Which of the following gropus is present invariably at the two terminals of protein ?

Options

A. Methyl and ethyl
B. Aldehyde and ketone
C. Amino and carboxylic
D. Acid and alcohol

Answer

To answer the question "Which of the following groups is present invariably at the two terminals of protein?", we need to understand the structure of proteins and their building blocks, which are amino acids.

### Step-by-Step Solution:

1. **Understanding Proteins**:
- Proteins are macromolecules made up of smaller units called amino acids.

2. **Structure of Amino Acids**:
- Each amino acid consists of a central carbon atom (alpha carbon) attached to four different groups:
- An amino group (-NH2)
- A carboxyl group (-COOH)
- A hydrogen atom (-H)
- A variable side chain (R group) that differs among different amino acids.

3. **Peptide Bond Formation**:
- When amino acids link together through peptide bonds, they form a polypeptide chain, which eventually folds into a functional protein.

4. **Terminal Groups of Proteins**:
- Since proteins are formed from amino acids, they will have two distinct ends:
- The N-terminus (amino terminal) where the amino group is located.
- The C-terminus (carboxyl terminal) where the carboxyl group is located.

5. **Conclusion**:
- Therefore, the two groups that are invariably present at the terminals of a protein are the amino group at one end and the carboxyl group at the other end.

### Final Answer:
The groups present invariably at the two terminals of a protein are the **amino group and the carboxyl group**.

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