Amino acids are substituted______

Answer

To solve the question "Amino acids are substituted ______," we need to identify what amino acids can be referred to as substituted.

1. **Understanding Amino Acids**: Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains an amino group (-NH2), a carboxyl group (-COOH), and a side chain (R group) that varies among different amino acids.

2. **Substituted Methane**: The term "substituted methane" refers to a methane molecule (CH4) where one or more hydrogen atoms are replaced by other atoms or groups. In the context of amino acids, the hydrogen atom in methane can be replaced by different functional groups, including amino groups or side chains.

3. **Example of Substituted Methane**: Lysine is an example of an amino acid that can be classified as a substituted methane. In lysine, one of the hydrogen atoms in the methane structure is replaced by an amino group and additional carbon chains, which gives it its unique properties.

4. **Conclusion**: Based on the above understanding, we can fill in the blank in the question. Amino acids can be referred to as "substituted methane" because they can be derived from methane by substituting one or more hydrogen atoms with different functional groups.

**Final Answer**: Amino acids are substituted **methane**.

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