Use of Lipids and Amino Acids in Respiration

Overview

How glycerol and fatty acids from triglycerides enter respiration and why lipids yield more energy, how amino acids are deaminated before respiring them, and the order in which a starving mammal uses stores.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Into which two products is a triglyceride hydrolysed before it can be respired?

   Model answer

   It is hydrolysed into glycerol and fatty acids.

2. 2

   How does glycerol enter the respiratory pathway?

   Model answer

   It is phosphorylated and converted into triose phosphate, which joins glycolysis.

3. 3

   How does a fatty acid enter the respiratory pathway?

   Model answer

   In the mitochondrial matrix it is broken down step by step into two-carbon fragments that combine with coenzyme A to form acetyl coenzyme A, which enters the Krebs cycle.

4. 4

   Why does lipid yield roughly twice as much energy per gram as carbohydrate?

   Model answer

   Lipid molecules contain proportionally more hydrogen and less oxygen, so their oxidation generates more reduced NAD and FAD per gram and therefore more ATP.

5. 5

   Why does a long-chain fatty acid yield more ATP than a short-chain one?

   Model answer

   It is cut into more two-carbon fragments, giving more acetyl coenzyme A and more turns of the Krebs cycle.

6. 6

   Why must surplus amino acids be respired rather than stored?

   Model answer

   The body has no store for protein or amino acids, so any not needed for synthesis must be broken down.

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