A basic amino acid is

Options

A. Leucine
B. Methionine
C. Aspartic acid
D. Lysine.

Answer

To determine which amino acid is classified as a basic amino acid, we can follow these steps:

### Step 1: Understand the Structure of Amino Acids
Amino acids have a general structure consisting of:
- A central carbon atom (C)
- An amino group (NH2)
- A carboxylic acid group (COOH)
- A variable side chain (R group) that determines the specific properties of each amino acid.

**Hint:** Remember that the R group is what differentiates one amino acid from another.

### Step 2: Classify Amino Acids
Amino acids can be classified based on the nature of their side chains:
- **Basic amino acids**: These have side chains that can accept protons (H+), making them basic in nature.
- **Acidic amino acids**: These have side chains that can donate protons, making them acidic.
- **Neutral amino acids**: These do not have a significant charge at physiological pH.

**Hint:** Focus on the properties of the R group to determine if the amino acid is basic, acidic, or neutral.

### Step 3: Identify Basic Amino Acids
The common basic amino acids include:
- **Lysine (Lys, K)**: Has an amino group in its side chain.
- **Arginine (Arg, R)**: Contains a guanidinium group, making it basic.
- **Histidine (His, H)**: Has an imidazole side chain that can be protonated.

**Hint:** Look for amino acids with additional amino groups in their side chains to identify basic amino acids.

### Step 4: Analyze the Given Options
From the question, we need to identify which of the provided options is a basic amino acid. The options given were:
1. Leucine (neutral)
2. Methionine (sulfur-containing)
3. Aspartic acid (acidic)
4. Lysine (basic)

**Hint:** Compare each option against the characteristics of basic amino acids.

### Step 5: Conclusion
Based on the analysis, **Lysine** is the correct answer as it is classified as a basic amino acid due to the presence of an additional amino group in its side chain.

**Final Answer:** The basic amino acid is **Lysine**.

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