Which three structural groups are present in all standard amino acids?

• A. Carboxyl group (\(-COOH\)), phosphate group (\(-PO_4^{3-}\)), and side chain (R group)
• B. Amino group (\(-NH_2\)), carboxyl group (\(-COOH\)), and hydrogen atom
• C. Amino group (\(-NH_2\)), hydroxyl group (\(-OH\)), and side chain (R group)
• D. Amino group (\(-NH_2\)), methyl group (\(-CH_3\)), and carboxyl group (\(-COOH\))

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by understanding the structure of standard amino acids. Amino acids are the building blocks of proteins and share a common structure consisting of specific functional groups.
2. Step 2: Identify the three structural groups that are present in all standard amino acids. These include: (1) an amino group (\(-NH_2\)), (2) a carboxyl group (\(-COOH\)), and (3) a hydrogen atom attached to the central carbon.
3. Step 3: Note that the central carbon atom, known as the alpha carbon, is also bonded to a variable side chain (R group), which differentiates one amino acid from another. However, the R group is not one of the three universal structural groups.
4. Step 4: Eliminate incorrect options by analyzing the functional groups listed. For example, phosphate groups (\(-PO_4^{3-}\)), hydroxyl groups (\(-OH\)), and methyl groups (\(-CH_3\)) are not universally present in all amino acids.
5. Step 5: Confirm that the correct answer is the combination of amino group (\(-NH_2\)), carboxyl group (\(-COOH\)), and hydrogen atom, as these are the consistent structural groups found in all standard amino acids.