Bacteriorhodopsin pumps protons across the bacterial plasma membrane from the cytosolic side to the extracellular side of the membrane in a series of steps. Choose the step that correctly describe a step used to pump protons across the membrane. A. A proton is transferred from excited retinal to the Asp96 side chain. B. The chromaphore retinal absorbs a photon of light, causing a double bond in retinal to isomerize from trans to cis configuration. C. A proton from Asp96 on the cytosolic side of the protein is used to regenerate retinal. D. A proton from the cytosol side is transferred along multiple water molecules to Asp85.

Option B.

B. The chromaphore retinal absorbs a photon of light, causing a double bond in retinal to isomerize from trans to cis configuration.

Explanation:

Bacteriorhodopsin is a protein used by archaea or half bacteria that pumps proton across membrane by using the light energy from sun to move protons across membrane. It is found in purple membrane of archaea cells which is known as two dimensional crystalline patches.

It captures photon energy through chromophore retina which is covalently bound and transporting the photons against their electrochemical gradients from the cytoplasm to the extracellular space.

the median of the data is 4.5.