Which of these amino acid R groups would likely be found in the hydrophobic pocket?

Which of these amino acid structures is reasonable/accurate at a given pH (i.e. makes sense in low pH or high pH)

Question

Which of these amino acid R groups would likely be found in the hydrophobic pocket?

Which of these amino acid structures is reasonable/accurate at a given pH (i.e. makes sense in low pH or high pH)

BlackTom AI · Accepted Answer

Branched aliphatic side chains are nonpolar and pack into hydrophobic pockets, so A and B are the ones that belong there. A and B show alkyl, branched R groups (isopropyl/sec‑butyl–type groups like valine/leucine/isoleucine) which lack polar atoms and are hydrophobic. C, by contrast, shows polar/unsaturated functionality (a double bond conjugated to a carbonyl and nearby lone pairs/heteroatoms) that will be more polar or ionizable and therefore not favored in a hydrophobic pocket.

Relevant knowledge points and concepts
- Hydrophobic side chains: alkyl and aromatic R groups (e.g., Val, Leu, Ile, Phe) pack into hydrophobic pockets. They lack charged or strongly polar functional groups.
- Protonation states of the backbone (and ionizable side chains) depend on pH: at low pH carboxyl groups are protonated (COOH) and amines are protonated (NH3+); at high pH carboxylates are deprotonated (COO−) and amines can be neutral (NH2). Any drawn structure must reflect a realistic protonation state for some pH.

Step-by-step reasoning
1. Inspect R groups: A and B are purely hydrocarbon, branched chains with no heteroatoms — textbook hydrophobic R groups. Therefore they are the ones that would be found in a hydrophobic pocket.
2. Examine C: contains polar/ionizable features (double bond adjacent to carbonyl, lone pairs on oxygen, or an OH), making it polar/ionizable and not appropriate for a hydrophobic pocket.
3. For “reasonable/accurate at a given pH”: realistic amino acid drawings must show protonation consistent with some pH. The depictions for A and B (neutral hydrocarbon side chains) are pH‑independent and therefore reasonable at any pH. C’s drawn combination of charges/tautomers (as sketched) is not a realistic stable protonation state for an amino acid at a single pH (it implies contradictory/unstable protonation/tautomeric form).

Why the correct answer is correct
- A and B are nonpolar, branched alkyl R groups (thus hydrophobic) and their structures as drawn are chemically sensible across pH ranges. C is polar/ionizable and/or drawn in an unrealistic protonation/tautomeric form, so it is neither hydrophobic nor clearly a valid single‑pH depiction.

Why other options are incorrect (brief)
- Any option claiming “all” includes C as hydrophobic or valid — incorrect because C is polar/ionizable or drawn inconsistently. Options that single out only C (or “none, C”) contradict the clear nonpolar nature of A and B.

Conclusion
Therefore the correct choice is A, B — A and B are the hydrophobic R groups and the depicted structures for them are reasonable — which matches the provided answer.

Which of these amino acid R groups would likely be found in the hydrophobic pocket? Which of these amino acid structures is reasonable/accurate at a given pH (i.e. makes sense in low pH or high pH)单项选择题

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