Cellular Respiration Overview

Definition

• Cellular respiration: process of deriving energy from food.
• Reaction: C₆H₁₂O₆ (glucose) + 6 O₂ → 6 CO₂ + 6 H₂O + energy.
• Exergonic: releases energy; part captured as ATP.

ATP Basics

• ATP (Adenosine Triphosphate): Energy currency of the cell.
  • Drives endergonic reactions via phosphate group transfer.
  • Conversion process: ADP + energy → ATP.
  • Breakdown: ATP → ADP + Pi, releasing energy (exergonic).
• Cells use ATP for efficiency to minimize energy loss as heat.

Cellular Respiration Stages

1. Glycolysis

   • Occurs in the cytosol.
   • Glucose (6C) → 2 Pyruvate (3C each).
   • Produces 2 ATP (net) through substrate-level phosphorylation and 2 NADH.

2. Pyruvate Oxidation

   • Pyruvate → Acetyl CoA.
   • Occurs in the mitochondria.
   • Produces NADH, releases CO₂.

3. Krebs Cycle (Citric Acid Cycle)

   • Acetyl CoA → CO₂.
   • Occurs in the mitochondrial matrix.
   • Produces: 3 NADH, 1 FADH₂, 1 ATP (per acetyl CoA).

4. Electron Transport Chain (ETC) and Chemiosmosis

   • Occurs in the inner mitochondrial membrane.
   • Uses NADH and FADH₂ to produce ATP.
   • Oxygen is the final electron acceptor forming water.
   • ATP produced via oxidative phosphorylation.

Enzymatic Functions

• Kinase: transfers phosphate groups.
• Dehydrogenase: transfers hydrogen atoms.
• Isomerase: catalyzes rearrangement reactions.

Efficiency of ATP Production

• Total ATP Yield:
  • Glycolysis: 2 ATP (net), 2 NADH → ~4-6 ATP.
  • Pyruvate Oxidation: 2 NADH → ~6 ATP.
  • Krebs Cycle: 2 ATP, 6 NADH → ~18 ATP, 2 FADH₂ → ~4 ATP.
  • Total Maximum: ~36-38 ATP (ideal condition).

Anaerobic Respiration

• Lactic Acid Fermentation:

  • Occurs in muscle cells without oxygen.
  • Pyruvate → Lactate; regenerates NAD⁺.
  • Net gain: 2 ATP per glucose.

• Ethanol Fermentation:

  • Occurs in yeast.
  • Pyruvate → Acetaldehyde → Ethanol.
  • Produces CO₂ and regenerates NAD⁺.

Mitochondrial Structure

• Outer membrane, inner membrane, intermembrane space, mitochondrial matrix.
• Electron transport chain is in the inner membrane.

Key Concepts

• Redox Reactions:
  • Oxidation: loss of electrons.
  • Reduction: gain of electrons.
• Oxygen is the final electron acceptor, driving the electron transport chain.
• Proton gradient drives ATP synthesis in chemiosmosis.

Practice Questions Summary

• Products of cellular respiration include CO₂, H₂O, ATP, and heat.
• Glycolysis yields 2 ATP.
• Lactic acid fermentation occurs in anaerobic conditions in muscles.
• Pyruvate oxidation produces CO₂ and NADH.
• Electron transport chain ends with the formation of water.
• Krebs cycle regenerates oxaloacetate and produces CO₂, NADH, FADH₂, and ATP.