Enzymes, Krebs Cycle & ATP ̶ Study Notes
Catabolism & Anabolism
• Catabolism: Breakdown of molecules with energy release (energetically favourable).
• Anabolism: Biosynthesis of molecules requiring energy from carrier molecules.
Key takeaway: Catabolism releases energy; Anabolism consumes it.
Oxidation & Reduction (OILRIG)
• Occur simultaneously ̶ no net electron change overall.
• One chemical is oxidised (loses e ), another is reduced (gains e ).
Key takeaway: Oxidation Is Loss, Reduction Is Gain ̶ always paired.
Enzymes
• Biological catalysts that lower activation energy.
• Remain unaltered and are highly specific.
ATP (Adenosine Triphosphate)
• Three phosphates linked by high-energy phosphoanhydride bonds.
• Hydrolysis releases energy.
• Acts as an activated carrier molecule.
Key takeaway: ATP stores energy in phosphate bonds ̶ the cell s energy currency.
Krebs Cycle (Citric Acid Cycle)
• Occurs in mitochondrial matrix.
• Produces NADH, FADH₂, and GTP (energy equivalents).
• CO₂ released as by-product.
Key takeaway: Krebs Cycle oxidises acetyl-CoA to supply high-energy electrons.
Oxidative Phosphorylation (Electron Transport Chain)
• Occurs in cristae of mitochondria.
• Produces ˜3 ATP per O₂ molecule.
• Involves four main protein complexes and ATP synthase.
Complex Name Function
I NADH-Coenzyme Q Reductase Transfers e from NADH to CoQ
II Succinate-Coenzyme Q Reductase Transfers e from FADH₂ to CoQ
III Coenzyme Q-Cytochrome C Reductase Transfers e from CoQ to Cytochrome C
IV Cytochrome C Oxidase Transfers e from Cytochrome C to O₂
V ATP Synthase Uses proton flow to generate ATP
Inhibitors of OP: Oligomycin (ATP synthase blocker), Dinitrophenol (uncoupler), Rotenone (Complex I),
Cyanide (Complex IV).
Key takeaway: OP uses redox energy to pump protons and make ATP ̶ disrupted by poisons or uncouplers.
Reactive Oxygen Species (ROS) & Oxidative Stress
• ROS are highly reactive molecules that can damage cells but also aid immune defense (e.g., neutrophils
killing bacteria).
• Oxidative stress: Cellular damage from excess ROS.
Key takeaway: ROS are double-edged ̶ vital for defense, harmful in excess.
Catabolism & Anabolism
• Catabolism: Breakdown of molecules with energy release (energetically favourable).
• Anabolism: Biosynthesis of molecules requiring energy from carrier molecules.
Key takeaway: Catabolism releases energy; Anabolism consumes it.
Oxidation & Reduction (OILRIG)
• Occur simultaneously ̶ no net electron change overall.
• One chemical is oxidised (loses e ), another is reduced (gains e ).
Key takeaway: Oxidation Is Loss, Reduction Is Gain ̶ always paired.
Enzymes
• Biological catalysts that lower activation energy.
• Remain unaltered and are highly specific.
ATP (Adenosine Triphosphate)
• Three phosphates linked by high-energy phosphoanhydride bonds.
• Hydrolysis releases energy.
• Acts as an activated carrier molecule.
Key takeaway: ATP stores energy in phosphate bonds ̶ the cell s energy currency.
Krebs Cycle (Citric Acid Cycle)
• Occurs in mitochondrial matrix.
• Produces NADH, FADH₂, and GTP (energy equivalents).
• CO₂ released as by-product.
Key takeaway: Krebs Cycle oxidises acetyl-CoA to supply high-energy electrons.
Oxidative Phosphorylation (Electron Transport Chain)
• Occurs in cristae of mitochondria.
• Produces ˜3 ATP per O₂ molecule.
• Involves four main protein complexes and ATP synthase.
Complex Name Function
I NADH-Coenzyme Q Reductase Transfers e from NADH to CoQ
II Succinate-Coenzyme Q Reductase Transfers e from FADH₂ to CoQ
III Coenzyme Q-Cytochrome C Reductase Transfers e from CoQ to Cytochrome C
IV Cytochrome C Oxidase Transfers e from Cytochrome C to O₂
V ATP Synthase Uses proton flow to generate ATP
Inhibitors of OP: Oligomycin (ATP synthase blocker), Dinitrophenol (uncoupler), Rotenone (Complex I),
Cyanide (Complex IV).
Key takeaway: OP uses redox energy to pump protons and make ATP ̶ disrupted by poisons or uncouplers.
Reactive Oxygen Species (ROS) & Oxidative Stress
• ROS are highly reactive molecules that can damage cells but also aid immune defense (e.g., neutrophils
killing bacteria).
• Oxidative stress: Cellular damage from excess ROS.
Key takeaway: ROS are double-edged ̶ vital for defense, harmful in excess.
