Which molecule links glycolysis with fermentation as well as TCA cycle

Options

A. Ethanol
B. Acetaldehyde
C. PEP
D. Pyruvic acid.

Answer

To solve the question "Which molecule links glycolysis with fermentation as well as TCA cycle?", we can follow these steps:

### Step 1: Understand the process of glycolysis
Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP and NADH in the process. This occurs in the cytoplasm of the cell.

**Hint:** Remember that glycolysis is the first step in both aerobic and anaerobic respiration.

### Step 2: Identify the products of glycolysis
The end product of glycolysis is pyruvate (or pyruvic acid). This molecule is crucial as it can enter different metabolic pathways depending on the availability of oxygen.

**Hint:** Focus on the end product of glycolysis and its fate in different conditions.

### Step 3: Determine the fate of pyruvate in aerobic respiration
In the presence of oxygen, pyruvate is converted into acetyl-CoA through a process known as the link reaction. Acetyl-CoA then enters the TCA cycle (Krebs cycle) for further energy production.

**Hint:** Think about what happens to pyruvate when oxygen is available.

### Step 4: Determine the fate of pyruvate in anaerobic respiration
In the absence of oxygen, pyruvate undergoes fermentation. This can lead to the production of lactic acid (in lactic acid fermentation) or ethanol and carbon dioxide (in alcoholic fermentation).

**Hint:** Consider what pyruvate becomes when oxygen is not present.

### Step 5: Conclude which molecule links glycolysis with both fermentation and the TCA cycle
Since pyruvate is the product of glycolysis and serves as a precursor for both aerobic respiration (linking to the TCA cycle) and anaerobic respiration (linking to fermentation), it is the molecule that connects these pathways.

**Final Answer:** The molecule that links glycolysis with fermentation as well as the TCA cycle is **pyruvate**.