Question

On the plasma membrane of the archaeon Halobacterium salinarum, bacteriorhodopsin is found in high density in patches of purple membrane. Which statement best describes this protein?

1) It is a light-gated anion channel
2) It is a single-pass transmembrane protein
3) It uses the energy stored in the protein gradient to transport small molecules
4) It changes conformation in response to light

Answer 1

Bacteriorhodopsin in Halobacterium salinarum changes conformation in response to light and uses light energy to create a proton gradient across the plasma membrane, allowing ATP synthesis.

Step-by-step explanation:

Bacteriorhodopsin is a protein found in the plasma membranes of the archaea Halobacterium salinarum. This protein is involved in the process of photosynthesis, where it harnesses light energy to pump protons across the membrane, creating an electrochemical gradient. The energy stored in this gradient is then used for the synthesis of ATP. Bacteriorhodopsin undergoes a conformational change when it absorbs light, which allows it to acquire protons on the inside of the cell and release them on the outside, thereby contributing to the proton gradient required for energy production. The correct description of this protein among the options given in the question is that it changes conformation in response to light (Option 4).

Other notable proteins such as halorhodopsin also use light energy but for different purposes like pumping chloride ions into the cell to prevent water loss. Halobacterium salinarum can give high-salt environments a distinctive reddish or purple color due to the presence of bacteriorhodopsin, which is structurally similar to the rhodopsin found in human eyes, and used for vision.