Given a scientific question, generate a correct answer to it.

Let me give you an example: Who proposed the theory of evolution by natural selection?
The answer to this example can be: darwin
Here is why: This is a direct fact that Charles Darwin proposed the theory of evolution.

OK. solve this:
Integral proteins penetrate the hydrophobic interior of the what?
Answer:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
lipid bilayer