Study guides › B/B › Biochemistry
Lipid & Amino Acid Metabolism, Hormonal Regulation
Cells burn fat and protein as well as sugar. You will follow fatty acid oxidation, ketone bodies, fatty acid and cholesterol synthesis, amino acid disposal and the urea cycle, then see how insulin, glucagon, epinephrine and cortisol steer each organ through fed and fasting states.
Study this chapter in PrepMed (free)
What this chapter covers
- Fatty Acid Oxidation and Ketone Bodies. Beta-oxidation is a repeating four-step cycle, and ketone bodies are what the liver makes when acetyl-CoA piles up.
- Fatty Acid and Cholesterol Synthesis. Fat synthesis is not just beta-oxidation in reverse: it happens in a different compartment, with different carriers and cofactors.
- Amino Acid Catabolism and the Urea Cycle. Amino nitrogen must be removed safely and the carbon skeletons routed into the fuel pathways; the urea cycle steps are testable.
- Hormonal Regulation of Metabolism. Every regulatory-enzyme question comes down to which hormone is present and whether it adds or removes a phosphate.
- Fed vs Fasting States and Organ-Specific Metabolism. Knowing which organ can use which fuel, and which hormone dominates when, answers most integrative metabolism questions.
Key points to know
- Beta-oxidation: acyl-CoA DH (FAD), hydratase, 3-hydroxyacyl-CoA DH (NAD⁺), thiolase
- CPT-I is the control point and is blocked by malonyl-CoA
- Synthesis: citrate shuttle, ACC (biotin) to malonyl-CoA, fatty acid synthase, palmitate (16:0)
- ACC is activated by insulin and citrate and inhibited by glucagon, epinephrine, and palmitoyl-CoA
- Transamination uses PLP (B₆); glutamate carries nitrogen to the liver
- Nitrogen travels as glutamine and alanine
- Insulin (fed): dephosphorylation, storage. Glucagon (fasting): cAMP and PKA, release
- Glucagon acts on liver and fat, not on muscle
Try a practice question
Which enzyme of beta-oxidation generates NADH?
- Acyl-CoA dehydrogenase
- Enoyl-CoA hydratase
- 3-Hydroxyacyl-CoA dehydrogenase
- Thiolase
Show the answer
C. 3-Hydroxyacyl-CoA dehydrogenase oxidizes the hydroxyl to a ketone with NAD⁺. Acyl-CoA dehydrogenase makes FADH₂, the hydratase adds water, and thiolase cleaves with CoA.
Common questions
What does this chapter cover?
Lipid & Amino Acid Metabolism, Hormonal Regulation covers Fatty Acid Oxidation and Ketone Bodies, Fatty Acid and Cholesterol Synthesis, Amino Acid Catabolism and the Urea Cycle, Hormonal Regulation of Metabolism, Fed vs Fasting States and Organ-Specific Metabolism.
What should I know first?
Beta-oxidation: acyl-CoA DH (FAD), hydratase, 3-hydroxyacyl-CoA DH (NAD⁺), thiolase CPT-I is the control point and is blocked by malonyl-CoA Synthesis: citrate shuttle, ACC (biotin) to malonyl-CoA, fatty acid synthase, palmitate (16:0)
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.