Which two groups of the following formula are involved in peptide linkage between different amino acids?
`H_(2)N^(1)-underset(R^(4))underset(|)overset(H^(2))overset(|)( C)-COOH^(3)`

Options

A. 2 and 3
B. 1 and 3
C. 1 and 4
D. 2 and 4

Answer

To determine which two groups in the given amino acid structure are involved in peptide linkage, we need to analyze the structure and identify the relevant functional groups.

### Step-by-Step Solution:

1. **Identify the Structure of an Amino Acid**:
An amino acid generally consists of an amino group (-NH2), a carboxyl group (-COOH), and a variable side chain (R group). The general structure can be represented as:
\[ H_2N - C(R) - COOH \]
Here, R represents the side chain that varies among different amino acids.

2. **Recognize the Functional Groups**:
In the provided formula, we have:
- Group 1: Amino group (-NH2)
- Group 2: Alkyl group (R)
- Group 3: Carboxyl group (-COOH)
- Group 4: Hydrogen (H)

3. **Determine the Groups Involved in Peptide Bond Formation**:
A peptide bond is formed between the amino group of one amino acid and the carboxyl group of another amino acid. This process involves a dehydration synthesis reaction, where a water molecule is released.

4. **Identify the Relevant Groups**:
- The amino group (-NH2) from one amino acid (Group 1).
- The carboxyl group (-COOH) from another amino acid (Group 3).

5. **Conclusion**:
Therefore, the two groups involved in peptide linkage between different amino acids are:
- Group 1: Amino group (-NH2)
- Group 3: Carboxyl group (-COOH)

### Final Answer:
The two groups involved in peptide linkage between different amino acids are **Group 1 (Amino group -NH2)** and **Group 3 (Carboxyl group -COOH)**.

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