29 Questions
What happens to the retinal molecule when it absorbs a photon?
It changes its conformation, resulting in a proton pumping action.
What is the function of bacteriorhodopsin?
It helps in the formation of a proton gradient.
What is the characteristic of the interior of porins?
It is hydrophilic.
What is the typical structure of porins?
A barrel-like structure with 16-18 β sheets.
Where are the residues more frequent in porins?
On the extracellular side.
In which type of bacteria are porins found?
Gram-negative bacteria.
What percentage of membrane proteins in red blood cells is comprised of Band 3?
25%
What is the function of Band 3 in red blood cells?
Anion exchange
What is the function of bacteriorhodopsin in Halobacterium halobium?
Using sunlight to pump protons out of the cell
What is the structural feature of bacteriorhodopsin?
7 alpha helices crossing the membrane
Which of the following is a characteristic of halophilic Archaebacteria?
Found in high-temperature brine/salt ponds
What is the wavelength of light absorbed by bacteriorhodopsin?
570 nm
What is the primary function of GPI-protein complexes in Protozoa?
Erythrocyte invasion
What type of residues are rarely acetylated in GPI-protein complexes?
Glucosamine
What is the purpose of a hydrophobicity analysis of a protein sequence?
To predict the presence of transmembrane helices
In which organism is GPI-protein complex α-agglutinin involved in adhesion?
Fungi
What type of side chains can be attached to the ethanolamine, inositol, and mannose residues in GPI-protein complexes?
Ethanolamine phosphate, mannose, galactose, and sialic acid
What is the function of the GPI-protein complex β1-3glucanase in plants?
Cell-wall biogenesis
What percentage of proteins are found in chloroplast membranes?
70%
What type of interactions anchor integral proteins to the membrane?
Hydrophobic interactions
Which amino acids tend to be found at the lipid-water interface?
Trp, His, Tyr
What is a typical feature of integral proteins?
20-25 aas folded into one or several α-helical domains
What is the function of glycophorin A?
It is an example of an integral protein
What is the function of maltoporin in E. coli?
To transport maltose into E. coli
What is the function of lipid anchors in proteins?
To act as switches for protein affinity binding to the membranes
What is the structure of Glycosyl phosphatidylinositol (GPI) anchors?
An oligosaccharide linked to inositol via an ethanolamine residue
What is the function of GPI-anchored proteins?
To serve as hydrolytic enzymes, receptors, cell surface antigens or cell adhesion molecules
What is the location of GPI-anchored proteins in the cell?
On the outer surface of the plasma membrane
What is the type of linkage found in GPI anchors?
Amide, glycosidic, phosphodiester, and hydroxyester linkages
This quiz covers the structure and function of membrane proteins, including their composition and characteristics. It also touches on the differences between integral and peripheral proteins. Test your knowledge of membrane biology!
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