Detailed Study Notes on the Citric Acid Cycle and Electron Transport Chain

The processes of glucose oxidation and cellular respiration are crucial for ATP synthesis.
- Glycolysis: Breakdown of glucose to pyruvate.
- Pyruvate Oxidation: Conversion of pyruvate to acetyl-CoA.
- Citric Acid Cycle (CAC): Further breakdown of acetyl-CoA.
- Oxidative Respiration: Utilization of the electron transport chain for ATP production.

% Fermentation vs Cellular Respiration:
- O2 present: Pyruvate is converted into acetyl-CoA, CO2, and H2O, facilitates the Citric Acid Cycle.
- O2 absent: Pyruvate undergoes fermentation, resulting in lactate (in muscles) or alcohol (in yeast).
Fate of Pyruvate:
- In aerobic conditions (presence of O2):
- Pyruvate is utilized in the citric acid cycle.
- NAD+ is regenerated from NADH for glycolysis continuity.
- In anaerobic conditions (absence of O2):
- Fermentation pathways convert pyruvate to lactate or alcohol.

Occurs in the mitochondrial matrix.
Generated products:
- Acetyl CoA (2C) for the Citric Acid Cycle.
- CO2 as a by-product.
- NADH (reduced from NAD+) as an electron carrier.
Enzyme involved:
- Pyruvate Dehydrogenase: Catalyzes the reaction of pyruvate oxidation.
- Reaction is: ${ ext{Pyruvate (3C)} <br>ightarrow ext{Acetyl-CoA (2C)} + ext{CO}_2}$

Intermembrane Space:
- Location for pyruvate oxidation and CAC in eukaryotes.
Membrane Structure:
- Outer Membrane: Contains porins and is permeable to small molecules.
- Inner Membrane: Folded into cristae to maximize surface area.
Matrix: Site of pyruvate oxidation and CAC reactions.

Begin with Acetyl-CoA (2C) and Oxaloacetate (OAA) (4C):
- Forming Citrate (6C).
Important Points:
- Regeneration of OAA occurs at the end of the cycle, enabling the cycle to continue.
- Carbon Loss:
- Steps involve the release of CO2.
- Pay attention to the number of carbon atoms throughout the cycle.
Key reactions:
- OAA (4C) + Acetyl-CoA (2C) → Citrate (6C).
- Steps involving NAD+ reduction to NADH showing oxidation reactions.
Summary of Energy Released:
- Glycolysis: Net 2 ATP, 2 NADH
- Pyruvate Oxidation: 2 NADH (for 2 pyruvate)
- CAC: 6 NADH, 2 FADH2, 2 GTP (converted to ATP).
Overall yield per glucose:
- 4 ATP, 10 NADH, 2 FADH2.

Main Function: ATP synthesis via oxidative phosphorylation.
Process Overview:
- Components: Protein complexes (I, II, III, IV) transfer electrons.
- Proton Gradient: Creates a high concentration of protons (H+) in the intermembrane space, leading to low pH.
- Complex II accepts electrons from FADH2 but does not pump protons.
- ATP synthase (Complex V) uses the proton gradient to produce ATP.
ATP Yield:
- NADH: approximately 2.5 ATP per electron pair.
- FADH2: approximately 1.5 ATP per electron pair.

Proposed by Peter Mitchell in 1961 and awarded Nobel Prize in 1978.
- The proton gradient from the ETC powers ATP synthesis.
- H+ ions flow from high concentration (intermembrane space) to low concentration (matrix).
ATP synthase is activated by this proton movement, driving ATP production.

Adipose Tissue:
- Stores and releases fatty acids.
- Uses glucose to synthesize glycerol, with acetyl-CoA for fatty acid production.
Liver:
- Major role in gluconeogenesis, maintaining blood glucose levels.
- Synthesizes and degrades triacylglycerols (TAGs).
Brain:
- Consumes a significant portion of body oxygen; primarily relies on glucose, but can use ketone bodies.
Muscle:
- Capable of utilizing glucose, fatty acids, and ketone bodies.
- Engages in anaerobic metabolism via the Cori cycle.