Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. Which of the following are acidic?

Options

A. `(CH_(3))_(2)CH-underset(" "NH_(2))underset(|)(CH)-COOH`
B. `HOOC-CH_(2)-CH_(2)-underset(" "NH_(2))underset(|)(CH)-COOH`
C. `H_(2)N-CH_(2)-CH_(2)-CH_(2)-COOH`
D. `HOOC-CH_(2)-underset(" "NH_(2))underset(|)(CH)-COOH`

Explanation

To determine which amino acids are classified as acidic, we need to analyze the number of carboxyl groups (–COOH) and amino groups (–NH2) present in each option. Acidic amino acids have more carboxyl groups than amino groups.

Let's break down the options step by step:

### Step 1: Analyze the first option
- Structure: CH2-CH3-CH-COOH (with NH2 group)
- Count:
- Carboxyl groups (–COOH): 1
- Amino groups (–NH2): 1
- Conclusion: The number of carboxyl groups is equal to the number of amino groups. Therefore, this amino acid is **neutral**.

### Step 2: Analyze the second option
- Structure: H2N-CH2-CH2-CH-COOH (with another COOH)
- Count:
- Carboxyl groups (–COOH): 2
- Amino groups (–NH2): 1
- Conclusion: There are more carboxyl groups than amino groups. Therefore, this amino acid is **acidic**.

### Step 3: Analyze the third option
- Structure: H2N-CH2-CH-COOH (with NH2 group)
- Count:
- Carboxyl groups (–COOH): 1
- Amino groups (–NH2): 1
- Conclusion: The number of carboxyl groups is equal to the number of amino groups. Therefore, this amino acid is **neutral**.

### Step 4: Analyze the fourth option
- Structure: COOH-CH2-CH-COOH (with NH2 group)
- Count:
- Carboxyl groups (–COOH): 2
- Amino groups (–NH2): 1
- Conclusion: There are more carboxyl groups than amino groups. Therefore, this amino acid is **acidic**.

### Final Conclusion
The acidic amino acids from the options given are:
- **Second option** (H2N-CH2-CH2-CH-COOH with two carboxyl groups)
- **Fourth option** (COOH-CH2-CH-COOH with two carboxyl groups)

### Summary of Acidic Amino Acids:
- **Acidic Amino Acids**: Second and Fourth options
- **Neutral Amino Acids**: First and Third options