ENZYME KINETICS
Complete Study Guide
1. INTRODUCTION TO ENZYMES
What Are Enzymes?
Definition: Biological catalysts that speed up reactions by lowering activation energy
(ΔG‡), without being consumed or changing the equilibrium.
• Etymology: En (in) + zyme (yeast) – discovered by Edward Buchner in 1897
• Made of amino acids folded into precise 3D shapes (some RNA = ribozymes)
• Not consumed – can catalyze many reactions repeatedly
• Fast and specific – accelerate reactions up to 10¹⁷ times
• Sensitive to pH and temperature – extreme conditions denature them
Key Properties
• Lower activation energy: Make reactions faster by stabilizing the transition
state
• Do NOT change: Free energy (ΔG) or equilibrium position – only speed up
reaching equilibrium
• Specificity: Each enzyme works on specific substrates (like a lock and key)
,2. COFACTORS AND COENZYMES
Definitions
• Cofactor: Non-protein helper required for enzyme activity (metals or organic
molecules)
• Apoenzyme: Inactive enzyme without its cofactor
• Holoenzyme: Active enzyme WITH cofactor bound (apoenzyme + cofactor =
holoenzyme)
Metal Cofactors (Key Exam Focus)
Metal Ion Role Key Enzyme Example
Stabilizes ATP
Hexokinase, DNA
Mg²⁺ phosphates, essential for
polymerase, kinases
ATP-dependent reactions
Catalytic and structural Carbonic anhydrase,
Zn²⁺
role, polarizes water alcohol dehydrogenase
Electron transfer in redox
Fe²⁺/Fe³⁺ Cytochromes, hemoglobin
reactions
Electron transfer in Cytochrome c oxidase,
Cu²⁺
oxidation-reduction superoxide dismutase
Activates enzymes, redox
Mn²⁺ Mn-SOD, photosystem II
reactions
🎯 EXAM TIP: Mg²⁺ is essential for enzymes working with ATP!
Key Coenzymes (Electron Carriers)
Coenzyme Main Role Key Pathway
Electron carrier in redox
NAD⁺/NADH Glycolysis, TCA cycle
reactions
Electron and hydrogen TCA cycle (succinate →
FAD/FADH₂
carrier fumarate)
Transfers acyl groups (–
Coenzyme A (CoA) Pyruvate → Acetyl-CoA
CO–R)
TPP Transfers aldehyde groups Pyruvate dehydrogenase
, THF Carries one-carbon units Nucleotide synthesis
🎯 MEMORIZE: NAD⁺ is THE primary electron carrier in catabolic reactions!
Complete Study Guide
1. INTRODUCTION TO ENZYMES
What Are Enzymes?
Definition: Biological catalysts that speed up reactions by lowering activation energy
(ΔG‡), without being consumed or changing the equilibrium.
• Etymology: En (in) + zyme (yeast) – discovered by Edward Buchner in 1897
• Made of amino acids folded into precise 3D shapes (some RNA = ribozymes)
• Not consumed – can catalyze many reactions repeatedly
• Fast and specific – accelerate reactions up to 10¹⁷ times
• Sensitive to pH and temperature – extreme conditions denature them
Key Properties
• Lower activation energy: Make reactions faster by stabilizing the transition
state
• Do NOT change: Free energy (ΔG) or equilibrium position – only speed up
reaching equilibrium
• Specificity: Each enzyme works on specific substrates (like a lock and key)
,2. COFACTORS AND COENZYMES
Definitions
• Cofactor: Non-protein helper required for enzyme activity (metals or organic
molecules)
• Apoenzyme: Inactive enzyme without its cofactor
• Holoenzyme: Active enzyme WITH cofactor bound (apoenzyme + cofactor =
holoenzyme)
Metal Cofactors (Key Exam Focus)
Metal Ion Role Key Enzyme Example
Stabilizes ATP
Hexokinase, DNA
Mg²⁺ phosphates, essential for
polymerase, kinases
ATP-dependent reactions
Catalytic and structural Carbonic anhydrase,
Zn²⁺
role, polarizes water alcohol dehydrogenase
Electron transfer in redox
Fe²⁺/Fe³⁺ Cytochromes, hemoglobin
reactions
Electron transfer in Cytochrome c oxidase,
Cu²⁺
oxidation-reduction superoxide dismutase
Activates enzymes, redox
Mn²⁺ Mn-SOD, photosystem II
reactions
🎯 EXAM TIP: Mg²⁺ is essential for enzymes working with ATP!
Key Coenzymes (Electron Carriers)
Coenzyme Main Role Key Pathway
Electron carrier in redox
NAD⁺/NADH Glycolysis, TCA cycle
reactions
Electron and hydrogen TCA cycle (succinate →
FAD/FADH₂
carrier fumarate)
Transfers acyl groups (–
Coenzyme A (CoA) Pyruvate → Acetyl-CoA
CO–R)
TPP Transfers aldehyde groups Pyruvate dehydrogenase
, THF Carries one-carbon units Nucleotide synthesis
🎯 MEMORIZE: NAD⁺ is THE primary electron carrier in catabolic reactions!
