Use the following information when answering the corresponding question(s).
Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A). Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane. There are two classes of rhodopsins. According to Oded Beje, one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection. The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis: pumping of protons or chloride ions across cell membranes. Oded Beje was the first, in September 2000, to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria. [SOURCE: O. Beje et al., Science 289 (2000): 1902.]
-For a protein to be an integral membrane protein, it would have to be ________.
A) hydrophilic
B) hydrophobic
C) amphipathic, with at least one hydrophobic region
D) completely covered with phospholipids
E) exposed on only one surface of the membrane

Question

Quizplus · Accepted Answer

An integral membrane protein must have at least one hydrophobic region in order to be embedded within the hydrophobic interior of the plasma membrane. However, it must also have hydrophilic regions in order to interact with the aqueous environment on either side of the membrane, making it amphipathic. Option A is incorrect because hydrophilic proteins would not be able to embed in the hydrophobic membrane. Option B is partially correct but does not account for the need for hydrophilic regions. Option D is incorrect because phospholipids are not typically involved in directly covering proteins. Option E is incorrect because integral membrane proteins are embedded within the membrane and not exposed on only one surface.

Use the Following Information When Answering the Corresponding Question(s)