Answer to Question #312316 in Biochemistry for shh

Question

 If carbohydrates are unavailable for cellular respiration, other organic molecules can be broken down and enter the cellular respiration process at the appropriate spot. Proteins can be broken down into a variety of amino acids. Some amino acids can be converted into glutamate which can then be converted into alpha-ketoglutarate. State which steps of the cellular respiration pathway, lead to the generation of the energy molecules. State the TOTAL number of ATP molecules the ONE of these converted alpha-ketoglutarate molecules can produce and explain how all the ATP molecules are generated.

Answer 1

7.5 or roughly 8 ATP, 1 from substrate-level phosphorylation (GTP to ATP) and 6.5 or roughly 7 from oxidative phosphorylation (NADH and FADH2 going through the electron transport chain).

Looking at the Krebs cycle (also known as the citric acid cycle), you can pinpoint where alpha-ketoglutarate comes in. See the attached image to follow the cycle. After alpha-ketoglutarate is introduced, you can see that from this point onward, 2 NADH, 1 GTP, and 1 FADH2 are produced, before the cycle starts over again with a new molecule of the starting material (acetyl coA). To understand the total number of ATP generated from this one molecule of alpha-ketoglutarate, we have to think about where each of these molecules end up and why they're important:

• The 1 GTP is converted to 1 ATP, through substrate-level phosphorylation during the Krebs cycle
• Every molecule of NADH yields about 2.5 ATP through oxidative phosphorylation, via the electron transport chain (ETC), so here 2 molecules of NADH will yield 5 ATP
• Every molecule of FADH2 yields about 1.5 ATP through oxidative phosphorylation via the ETC, so here 1 molecule of FADH2 will yield 1.5 ATP, or 2 ATP if you want to round up

So, in total, one molecule of converted alpha-keotglutarate will yield 1 + 5 + 1.5 = 7.5 or roughly 8 molecules of ATP.

To answer the question of which steps of the cellular respiration pathway lead to the generation of energy molecules, it's important to realize that all the steps do, to an extent. Glycolysis yields 2 ATP by substrate-level phosphorylation, the Krebs cycle produces 2 ATP via substrate-level phosphorylation, and both those steps plus the oxidation of pyruvate create electron carriers (NADH and FADH2) to fuel the ETC, which generates 26-28 ATP. This gives a total of 30-32 ATP overall from cellular respiration.