genetics as causation.