Bacteriorhodopsin genes found in some extremely halophilic (salt-loving) Euryarc

Question

Bacteriorhodopsin genes found in some extremely halophilic (salt-loving) Euryarchaeota code for light-driven proton pumps. Use of metagenomic analyses of ocean samples has indicated presence of genes for similar proteins in a variety of marine Bacteria as well as in the genomes of the novel group of Euryarcheota described in the chapter opener. Where in a bacterial or archaeal cell would you expect these proteins to be localized? Choose the best answer.

a. nucleus

b. flagellin

c. cytoplasmic

d. membrane cytoplasm

Hint 1. Function of bacteriorhodopsin A variety of genes for rhodopsin-like proteins have been identified in metagenomic analyses of water from surface oceanic environments. These genes are similar to the genes for bacteriorhodopsin found in some halophilic (salt-loving) members of the domain Archaea. The proteins produced are associated with energy conservation using development of a proton gradient in the presence of light.

Hint 2. What is a proton pump? A proton pump is a type of protein that actively transports protons.

Explanation / Answer

Bacteriorhodopsin is a transmembrane protein (integral protein) with seven helices passing through the membrane. It is used to pump proton across the membrane and thus creating gradient of protein between cytoplams and extracellular space. This gradient of proton is used for synthesizing ATP. These proteins are densely located in portion of membrane known as purple membrane. Hence correct anaswer is membrane cytoplasm (option D).

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