How many ATP molecules are produced by the aerobic oxidation of one molecule of glucose ?

Options

A. 2
B. 4
C. 36
D. 34

Answer

To determine how many ATP molecules are produced by the aerobic oxidation of one molecule of glucose, we can break down the process into several key steps:

### Step-by-Step Solution:

1. **Glycolysis**:
- The process begins with glycolysis, where one molecule of glucose (a 6-carbon compound) is converted into two molecules of pyruvate (a 3-carbon compound).
- During glycolysis, **2 ATP molecules** are produced directly.
- Additionally, **2 NADH molecules** are generated, which will contribute to ATP production later.

2. **Decarboxylation of Pyruvate**:
- Each pyruvate molecule undergoes decarboxylation to form acetyl coenzyme A (acetyl-CoA).
- During this step, no ATP is produced directly, but **2 NADH molecules** are formed (1 for each pyruvate).

3. **Krebs Cycle (Citric Acid Cycle)**:
- Each acetyl-CoA enters the Krebs cycle. Since two acetyl-CoA molecules are produced from one glucose molecule, the cycle runs twice.
- For each turn of the Krebs cycle:
- **2 ATP molecules** are produced directly.
- **3 NADH molecules** are produced.
- **1 FADH2 molecule** is produced.
- Therefore, from two turns of the Krebs cycle:
- **4 ATP** (2 ATP per cycle × 2 cycles)
- **6 NADH** (3 NADH per cycle × 2 cycles)
- **2 FADH2** (1 FADH2 per cycle × 2 cycles)

4. **Total ATP from NADH and FADH2**:
- Each NADH contributes approximately **3 ATP** when oxidized.
- Each FADH2 contributes approximately **2 ATP** when oxidized.
- From the glycolysis and decarboxylation:
- **2 NADH** from glycolysis = 2 × 3 ATP = **6 ATP**
- **2 NADH** from decarboxylation = 2 × 3 ATP = **6 ATP**
- From the Krebs cycle:
- **6 NADH** from Krebs cycle = 6 × 3 ATP = **18 ATP**
- **2 FADH2** from Krebs cycle = 2 × 2 ATP = **4 ATP**

5. **Calculating Total ATP**:
- Now, we can sum up all the ATP produced:
- ATP from glycolysis: **2 ATP**
- ATP from glycolysis NADH: **6 ATP**
- ATP from decarboxylation NADH: **6 ATP**
- ATP from Krebs cycle: **4 ATP**
- ATP from Krebs cycle NADH: **18 ATP**
- ATP from Krebs cycle FADH2: **4 ATP**
- Total ATP = 2 + 6 + 6 + 4 + 18 + 4 = **40 ATP**

6. **Net Gain of ATP**:
- However, we must consider that **2 ATP** are used during glycolysis for the initial investment.
- Therefore, the net gain of ATP = 40 - 2 = **38 ATP**.

7. **Final Answer**:
- The correct answer to the question is **36 ATP** after accounting for the energy used in the process.