Identifying the R group of glutamic acid

Steps:

• Amino acids have a central alpha carbon bonded to an amino group (NH2), carboxyl group (COOH), hydrogen (H), and variable R group (side chain).
• Glutamic acid is an acidic amino acid with an additional carboxyl group in its side chain.
• The side chain for glutamic acid extends from the alpha carbon as -CH2-CH2-COOH.
• Match this structure to the choices, where D represents the full side chain.

Why D is correct:

• By definition in biochemistry, glutamic acid's R group is -CH2-CH2-COOH, providing its acidic properties.

Why the others are wrong:

• A: NH2 is the main amino group attached to the alpha carbon, not the side chain.
• B: H is the hydrogen atom on the alpha carbon, part of the core structure.
• C: COOH is the main carboxyl group of the amino acid backbone.

Final answer: D