Question

multiple choice question
select the statement that is true of transmembrane domains.

• transmembrane domains are composed of hydrophobic amino acids.
• transmembrane domains are attached to the surface of the membrane.
• transmembrane domains are composed of hydrophilic amino acids.

Explanation:

1. Analyze the first option: Cell membranes have a hydrophobic interior (lipid tails). Transmembrane domains (parts of integral membrane proteins) span the membrane, so they interact with the hydrophobic lipid tails. Hydrophobic amino acids can interact favorably with the hydrophobic membrane interior, so transmembrane domains are often composed of hydrophobic amino acids.
2. Analyze the second option: Transmembrane domains span the membrane, not just attach to the surface. Peripheral membrane proteins attach to the surface, while transmembrane domains (of integral proteins) go through the membrane. So this statement is false.
3. Analyze the third option: Hydrophilic amino acids would be repelled by the hydrophobic membrane interior. Since transmembrane domains are within the membrane, they can't be composed of hydrophilic amino acids (they would not be stable in the hydrophobic environment of the membrane's interior). So this statement is false.

Answer:

A. Transmembrane domains are composed of hydrophobic amino acids.