객관식
Which of the following functional groups on an amino acid side chain is polar and can become positively charged at physiological pH?
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3. Amino Acids
Amino Acid Groups
객관식
Which functional group on an amino acid is polar and can become positively charged at physiological pH?
A
Methyl group (–CH\(_3\))
B
Hydroxyl group (–OH)
C
Carboxyl group (–COOH)
D
Amino group (–NH\(_2\))
검증된 단계별 안내1
Step 1: Understand the concept of physiological pH, which is typically around 7.4, and how it affects the ionization of functional groups on amino acids.
Step 2: Recall that the amino group (–NH₂) is a polar functional group due to the electronegativity difference between nitrogen and hydrogen, making it capable of forming hydrogen bonds.
Step 3: At physiological pH, the amino group (–NH₂) can accept a proton (H⁺) and become positively charged, forming –NH₃⁺. This occurs because the pH is below the pKa of the amino group, which is typically around 9-10.
Step 4: Compare the other functional groups listed in the problem: The methyl group (–CH₃) is nonpolar and cannot become charged, the hydroxyl group (–OH) is polar but does not typically gain a positive charge at physiological pH, and the carboxyl group (–COOH) is polar but loses a proton to become negatively charged (–COO⁻) at physiological pH.
Step 5: Conclude that the amino group (–NH₂) is the correct answer because it is polar and can become positively charged at physiological pH, forming –NH₃⁺.
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