Open Question
Draw in the R-groups from memory for each of the charged amino acids at physiological pH.
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3. Amino Acids
Charged Amino Acids
Multiple Choice
In the context of charged amino acids, a basic amino acid has an R group that contains which of the following functional groups that can accept a proton and become positively charged at physiological pH?
A
A nonpolar hydrocarbon group composed only of carbon and hydrogen
B
An amino (nitrogen-containing) group, such as an amine/guanidinium/imidazole, that can be protonated
C
A carboxyl group that donates a proton to become negatively charged
D
A hydroxyl group that remains uncharged under most physiological conditions
Verified step by step guidance1
Understand that basic amino acids have side chains (R groups) that can accept protons (H+) and become positively charged at physiological pH (~7.4).
Recall the common functional groups in amino acid side chains: nonpolar hydrocarbon groups, amino groups, carboxyl groups, and hydroxyl groups.
Recognize that nonpolar hydrocarbon groups are composed only of carbon and hydrogen and do not accept protons, so they are not basic.
Identify that carboxyl groups tend to donate protons and become negatively charged, so they are acidic rather than basic.
Conclude that the functional groups capable of accepting protons and becoming positively charged at physiological pH are nitrogen-containing groups such as amino, guanidinium, or imidazole groups found in basic amino acids.
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