Final answer:
Sequence b) IMIVLMLLPLA is the most likely to form a single transmembrane domain due to its high content of hydrophobic amino acids and absence of charged or highly polar residues, in alignment with the characteristic features of transmembrane helices.
Step-by-step explanation:
The student's question involves determining which amino acid sequence represents a helix that forms a single transmembrane domain. Given that hydrophobic alpha-helical domains are characteristic of membrane-spanning proteins, a sequence that is predominantly hydrophobic is more likely to form a transmembrane domain. The helical regions interact with the hydrophobic interior of the lipid bilayer, which is why transmembrane domains contain a high proportion of hydrophobic amino acids.
Let's evaluate the given sequences:
- a) VGHSLSIFTLV - This sequence contains both hydrophobic (V, G, I, F, T, L) and hydrophilic (H, S) residues, but might not be enough to span a membrane.
- b) IMIVLMLLPLA - This sequence is rich in hydrophobic residues (I, M, V, L, P, A) and absent of charged or polar residues, suggesting it's likely to form a single transmembrane domain.
- c) ILHFFHQYMM - This sequence also contains hydrophobic residues but includes multiple polar/charged ones (H, Q, Y) which do not favor membrane spanning.
- d) VTLHKNMFLT - Although this sequence has several hydrophobic residues, the presence of K (lysine) significantly increases its hydrophilicity.
Considering the hydrophobicity of the amino acids, sequence b) IMIVLMLLPLA is the most likely candidate for forming a single transmembrane domain due to its high content of hydrophobic residues and absence of charged or highly polar amino acids. This aligns with our understanding that transmembrane regions are predominantly hydrophobic to interact with the lipid bilayer's hydrophobic core.