Exercises: Lipid and protein catabolism

Explain what β-oxidation is, where in the cell it occurs, and what product it feeds into the Krebs cycle. State also which electron-carrier molecules are generated during the process.

Order the three types of energy biomolecules (carbohydrates, lipids, and proteins) according to the energy they provide per gram, and explain why the body preferentially uses carbohydrates and turns to proteins only in extreme situations.

Before being oxidized, fatty acids must be activated by binding to coenzyme A. Explain what coenzyme A is and what general role it plays as a carrier of acyl groups in metabolism.

Where are reserve fats stored in the body? Explain what happens in adipose tissue when the body needs energy (lipolysis) and which molecules are then released into the blood.

The amino acids of ingested proteins can follow three fates: building new proteins, being transformed into other nitrogenous molecules, or being broken down to obtain energy. Explain them briefly and state which one takes priority when the diet is balanced.

In β-oxidation, fatty acids are shortened by two carbon atoms at a time. Explain why it receives that name (on which carbon of the chain the oxidation occurs) and what fragment is released in each round of the process.

Explain why 1 g of fat yields more ATP than 1 g of glucose, referring to the degree of reduction of the carbons in the hydrocarbon chain of fatty acids and the quantity of electrons they can donate to the respiratory chain.

A saturated fatty acid with $18$ carbon atoms is completely degraded by β-oxidation. Calculate how many rounds of β-oxidation are needed and how many acetyl-CoA molecules are obtained, explaining your reasoning for the calculation.