How many ATPs are formed per glucose molecule in Krebs cycle ?

Options

A. 2
B. 24
C. 6
D. 28

Answer

To determine how many ATPs are formed per glucose molecule in the Krebs cycle, we can follow these steps:

### Step 1: Understand the Krebs Cycle
The Krebs cycle, also known as the citric acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. It occurs in the mitochondria and processes acetyl-CoA derived from carbohydrates, fats, and proteins.

### Step 2: Identify ATP Production
During one turn of the Krebs cycle, 2 molecules of ATP are produced directly. This is a crucial point because it indicates the immediate yield of ATP from the cycle itself.

### Step 3: Consider NADH and FADH2 Production
In addition to ATP, the Krebs cycle produces electron carriers:
- 6 molecules of NADH
- 2 molecules of FADH2

### Step 4: Calculate ATP from NADH
Each NADH molecule can generate approximately 3 ATP when it is oxidized in the electron transport chain. Therefore, for 6 NADH:
\[ 6 \, \text{NADH} \times 3 \, \text{ATP/NADH} = 18 \, \text{ATP} \]

### Step 5: Calculate ATP from FADH2
Each FADH2 molecule can generate approximately 2 ATP when oxidized. Therefore, for 2 FADH2:
\[ 2 \, \text{FADH2} \times 2 \, \text{ATP/FADH2} = 4 \, \text{ATP} \]

### Step 6: Sum All ATP Production
Now, we can sum the ATP produced directly in the Krebs cycle and the ATP generated from NADH and FADH2:
\[ \text{Total ATP} = \text{ATP from Krebs cycle} + \text{ATP from NADH} + \text{ATP from FADH2} \]
\[ \text{Total ATP} = 2 + 18 + 4 = 24 \, \text{ATP} \]

### Final Answer
Thus, the total number of ATP molecules formed per glucose molecule in the Krebs cycle is **24 ATP**.

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