Cellular Respiration

Respiration is a biological process that converts food into energy through metabolic pathways.

Mitochondrion Structure:
- The mitochondrion is comprised of:
  - Outer Membrane: Surrounds the mitochondrion.
  - Inner Membrane: Contains the electron transport chain and ATP synthase.
  - Intermembrane Space: Between the inner and outer membranes.
  - Matrix: Contains enzymes for reactions of the citric acid cycle.
**Key Molecules Involved: **
- ADP: Adenosine diphosphate, is converted to ATP through phosphorylation.
- Acetate: A two-carbon molecule formed from the breakdown of glucose, which enters the citric acid cycle by combining with oxaloacetate.
- NADH: Nicotinamide adenine dinucleotide (reduced form); carries electrons to the electron transport chain.
- Oxygen: The final electron acceptor in aerobic respiration.
- ATP: Adenosine triphosphate; the primary energy currency of the cell.

Glycolysis:
- Occurs in the cytosol.
- Converts glucose (6-carbons) to two molecules of pyruvate (3-carbons).
- Generates a small amount of ATP via substrate-level phosphorylation.
Citric Acid Cycle (Krebs Cycle):
- Occurs in the mitochondrial matrix.
- Involves the conversion of Acetyl-CoA into CO₂ and processes several reducing agents (NADH, FADH₂).
- Each turn produces 1 ATP, 3 NADH, and 1 FADH₂.
Electron Transport Chain (ETC):
- Located in the inner membrane of mitochondria.
- Composed of protein complexes that pump protons into the intermembrane space, creating a proton motive force.
- ATP synthase uses this proton gradient to synthesize ATP during oxidative phosphorylation.
- The complexes that actively transport protons are I, III, and IV.
Oxidative Phosphorylation:
- Process of ATP formation using the electrochemical gradient created by the electron transport chain.
- Each NADH produces about 2.5 ATP (6 protons pumped) and FADH₂ produces around 1.5 ATP (4 protons pumped).

Total ATP Yield from One Glucose Molecule:
- Under aerobic conditions, a maximum of around 30-32 ATP can be produced per glucose molecule.
- Includes:
  - Glycolysis: 2 ATP from substrate-level phosphorylation.
  - Krebs Cycle: 2 ATP from substrate-level phosphorylation.
  - Oxidative Phosphorylation: Approximately 26-28 ATP from NADH and FADH₂.

Definition: A metabolic process that converts sugar to acids, gases, or alcohol in anaerobic conditions.
Types of Fermentation:
- Alcoholic Fermentation:
- Produces ethanol and carbon dioxide from glucose.
- Lactic Acid Fermentation:
- Occurs in muscle cells under anaerobic conditions, producing lactic acid and regenerating NAD+.

Understanding respiration is crucial for fields such as medicine, exercise science, and bioengineering.
Applications include enhancing athletic performance through metabolic training and developing therapies for metabolic diseases.

Manipulation of metabolic pathways can raise ethical questions in biotechnology and medicine, particularly concerning genetic modifications and their impact on health.

Substrate-Level Phosphorylation: Direct transfer of a phosphate group to ADP to form ATP during glycolysis and the citric acid cycle.
Proton Motive Force: The potential energy stored in the proton gradient across the inner mitochondrial membrane, used to drive ATP synthesis.

Proton Motive Force Locations:
- Hydrogen ions are pumped into the intermembrane space by electron transport complex proteins I, III, and IV.
Final Electron Acceptor: Oxygen, essential for efficient ATP production in aerobic respiration.
Net ATP Yield of Glycolysis:
- Prior to pyruvate entering the citric acid cycle, glycolysis directly results in 2 ATP through substrate-level phosphorylation.
Net ATP Yield from Citric Acid Cycle:
- From the complete oxidation of glucose, the cycle yields a net of 2 ATP per glucose molecule used through substrate-level phosphorylation.
Enzyme Mechanism in ATP Synthesis:
- ATP Synthase employs a rotor mechanism to synthesize ATP, energy derived from the flow of protons back into the mitochondrial matrix.