Amino acids are :

Options

A. acidic
B. basic
C. amphoteric
D. neutral

Answer

### Step-by-Step Solution:

1. **Definition of Amino Acids**:
Amino acids are organic compounds that serve as the building blocks of proteins. They contain both an amino group (-NH2) and a carboxyl group (-COOH), along with a side chain (R group) that varies between different amino acids.

2. **General Structure**:
The general formula for amino acids can be represented as:
\[ \text{R-CH(NH}_2\text{)-COOH} \]
Here, R represents the side chain that distinguishes one amino acid from another.

3. **Classification of Amino Acids**:
Amino acids can be classified based on their side chains (R groups) into different categories:
- **Non-polar (Hydrophobic)**: These amino acids have side chains that do not interact well with water. Examples include alanine, valine, and leucine.
- **Polar (Hydrophilic)**: These amino acids have side chains that can form hydrogen bonds with water. Examples include serine, threonine, and asparagine.
- **Charged (Acidic and Basic)**: Some amino acids have side chains that carry a charge. Acidic amino acids (like aspartic acid and glutamic acid) have a carboxyl group in their side chain, while basic amino acids (like lysine, arginine, and histidine) have an amino group in their side chain.

4. **Example of Amino Acids**:
- **Glycine (Gly)**: The simplest amino acid with the formula NH2-CH2-COOH. It does not have a chiral center.
- **Alanine (Ala)**: An amino acid with a methyl side chain (CH3).
- **Lysine (Lys)**: A basic amino acid with a side chain that contains an amino group.

5. **Properties of Amino Acids**:
- **Zwitterionic Nature**: In solution, amino acids can exist as zwitterions, where the amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-), resulting in a net charge of zero.
- **Chirality**: Most amino acids (except glycine) are chiral, meaning they can exist in two enantiomeric forms (D and L forms).