Which of the following is CORRECT about amino acid ?

Options

A. It is a compound containing amino `(-NH_2)` and acidic group (–COOH)
B. It is a substituted methane.
C. Based on natural of 'R' group they are of many types
D. All of these

Answer

To solve the question regarding which statement is correct about amino acids, we can break down the information provided in the video transcript into a step-by-step analysis.

### Step-by-Step Solution:

1. **Understanding Amino Acids**:
- Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains two functional groups: an amino group (–NH2) and a carboxyl group (–COOH).
- **Hint**: Recall that amino acids are the fundamental units that make up proteins.

2. **Structure of Amino Acids**:
- The general structure of an amino acid includes a central carbon atom (alpha carbon) bonded to four groups: an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).
- **Hint**: Remember that the R group varies among different amino acids and determines their unique properties.

3. **Classification of Amino Acids**:
- Amino acids can be classified based on the nature of their R group. This classification includes categories such as nonpolar, polar, acidic, and basic amino acids.
- **Hint**: Think about how the R group influences the chemical behavior of the amino acid.

4. **Zwitterion Formation**:
- At physiological pH (around 7.4), amino acids exist predominantly in a zwitterionic form, where the amino group is protonated (–NH3+) and the carboxyl group is deprotonated (–COO–). This occurs within a pH range of approximately 2 to 9.
- **Hint**: Consider how the ionization states of the amino and carboxyl groups affect the overall charge of the amino acid.

5. **Conclusion**:
- Based on the above points, we can conclude that all the statements regarding amino acids mentioned in the question are correct. They contain amino and carboxyl groups, can be considered substituted methane, and vary based on their R groups.
- Therefore, the correct answer is "all of these."

### Final Answer:
**All of these statements are correct about amino acids.**