Key Metabolic Pathways and Biochemical Processes

Ketogenesis

Ketogenesis is the biochemical process by which ketone bodies are produced as a result of fatty acid breakdown.

Phase 1: Acetoacetyl-CoA Formation

Acetyl-CoA + Acetyl-CoA → Acetoacetyl-CoA

Phase 2: HMG-CoA Synthesis

Acetoacetyl-CoA + Acetyl-CoA + H₂O → Hydroxymethylglutaryl-CoA (HMG-CoA)

Phase 3: Ketone Body Production

Hydroxymethylglutaryl-CoA (HMG-CoA) → Acetoacetate → Acetone AND β-Hydroxybutyrate

Deamination of Amino Acids

Deamination is the removal of an amino group from an amino acid.

Non-Oxidative Deamination

Serine Complex Unstable → Imino Acid → Pyruvic Acid + Ammonia (NH₃)

Oxidative Deamination

Amino Acid (AA) → Imino Acid → Keto Acid + Ammonia (NH₃)

Glycolysis

Glycolysis is the metabolic pathway that converts glucose into pyruvate, releasing energy.

Phase 1: Energy Investment Phase

• Phosphorylation: Glucose → Glucose 6-Phosphate (G6P)
• Isomerization: Glucose 6-Phosphate (G6P) → Fructose 6-Phosphate (F6P)
• Phosphorylation: Fructose 6-Phosphate (F6P) → Fructose 1,6-Bisphosphate (F1,6BP)
• Cleavage: Fructose 1,6-Bisphosphate (F1,6BP) → Glyceraldehyde 3-Phosphate (G3P) AND Dihydroxyacetone Phosphate (DHAP)
• Isomerization: Dihydroxyacetone Phosphate (DHAP) → Glyceraldehyde 3-Phosphate (G3P)

Phase 2: Energy Payoff Phase

• Oxidation and Phosphorylation: Glyceraldehyde 3-Phosphate (G3P) → 1,3-Bisphosphoglycerate
• Dephosphorylation: 1,3-Bisphosphoglycerate → 3-Phosphoglycerate
• Isomerization: 3-Phosphoglycerate → 2-Phosphoglycerate
• Dehydration: 2-Phosphoglycerate → Phosphoenolpyruvate (PEP)
• Oxidation and Dephosphorylation: Phosphoenolpyruvate (PEP) → Pyruvic Acid

Lipogenesis (6 Steps)

Lipogenesis is the process of synthesizing fatty acids and triglycerides.

1. Glycerol 3-Phosphate (G3P) → Acylglycerol 3-Phosphate
2. Dihydroxyacetone Phosphate (DHAP) → 1-Acyldihydroxyacetone Phosphate
3. Isomerization: 1-Acyldihydroxyacetone Phosphate → Acylglycerol 3-Phosphate
4. Incorporation of 1st and 2nd Acyl-CoA: Acylglycerol 3-Phosphate → Phosphatidic Acid
5. Dephosphorylation: Phosphatidic Acid → 1,2-Diacylglycerides
6. Incorporation of 3rd Acyl-CoA: 1,2-Diacylglycerides → Triglycerides

Pentose Phosphate Pathway (5 Steps)

The Pentose Phosphate Pathway (PPP) produces NADPH and pentose sugars.

1. Glucose 6-Phosphate (G6P) → 6-Phosphogluconolactone
2. 6-Phosphogluconolactone → 6-Phosphogluconate
3. 6-Phosphogluconate → 3-Keto-6-Phosphogluconate
4. 3-Keto-6-Phosphogluconate → Ribulose 5-Phosphate
5. Ribulose 5-Phosphate → Epimerization → Xylulose 5-Phosphate
   → Isomerization → Ribose 5-Phosphate

Transamination of Amino Acids

Transamination is the transfer of an amino group from an amino acid to a keto acid.

• Amino Acid ↔ Keto Acid
• Keto Acid ↔ Amino Acid

Glutamic-Oxaloacetic Transaminase (GOT)

• Amino Acid ↔ Keto Acid
• α-Ketoglutarate ↔ Glutamate
• Oxaloacetate ↔ Aspartate

Glutamic-Pyruvic Transaminase (GPT)

• Amino Acid ↔ Keto Acid
• Pyruvate ↔ Alanine
• α-Ketoglutarate ↔ Glutamate

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa) in biological and chemical systems.

The curve illustrates the buffering capacity, where the area with a greater slope indicates more effective buffering. This represents the relationship between the ratio of conjugate base to weak acid and pH relative to its pKa, where pH variation is minimal.

Acid Form

pH = pKa + log [A⁻] / [HA]

Base Form

pOH = pKb + log [BH⁺] / [B]