BI2.1-5 | Enzyme — Summary & Reflection

REFLECT

Think about these questions and write 3–4 sentences for each:

1. Enzyme in your daily life: You ate your last meal several hours ago. Name three classes of digestive enzymes that broke down that food (think: carbohydrates, proteins, fats). Which IUBMB class does each belong to?
2. Km in action: Your cells have two enzymes that can phosphorylate glucose: hexokinase (Km = 0.1 mM) and glucokinase (Km = 10 mM). Based on their Km values, which enzyme works at normal blood glucose levels? Which one only 'kicks in' when blood glucose is very high (e.g., after a meal)? What organ do you think glucokinase is found in? (Hint: it's the organ that 'senses' high blood glucose.)
3. Drug design: If you were designing a drug to block a specific enzyme, would you choose a competitive or non-competitive inhibitor? What are the advantages and disadvantages of each approach?

KEY TAKEAWAYS

Key takeaways — your study checklist:

1. Enzymes are biological catalysts (mostly proteins) that lower activation energy. They are specific, efficient, and regulated. Holoenzyme = apoenzyme + cofactor. Coenzymes are derived from vitamins (BI2.1).
2. Isoenzymes are different forms of the same enzyme in different tissues. LDH (5 types) and CK (3 types) are the most clinically important. LDH1 > LDH2 = heart damage; CK-MB = cardiac marker (BI2.1).
3. IUBMB classification: 6 classes — Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases. Mnemonic: "Over The Hill, Liz Is Lazy" (BI2.1).
4. Active site models: Lock-and-key (rigid) vs Induced fit (flexible, currently accepted). Enzymes are affected by temperature, pH, substrate concentration, and inhibitors (BI2.2).
5. Km and Vmax: Vmax = maximum rate at saturation. Km = [S] at ½Vmax. Low Km = high affinity. These are the two most important numbers in enzyme kinetics (BI2.2).
6. Inhibition: Competitive (active site, ↑Km, Vmax same; e.g., statins). Non-competitive (allosteric site, Km same, ↓Vmax). Irreversible (permanent; e.g., aspirin on COX). Many drugs are enzyme inhibitors (BI2.3).
7. Clinical enzymes: Troponin + CK-MB = MI. ALT/AST = liver. ALP + GGT = biliary. Lipase = pancreatitis. De Ritis ratio: <1 = viral hepatitis, >2 = alcoholic liver disease (BI2.4, BI2.5).