📖 Notes LESSON 04 OF 17

How Enzymes Actually Work

⏱️ 30 min

🧬 Biology

How Enzymes Actually Work

Enzyme kinetics, the difference between competitive and non-competitive inhibition, and the environmental factors that speed up or shut down enzyme activity.

Fundamentals

Enzymes as Biological Catalysts

Enzymes are proteins that act as biological catalysts
They lower the activation energy of a reaction
Each enzyme is substrate-specific
Enzymes are not consumed in the reaction

Kinetics — Vmax and Km

Vmax = the maximum reaction velocity
Km = substrate concentration [S] at half of Vmax
A low Km means high affinity — a "good" enzyme for that substrate

Competitive vs Non-Competitive Inhibition

Inhibition Comparison

REFERENCE

COMPETITIVE INHIBITION:
  Binds the active site
  Increasing [S] can overcome it
  Vmax unchanged, Km increases

NON-COMPETITIVE INHIBITION:
  Binds an allosteric site (not the active site)
  Increasing [S] does NOT overcome it
  Vmax decreases, Km unchanged

Factors Affecting Enzyme Activity

Temperature: optimum ~37°C for human enzymes
pH optimum varies by enzyme: pepsin (2, stomach), amylase (7, saliva), trypsin (8, small intestine)

🧪 Optimum pH by Enzyme

Pepsin (stomach)

pH 2

Amylase (saliva)

pH 7

Trypsin (intestine)

pH 8

💡

Exam tip

MDCAT loves to show a Michaelis-Menten-style graph and ask you to identify whether Vmax or Km changed. Memorise which one moves for each inhibition type rather than the graph shapes.

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