This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Structure Function Relationships – Bacteriorhodopsin”.
1. Which of the following protein can capture light energy?
a) Glycophorin
b) GLUT 1
c) T cell receptor
d) Bacteriorhodopsin
View Answer
Explanation: Bacteriorhodopsin can capture light energy. It absorbs light energy and transforms it into chemical energy. Glycophorin, GLUT 1, and T cell receptorscannot capture light energy and convert it into chemical energy.
2. Bacteriorhodopsins contain which of the following pigments?
a) Chlorophyll
b) Phycobilins
c) Xanthophylls
d) Retinal
View Answer
Explanation: The pigment that bacteriorhodopsins contain is retinal. It is a green-light absorbing pigment and it is critical for the functioning of bacteriorhodopsins. Bacteriorhodopsins do not contain chlorophyll, phycobilins, and xanthophylls. Retinal is one of the several yellow or red carotenoid pigments.
3. The expression of bacteriorhodopsin is especially shown by which of the following organisms?
a) Mammals
b) Animals
c) Birds
d) Halobacteria
View Answer
Explanation: The expression of bacteriorhodopsin is especially shown by halobacteria. Halobacteria is a salt-loving bacterium. Mammals, animals, and birds do not show the expression of bacteriorhodopsin. Bacteriorhodopsin is used by archaea, mostly by halobacteria.
4. Bacteriorhodopsin acts as a proton pump.
a) False
b) True
View Answer
Explanation: The above statement is true. Bacteriorhodopsin acts as a proton pump. It captures light energy and uses it to move protons across the membrane out of the cell. The resulting proton gradient is subsequently converted into chemical energy.
5. How many transmembrane segments are present in the structure of bacteriorhodopsin?
a) Nine transmembrane helices
b) Eight transmembrane helices
c) Six transmembrane helices
d) Seven transmembrane helices
View Answer
Explanation: Bacteriorhodopsin contains seven transmembrane helices with short interconnecting loops. It is an integral membrane protein, with seven alpha-helices. These alpha helices are named A-G.
6. The interaction of retinal with the helix G is of which type?
a) Hydrophobic interaction
b) Non-covalent interaction
c) Hydrophobic interaction
d) Covalent interaction
View Answer
Explanation: The interaction of retinal with the helix G is of the Covalent type. The retinal molecule is covalently bound via a Schiff base to a conserved lysine residue on helix G. Retinal molecule is a critical pigment required for the functioning of bacteriorhodopsin.
7. Which of the following is true for bacteriorhodopsin?
a) It is an extrinsic protein
b) It is a lipid-anchored protein
c) It is a peripheral protein
d) It is an integral membrane protein
View Answer
Explanation: Bacteriorhodopsin is an integral membrane protein. It contains seven transmembrane helices. These helices are named helix A-G. The helices are used to span the lipid membrane. Apart from this, there is also a retinal molecule attached to one of the helices.
8. Which of the following conformation is showed by retinal before absorbing light?
a) Bent trans
b) Bent cis
c) Straight cis
d) Straight trans
View Answer
Explanation: The conformation showed by retinal before absorbing light is straight trans. Retinal is the main light-absorbing pigment present in bacteriorhodopsin. It converts light energy into a proton gradient, that is subsequently converted to chemical energy.
9. Which of the light powers the pumping of the protons across the membrane via bacteriorhodopsin?
a) Infrared light
b) Red light
c) Ultraviolet light
d) Greenlight
View Answer
Explanation: The green light powers the pumping of the protons across the membrane via bacteriorhodopsin. Bacteriorhodopsin is a molecular machine that pumps protons across the membrane to create a proton gradient.
10. Which of the following is true for the cytoplasm of Halobacteria?
a) It has fewer protons
b) It is neutral
c) It is highly acidic
d) It is highly alkaline
View Answer
Explanation: The cytoplasm of halobacteria is highly alkaline. The bacteriorhodopsin uses sunlight to pump protons outwards across their cell membrane, making inside 10,000-fold more alkaline, than the outside.
11. What is the absorption maximum of bacteriorhodopsin?
a) 448 nm
b) 706 nm
c) 346 nm
d) 568 nm
View Answer
Explanation: The absorption maximum of bacteriorhodopsin is 568 nm. The bacteriorhodopsin is purple in color and is most efficient at absorbing green light. Bacteriorhodopsin does not have an absorption maximum at 448 nm, 706 nm, and 346 nm.
12. The function of rhodopsin and bacteriorhodopsin is the same.
a) True
b) False
View Answer
Explanation: The function of rhodopsin and bacteriorhodopsin is not the same. Both rhodopsin and bacteriorhodopsin belong to the 7TM receptor family of proteins, but rhodopsin is a G-protein coupled receptor, and bacteriorhodopsin is not. Thus, they have different functions.
13. Which of the following bacterium is prominently known to contain bacteriorhodopsin?
a) Aspergillus niger
b) Entamoeba histolytica
c) Escherichia coli
d) Halobacterium salinarum
View Answer
Explanation: Halobacterium salinarum is the bacterium that is prominently known to contain bacteriorhodopsin. It is a halophilic archaebacterium. It is a salt-loving bacterium and it grows best in 4.3 M NaCl.
14. Which of the following conformation is showed by retinal after absorbing light?
a) Bent trans
b) Straight cis
c) Straight trans
d) Bent cis
View Answer
Explanation: The conformation showed by retinal after absorbing light is bent cis. While the conformation shown by retinal before absorbing light is straight trans. This conformational change results in the harvesting of light energy.
15. After photoisomerization of the retinal molecule, which amino acid residue becomes a proton acceptor of the donor proton from the retinal molecule?
a) Met69
b) Ala93
c) Lys216
d) Asp85
View Answer
Explanation: After photoisomerization of the retinal molecule, Asp85 amino acid residue becomes a proton acceptor of the donor proton from the retinal molecule. Reprotonation of the retinal molecule by Asp96 restores its original isomerized form.
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