`alpha`- Amino acids are the building blocks of proteins. About 20 `alpha`-amino acids have been isolated by the hydrolysis of proteins. All these amino acids except glycine are chiral and have L-configuration. Ten amino acids (valine , leucine, isoleucine , phenylalanine, methionine , trytophan , threonine , lysine , arginine and histidine) which the body cannot synthesize are called essential amino acids. The remaining ten are called non -essential amino acids. All `alpha`-amino acids exist are zwitterions each of which has a specific isoelectric point. Above isoelectric point , a `alpha`-amino acid exists as an anion. Two, three or many `alpha`-amino acids join together to form di-,tri -or polypeptides or proteins respectively. Each polypeptides or protein has a free amino group at one end called the N-terminal end and a free carboxyl group at the other end called the C-terimal end. Sanger's reagent (i.e., 2,4-dinitrofluorobenzene) is used to determine the N-terminal end while C-terimal end is determined by hydrazinolysis.
Which of the following reagents is used to determine the C-terminal end in a polypeptide ?

Options

A. Hydrazine
B. 2,4-Dintrophenylhydrazine
C. 2,4-Dinitrofluorobenzene
D. 3,5-Difluorenitrobenzene

Answer

To determine the C-terminal end of a polypeptide, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structure of Polypeptides**:
- Polypeptides are chains of amino acids linked by peptide bonds. Each polypeptide has an N-terminal end (free amino group) and a C-terminal end (free carboxyl group).

2. **Identifying the Reagents**:
- The question asks for the reagent used to determine the C-terminal end of a polypeptide.

3. **Hydrazinolysis**:
- According to the information provided, the C-terminal end can be determined by a process called hydrazinolysis. This involves the use of hydrazine (N2H4) as a reagent.

4. **Conclusion**:
- Therefore, the reagent used to determine the C-terminal end of a polypeptide is **hydrazine**.

### Final Answer:
The reagent used to determine the C-terminal end in a polypeptide is **hydrazine**.

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