Precursor of niacin is

Options

A. lysine
B. theronine
C. tryptophan
D. glycoine

Answer

To determine the precursor of niacin, we need to analyze the options provided: lysine, threonine, tryptophan, and glycine.

1. **Understanding Niacin**: Niacin, also known as nicotinic acid, is a form of vitamin B3. It is an essential nutrient for humans and plays a crucial role in various metabolic processes.

2. **Identifying Precursors**: A precursor is a substance from which another substance is formed. In this case, we are looking for the amino acid that can be converted into niacin.

3. **Reviewing Amino Acids**:
- **Lysine**: This amino acid is essential but does not directly convert to niacin.
- **Threonine**: Another essential amino acid, but it is not a direct precursor for niacin.
- **Tryptophan**: This is an essential amino acid that can be converted into niacin in the body.
- **Glycine**: This is a non-essential amino acid and does not serve as a precursor for niacin.

4. **Conclusion**: Among the given options, tryptophan is the only amino acid that serves as a precursor for niacin. The body can synthesize niacin from tryptophan, making it the correct answer.

Thus, the precursor of niacin is **tryptophan**.