Which of the following statements regarding cofactors of enzymes is correct?

Options

A. Zinc is a cofactor for the proteolytic enzyme carboxypeptidase.
B. Nicotinamide adenine dinucleotide contain the vitamine riboflavin
C. Cofactor is the part of enzyme which does not affect the catalytic activity of the enzyme
D. Prosthetic groups are distinguished from other cofactors in that prosthetic groups are loosely bound to the apoenzyme

Answer

To determine which statement regarding cofactors of enzymes is correct, we will analyze each statement provided in the video transcript step by step.

### Step 1: Analyze the first statement
**Statement:** Zinc is a co-factor for the proteolytic enzyme carboxypeptidase.

**Analysis:** This statement is correct. Zinc acts as a co-factor for carboxypeptidase, which is an enzyme that requires this metal ion to function properly. Carboxypeptidase is indeed a holoenzyme, meaning it is an active enzyme that contains its co-factor.

### Step 2: Analyze the second statement
**Statement:** Nicotinamide adenine dinucleotide (NAD) contains the vitamin riboflavin.

**Analysis:** This statement is incorrect. NAD is derived from nicotinic acid (vitamin B3) and not riboflavin (vitamin B2). Therefore, this statement does not hold true.

### Step 3: Analyze the third statement
**Statement:** A co-factor is a part of an enzyme that does not affect the catalytic activity of the enzyme.

**Analysis:** This statement is also incorrect. Cofactors play a crucial role in the catalytic activity of enzymes. They assist in the catalysis process, and without them, the enzyme may not function effectively.

### Step 4: Analyze the fourth statement
**Statement:** Prosthetic groups are loosely bound to apoenzymes.

**Analysis:** This statement is incorrect. Prosthetic groups are tightly bound to the apoenzyme (the inactive form of the enzyme without its co-factor). They are not loosely bound; rather, they are integral to the enzyme's structure and function.

### Conclusion
After analyzing all the statements, the only correct statement is the first one: **Zinc is a co-factor for the proteolytic enzyme carboxypeptidase.**

### Final Answer
The correct statement regarding cofactors of enzymes is: **Zinc is a co-factor for the proteolytic enzyme carboxypeptidase.**

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