At how many steps substrate level phoshorplation occurs during glycolysis:

Options

A. One
B. Two
C. Three
D. Four

Answer

To determine how many steps substrate-level phosphorylation occurs during glycolysis, we can follow these steps:

### Step 1: Understand Glycolysis
Glycolysis is a metabolic pathway that breaks down glucose (a 6-carbon molecule) into pyruvate (a 3-carbon molecule). This process occurs in the cytoplasm and does not require oxygen, making it anaerobic.

**Hint:** Remember that glycolysis involves the breakdown of glucose into pyruvate.

### Step 2: Identify the Steps in Glycolysis
Glycolysis consists of 10 enzymatic steps. Each step involves different transformations of the glucose molecule, leading to the production of energy carriers and pyruvate.

**Hint:** Familiarize yourself with the 10 steps of glycolysis and the main transformations that occur.

### Step 3: Define Substrate-Level Phosphorylation
Substrate-level phosphorylation is a process where ATP is produced directly from ADP and a phosphate group during a specific enzymatic reaction, without the involvement of an electron transport chain.

**Hint:** Focus on the definition of substrate-level phosphorylation and how it differs from oxidative phosphorylation.

### Step 4: Identify Steps with Substrate-Level Phosphorylation
In glycolysis, substrate-level phosphorylation occurs in two specific steps:
1. **Step 7:** Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, where ATP is generated.
2. **Step 10:** Conversion of phosphoenolpyruvate to pyruvate, where another ATP is generated.

**Hint:** Look for the steps in glycolysis where ATP is produced directly from ADP.

### Step 5: Count the Steps
From the identified steps, we see that substrate-level phosphorylation occurs in two steps of glycolysis.

**Hint:** Keep track of the steps where ATP is produced directly to arrive at the final count.

### Conclusion
Thus, substrate-level phosphorylation occurs in **2 steps** during glycolysis.

**Final Answer:** The answer is **2** (Option B).