C1.2 Cell Respiration

C1.2.1 ATP

• ATP is the molecule that distributes energy in cells

• Structure: Adenine + ribose + three phosphate groups

• Properties:

  • Soluble in water

  • stable at pH levels close to neutral

  • cannot pass freely through phospholipid bilayer

  • easily removable/reattachable third phosphate group through hydrolysis and condensation

  • hydrolysis of ATP → small amount of energy

C1.2.2 Life processes that need ATP

• Synthesizing macromolecules

  • anabolic reaction, endothermic

• Active transport

  • against concentration gradient

• cellular movement

  • changing shape of cell

C1.2.3 Energy transfers during conversions between ATP and ADP

• ATP → ADP + Pi + energy

  • Hydrolysis - addition of water to break bonds between third phosphate group

• ADP + Pi + energy→ ATP

  • Phosphorylation - remove water from ADP and add third phosphate group

• Small amount of energy released

  • ATP has more potential energy than ADP

C1.2.4 Cell Respiration for producing ATP

• Cell respiration: Uses oxygen and produces carbon dioxide

  • carbon compounds oxidized to produce ATP

  • energy used to produce ATP

• Gas exchange: oxygen enters cells through membrane while carbon dioxide exits the cells

• Living organisms require ATP to perform its activities - continuous cellular respiration

• common substrate is glucose

C1.2.5 Anaerobic vs Aerobic Respiration

• Aerobic: Glucose + oxygen → carbon dioxide + water + ATP

  • Glycolysis - Krebs Cycle - Electron Transport Chain

• Anaerobic: Glucose → Lactic acid/alcohol + carbon dioxide + ATP

  • Glycolysis - Fermentation

C1.2.6 Variables affecting rate of respiration

• Temperature, glucose/oxygen levels

• Respirometer

C1.2.7 Role of NAD

• Oxidation: Removal of electrons

• Reduction: Gaining electrons

• NAD is an electron carrier during cellular respiration

  • 2 H atoms are removed from the reduced substance

  • One splits into proton and electron

  • Electron is absorbed, cation released

  • NAD accepts the H remaining

C1.2.8 Conversion of glucose to pyruvate

• Glycolysis

  • Occurs in cytosol

  • Glucose (6C) → Pyruvate (3C)

  • Occurs in both aerobic and anaerobic respiration

  • example of metabolic pathway

1. Phosphorylation of glucose molecule

2. Lysis → 2 G3P

3. oxidation - removing hydrogen → reducing NAD+ to NADH

4. ATP formation

• Produces 2 ATP and 2 NADH

C1.2.9. Pyruvate → lactate (Anaerobic)

• pyruvate undergoes fermentation

• yeast oxidize NADH back to NAD by gaining 2H

• convert pyruvate to lactate/alcohol

• require NAD for glycolysis, will run out unless regenerated in fermentation

C1.2.10 Pyruvate → alcohol

• pyruvate decarboxylates, releases CO2 → ethanal (oxidizes NADH) → ethanol

• used in brewing and baking

C1.2.11 Oxidation and decarboxylation of pyruvate in Link Reaction

• aerobic respiration

• Link reaction occurs in mitochondrial matrix

• Decarboxylation - release CO2

• Oxidation - removing 2 electrons → accepted by NAD

• Binding of acetyl group and coenzyme A → Acetyl CoA

• 2 pyruvate → 2 acetyl CoA, 2 CO2, 2 NADH

C1.2.12 Oxidation and decarboxylation of acetyl groups in Krebs Cycle

• occurs in mitochondrial matrix

• Acetyl CoA (2C) + oxaloacetate (4C) → citrate (6C)

• decarboxylation of citrate → oxaloacetate and CO2

  • occurs twice

  • 6C → 5C → 4C

• formation of ATP, NADH and FADH2

  • NADH x3, FADH2 x1, ATPx1, H2Ox1 per cycle

• Substrate-level phosphorylation

• NADH and FADH2 carry electrons to electron transport chain

• 1 glucose: 6 NADH, 2 FADH2, 2 ATP, 4 CO2, 2 H2O

C1.2.13 Transfer of energy to electron transport chain

• occurs in intermembrane space

• only in presence of oxygen

• NADH and FADH2 are oxidized → electrons to electron carrier proteins

C1.2.14 Generation of Proton Gradient by flow of electrons

• Electrons in the chain release energy at each stage of the ETC

  • used to pump protons across the inner mitochondrial membrane (matrix → intermembrane space)

  • creates concentration gradient

C1.2.15 Chemiosmosis

• H+ ions move from matrix to intermembrane space through ATP synthase - chemiosmosis

• ATP synthase - integral protein channel

• Energy provided by proton gradient is used to synthesize ATP with ADP and Pi - oxidative phosphorylation

C1.2.16 Role of Oxygen

• Oxygen is the final electron acceptor

• Requires oxygen to accept electrons from NADH

• Formation of hydrogen helps maintain proton concentration gradient

• Total ATP: Glycolysis (2) + Krebs (2) + Oxidative Phosphorylation (34) → 38 ATP