How many ATP molecules are formed during substrate level phosphorylation in Krebs cycle when one glucose is consumed?

1. Break Down the Problem

The Krebs cycle, also known as the citric acid cycle, is a crucial metabolic pathway that generates energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. To find out how many ATP (adenosine triphosphate) molecules are formed through substrate-level phosphorylation when glucose is consumed, we need to consider the complete conversion of glucose to pyruvate during glycolysis and subsequently to acetyl-CoA that enters the Krebs cycle.

2. Relevant Concepts

1. Glycolysis:
   • One molecule of glucose yields 2 ATP through substrate-level phosphorylation.
2. Krebs Cycle:
   • Each turn of the Krebs cycle produces 1 ATP (or GTP) through substrate-level phosphorylation.
   • Each glucose molecule results in two acetyl-CoA molecules, leading to two turns of the cycle.

3. Analysis and Detail

1. From Glycolysis:

   • ATP Yield: 2 ATP (from 1 glucose)

2. From Krebs Cycle:

   • ATP Yield per Turn: 1 ATP
   • Since glucose generates 2 acetyl-CoA, the cycle turns twice.
   • Total ATP from Krebs Cycle: $2 \text{ turns} \times 1 \text{ ATP/turn} = 2 \text{ ATP}$

4. Verify and Summarize

• Total ATP from Glycolysis: 2 ATP
• Total ATP from Krebs Cycle: 2 ATP
• Combined Total ATP from both processes when one glucose is consumed: $2 \text{ (from glycolysis)} + 2 \text{ (from Krebs cycle)} = 4 \text{ ATP}$

Final Answer

A total of 4 ATP molecules are formed during substrate-level phosphorylation when one glucose molecule is consumed.