Biochemistry Lecture Notes: Krebs Cycle and Related Topics

Overview of the Lecture

• Focus on understanding the Krebs cycle.
• Importance of repetition and storytelling to memorize pathways (e.g., starting from phenylalanine or glucose).

Case Study

• Patient Scenario: 52-year-old homeless male, suspected withdrawal seizures, elevated gamma-glutamyl transferase (GGT).
• Key Point: Importance of knowing the Krebs cycle and its basics.
• Important Enzymes: Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.
• Cofactors Needed: Thiamine, lipoic acid, pantothenic acid, FAD, NAD.

Memorization Tips

• Acronym: "Citrate is Krebs' Starting Substrate For Making Oxaloacetate."
  • Key steps to remember involve decarboxylation and energy production.
• Key Steps:
  • Isocitrate to alpha-ketoglutarate (rate-limiting step): Influenced by NADH, ATP, ADP, and AMP.
  • Alpha-ketoglutarate step: Requires cofactors (thiamine, etc.).
  • Succinyl-CoA to succinate: Produces GTP.
  • Production of FADH2 for electron transport.

Alcohol Withdrawal and Biochemistry

• Deficiencies: B1 (Thiamine) often deficient in alcoholics.
• Associated Conditions: Wernicke-Korsakoff syndrome (confusion, ophthalmoplegia, ataxia).
• Test Questions Insight: Often involve B1 as a cofactor for key steps.

Maple Syrup Urine Disease (MSUD)

• Symptoms: Lethargic newborn with sweet odor in urine.
• Deficiency: Alpha-keto acid dehydrogenase defective, affecting branched-chain amino acids (isoleucine, leucine, valine).
• Dietary Restriction: Focus on restricting leucine.

Starvation and Krebs Cycle

• Reaction: Conversion of pyruvate to phosphoenolpyruvate during starvation.
• Source of Energy: GTP produced in the Krebs cycle.

Key Learnings

• Krebs Cycle Steps: Understand and memorize key four steps for biochemistry questions.
• Integration: Connect pathways from phenylalanine to glucose through the Krebs cycle.

Concluding Remarks

• Study Strategy: Emphasize the narrative of pathways for effective memorization and application.
• Important Points: Focus on rate-limiting steps, cofactor dependencies, and energy production aspects of the Krebs cycle.