Chapter 7 Bio 1406

Chapter 9: Cellular Respiration and Fermentation

Catabolic Pathways and Production of ATP

1. Catabolic Pathway:

   • Breaks down large molecules to produce energy (ATP).

   • Examples: i. Cellular Respiration (oxygen dependent) ii. Fermentation (oxygen independent) iii. Anaerobic Respiration (prokaryotes, oxygen independent)

2. Cellular Respiration:

   • Includes glycolysis, citric acid cycle, and oxidative phosphorylation.

   • Reaction: C6H12O6+6O2→6CO2+6H2O+ATPC6​H12​O6​+6O2​→6CO2​+6H2​O+ATP

Redox Reactions: Oxidation and Reduction

1. Redox Reaction: Involves electron transfer.

   • Oxidation: Loss of electrons.

   • Reduction: Gain of electrons.

   • Example: 2H2+O2→2H2O2H2​+O2​→2H2​O

   • Reducing Agent: Electron donor.

   • Oxidizing Agent: Electron acceptor.

   • Some redox reactions transfer atoms or ions instead of electrons.

2. Cellular Respiration: Example of a redox reaction.

   • Reaction: C6H12O6+6O2→6CO2+6H2OC6​H12​O6​+6O2​→6CO2​+6H2​O

   • Glucose is oxidized, oxygen is reduced.

Stepwise Energy Harvesting from Organic Molecules

1. Cellular Respiration:

   • Glucose is oxidized to produce ATP.

   • Requires electron acceptors (e.g., O2O2​).

   • Electrons first transferred to NAD+NAD+.

   • NAD+NAD+ is a coenzyme that accepts electrons.

   • Reaction: NAD++2H→NADH+H+NAD++2H→NADH+H+

   • NADH donates electrons to the electron transport chain (ETC).

   • ETC drives ATP synthesis.

Stages of Cellular Respiration: Preview

1. Stages:

   • Glycolysis

   • Citric Acid Cycle

   • Oxidative Phosphorylation

2. ATP Production:

   • Glycolysis: 2 ATP

   • Citric Acid Cycle: 2 ATP

   • Oxidative Phosphorylation: 32-34 ATP

3. Substrate-Level Phosphorylation: ATP production by transferring a phosphate group from a substrate to ADP.

Stage 1: Glycolysis

1. Glycolysis:

   • Breaks down 1 glucose molecule into 2 pyruvate molecules.

   • Occurs in the cytoplasm.

   • Phases: Energy investment and energy payoff.

   • Does not require oxygen.

   • Summary:

     • Reactants: Glucose (6 carbons)

     • Products: 2 Pyruvate (3 carbons each)

     • ATP: 2 produced, 2 used

     • NADH: 2 produced

   • ATP produced via substrate-level phosphorylation.

Stage 2: Pyruvate Oxidation and Citric Acid Cycle

1. Pyruvate Oxidation:

   • Occurs in the mitochondrial matrix.

   • Summary:

     • Reactants: Pyruvate (3 carbons)

     • Products: Acetyl-CoA (2 carbons)

     • ATP: 0 produced

     • NADH: 1 produced

2. Citric Acid Cycle:

   • Completes breakdown of acetyl-CoA to CO2CO2​.

   • 2 turns per glucose molecule.

   • Summary (one turn):

     • Reactants: Acetyl-CoA (2 carbons)

     • Products: 2 CO2CO2​

     • ATP: 1 produced

     • NADH: 3 produced

     • FADH2: 1 produced

   • Total per glucose: 2 ATP, 6 NADH, 2 FADH2.

   • ATP produced via substrate-level phosphorylation.

Stage 3: Oxidative Phosphorylation

1. Oxidative Phosphorylation:

   • No carbons from glucose reach this stage.

   • Energy stored in NADH and FADH2.

   • Electrons donated to the ETC.

   • ETC drives ATP synthesis via chemiosmosis.

2. Electron Transport Chain (ETC):

   • Located in the inner mitochondrial membrane.

   • Components: Multiprotein complexes.

   • Electrons drop in energy levels.

   • Final electron acceptor: O2O2​, forming H2OH2​O.

   • Generates 32-34 ATP.

   • Electron transfer causes proton pumping.

3. Chemiosmosis and ATPase:

   • Protons move back across the membrane through ATP synthase.

   • ATP synthase synthesizes ATP.

   • Chemiosmosis couples proton gradient to ATP synthesis.

ATP Accounting in Cellular Respiration

1. Energy Flow:

   • Glucose → Glycolysis → Pyruvate Oxidation → Citric Acid Cycle → ETC

2. ATP Production:

   • Total: 36-38 ATP per glucose.

   • Variability due to differences in cell types and conditions.

Fermentation and Anaerobic Respiration

1. Anaerobic Respiration:

   • Occurs without oxygen.

   • ETC cannot function.

   • ATP produced via substrate-level phosphorylation.

2. Fermentation:

   • Glycolysis followed by regeneration of NAD+.

   • Types: Alcohol fermentation, Lactic acid fermentation.

   • Alcohol Fermentation: Produces ethanol and CO2CO2​.

   • Lactic Acid Fermentation: Produces lactic acid.

3. Comparison:

   • Aerobic Respiration: Uses glycolysis, O2O2​ as oxidizing agent, produces 36-38 ATP.

   • Anaerobic Respiration: Uses glycolysis, alternative oxidizing agents, produces less ATP.

   • Fermentation: Uses glycolysis, organic molecules as oxidizing agents, produces 2 ATP.

Glycolysis and the Citric Acid Cycle Connect to Other Metabolic Pathways

1. Connections:

   • Catabolic pathways degrade macromolecules.

   • Anabolic pathways build macromolecules.

   • Examples: Beta oxidation, amino acid metabolism.

Regulation of Cellular Respiration via Feedback Mechanisms

1. Feedback Inhibition:

   • Common mechanism for metabolic control.

   • Example: ATP inhibits glycolysis and citric acid cycle enzymes.

   • Regulates enzyme activity to synchronize glycolysis and citric acid cycle.