Final answer:
The transmembrane portion of membrane proteins would be unlikely to be composed of an alpha-helix made of hydrophilic amino acids. These domains are typically hydrophobic and non-polar.
Step-by-step explanation:
The transmembrane portion of membrane proteins shown in the figure would be unlikely to be composed of an alpha-helix made of hydrophilic amino acids because the transmembrane domains of proteins are typically hydrophobic and non-polar.
This is because the hydrophobic interior of the lipid bilayer repels hydrophilic amino acids, making it energetically unfavorable for them to be located in the transmembrane region. Instead, hydrophilic amino acids tend to be found on the surface of the protein, interacting with the aqueous environment inside or outside the cell.
For example, the hydrophobic transmembrane alpha helix of glycophorin A, a membrane protein in red blood cells, is composed of hydrophobic amino acids that anchor the protein within the lipid bilayer.