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Monomer : Single polypeptide chain

Homodimer : Two identical protein subunits

Heterodimer : Two different protein subunits

Tetramer : Protein complex of four subunits

Quaternary structure : Spatial arrangement of multiple polypeptide chains

Secondary structure : Alpha helices and beta sheets stabilized by hydrogen bonds

🫁 Haemoglobin vs Myoglobin (VERY HIGH YIELD)

Myoglobin function : Oxygen storage in muscle

Haemoglobin function : Oxygen transport in blood

Myoglobin structure : Monomer

Haemoglobin structure : Heterotetramer (2 alpha, 2 beta chains)

Oxygen affinity : Myoglobin > Haemoglobin

Cooperative binding : Increased oxygen affinity after initial binding

Protein showing cooperativity : Haemoglobin

Allosteric protein : Haemoglobin

T state : Low oxygen affinity state

R state : High oxygen affinity state

Oxygen-binding curve of haemoglobin : Sigmoidal

Oxygen-binding curve of myoglobin : Hyperbolic

Bohr effect : Decreased oxygen affinity at low pH / high CO2

Physiological role of Bohr effect : Promotes oxygen release in tissues

Haem group : Protoporphyrin IX with Fe2+

Effect of O2 binding on Fe2+ : Fe2+ moves into haem plane

⚙ Enzymes – Core Concepts (EXAM)

Enzyme : Biological catalyst that lowers activation energy

Activation energy (ΔG‡) : Energy barrier to reach transition state

Effect of enzymes on ΔG : No change

Transition state : Highest-energy unstable intermediate

Active site : Region where substrate binds and catalysis occurs

Enzyme specificity : Due to shape and chemistry of active site

📈 Enzyme Kinetics (VERY HIGH YIELD)

Michaelis–Menten kinetics : Relationship between reaction rate and substrate concentration

Vmax : Maximum reaction rate at enzyme saturation

Km : Substrate concentration at Vmax/2

Km and affinity : Low Km = high affinity

Saturation : All enzyme active sites occupied

Shape of V vs [S] plot : Hyperbolic

📉 Lineweaver–Burk Plot (EXAM FAVOURITE)

Lineweaver–Burk plot : Double reciprocal plot (1/V vs 1/[S])

Y-intercept : 1/Vmax

X-intercept : −1/Km

Competitive inhibition effect on Km : Increases Km

Competitive inhibition effect on Vmax : No change

Effect on Lineweaver–Burk slope : Increases

🚫 Enzyme Inhibition & Regulation

Competitive inhibition : Inhibitor competes with substrate for active site

Non-competitive inhibition : Inhibitor binds away from active site

Allosteric regulation : Regulator binding causes conformational change

Covalent modification : Regulation by phosphorylation or acetylation

Example of covalent drug action : Aspirin acetylates cyclooxygenase

🔗 Cofactors (EXAM)

Cofactor : Non-protein molecule required for enzyme activity

Coenzyme : Loosely bound organic cofactor

Inorganic cofactors : Metal ions (e.g. Mg2+, Zn2+)

Apoenzyme : Enzyme without cofactor

Holoenzyme : Enzyme with cofactor bound

💊 Enzymes as Drug Targets (SHORT ANSWERS)

Why enzymes are good drug targets : Small activity change gives large product change

Statins : Competitive inhibitors of cholesterol synthesis enzymes

NSAIDs : Inhibit cyclooxygenase

Penicillin : Inhibits bacterial cell wall synthesis enzymesV