The amino acid in which R group` CH_2CH_2COOH` is
(a) aspartic acid
(b) glutamic acid
(c) valine
(d) threonine

Options

A. aspartic acid
B. glutamic acid
C. valine
D. threonine

Answer

To solve the question regarding the amino acid with the R group `CH2CH2COOH`, we will analyze the options given and identify the correct amino acid based on the structure of the R group.

### Step-by-Step Solution:

1. **Understanding the Structure of Amino Acids**:
- Amino acids have a general structure consisting of an amino group (-NH2), a carboxylic group (-COOH), a hydrogen atom (H), and an R group (side chain) that varies among different amino acids.

2. **Analyzing the Given R Group**:
- The R group provided in the question is `CH2CH2COOH`. This indicates that the side chain consists of two carbon atoms followed by a carboxylic acid group.

3. **Reviewing the Options**:
- (a) Aspartic acid: The R group is `CH2COOH`. This does not match `CH2CH2COOH`.
- (b) Glutamic acid: The R group is `CH2CH2COOH`. This matches the given R group.
- (c) Valine: The R group is `CH(CH3)2`, which does not match.
- (d) Threonine: The R group is `CH(OH)CH3`, which also does not match.

4. **Identifying the Correct Answer**:
- Since the R group `CH2CH2COOH` corresponds to glutamic acid, we can conclude that the correct answer is option (b) glutamic acid.

### Final Answer:
(b) glutamic acid