Which functional group(s) are present in all standard amino acids?

Step 3: Analyze the options provided in the problem. Hydroxyl ( $\left(\mathrm{-OH}\right)$) and methyl ( $\left(\mathrm{-CH}{3}_{}\right)$) groups are not present in all amino acids, as these are specific to certain R groups. Similarly, sulfhydryl ( $\left(\mathrm{-SH}\right)$) and phosphate ( $\left(\mathrm{-PO}{4}^{\mathrm{3-}}\right)$) groups are not universally present in amino acids.

Step 4: Confirm that the amino group ( $\left(\mathrm{-NH}{2}_{}\right)$) and carboxyl group ( $\left(\mathrm{-COOH}\right)$) are the functional groups present in all standard amino acids. These groups are essential for the formation of peptide bonds during protein synthesis.