Which of the following functional groups confers acidic properties to amino acids?

• A. Hydroxyl group (\(-OH\))
• B. Carboxyl group (\(-COOH\))
• C. Sulfhydryl group (\(-SH\))
• D. Amino group (\(-NH_2\))

Answer: (B)

Verified step by step guidance

1. Understand the concept of acidic properties: Acidic properties in molecules are typically conferred by functional groups that can donate a proton (\(\text{H}\)^+) to the surrounding environment, lowering the pH.
2. Examine the carboxyl group (\(\text{-COOH}\)): The carboxyl group contains a hydroxyl group (\(\text{-OH}\)) attached to a carbon atom that is also double-bonded to an oxygen atom. This group can ionize by losing a proton (\(\text{H}\)^+), forming a negatively charged carboxylate ion (\(\text{-COO}\)^-). This ability to donate a proton makes it acidic.
3. Compare the hydroxyl group (\(\text{-OH}\)): While the hydroxyl group is polar and can form hydrogen bonds, it does not readily donate a proton under physiological conditions, so it does not confer significant acidic properties.
4. Analyze the sulfhydryl group (\(\text{-SH}\)): The sulfhydryl group is involved in forming disulfide bonds and is not strongly acidic under physiological conditions. It does not readily donate a proton like the carboxyl group.
5. Evaluate the amino group (\(\text{-NH}\)_2): The amino group is basic rather than acidic. It tends to accept a proton (\(\text{H}\)^+) rather than donate one, which is the opposite of what is required for acidic properties.