Step 1: Understanding the Concept:
Amino acids have a basic structure consisting of a central alpha-carbon atom bonded to an amino group (\(\text{--NH}_2\)), a carboxyl group (\(\text{--COOH}\)), a hydrogen atom, and a variable side chain group (\(\text{R}\)).
The identity of the amino acid is determined by this variable \(\text{R}\) group.
Step 2: Key Formula or Approach:
Identify the \(\text{R}\) groups (side chains) for the given amino acids:
Leucine: \(\text{--CH}_2\text{--CH(CH}_3)_2\)
Alanine: \(\text{--CH}_3\)
Serine: \(\text{--CH}_2\text{OH}\)
Valine: \(\text{--CH(CH}_3)_2\)
Step 3: Detailed Explanation:
Alanine (Ala) is a simple non-polar amino acid.
Its structure is \(\text{H}_2\text{N--CH(CH}_3)\text{--COOH}\).
The side chain bonded to the alpha-carbon is just a methyl group (\(\text{--CH}_3\)).
Step 4: Final Answer:
Among the given options, Alanine is the amino acid that contains a methyl (\(\text{--CH}_3\)) group as its side chain.