Membrane Proteins and Lipids

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What happens to the retinal molecule when it absorbs a photon?

It changes its conformation, resulting in a proton pumping action. (correct)

It breaks away from the surrounding protein.

It releases a proton from the extracellular side of the membrane.

It re-protonates itself to restore its original isomerized form.

What is the function of bacteriorhodopsin?

It pumps protons out of the cell.

It helps in the formation of a proton gradient. (correct)

It helps in the synthesis of ATP.

It facilitates the movement of ions across the cell membrane.

What is the characteristic of the interior of porins?

It is hydrophobic.

It is hydrophilic. (correct)

It is polar.

It is non-polar.

What is the typical structure of porins?

A barrel-like structure with 16-18 β sheets. Signup and view all the answers

Where are the residues more frequent in porins?

On the extracellular side. Signup and view all the answers

In which type of bacteria are porins found?

Gram-negative bacteria. Signup and view all the answers

What percentage of membrane proteins in red blood cells is comprised of Band 3?

25% Signup and view all the answers

What is the function of Band 3 in red blood cells?

Anion exchange Signup and view all the answers

What is the function of bacteriorhodopsin in Halobacterium halobium?

Using sunlight to pump protons out of the cell Signup and view all the answers

What is the structural feature of bacteriorhodopsin?

7 alpha helices crossing the membrane Signup and view all the answers

Which of the following is a characteristic of halophilic Archaebacteria?

Found in high-temperature brine/salt ponds Signup and view all the answers

What is the wavelength of light absorbed by bacteriorhodopsin?

570 nm Signup and view all the answers

What is the primary function of GPI-protein complexes in Protozoa?

Erythrocyte invasion Signup and view all the answers

What type of residues are rarely acetylated in GPI-protein complexes?

Glucosamine Signup and view all the answers

What is the purpose of a hydrophobicity analysis of a protein sequence?

To predict the presence of transmembrane helices Signup and view all the answers

In which organism is GPI-protein complex α-agglutinin involved in adhesion?

Fungi Signup and view all the answers

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 Signup and view all the answers

What is the function of the GPI-protein complex β1-3glucanase in plants?

Cell-wall biogenesis Signup and view all the answers

What percentage of proteins are found in chloroplast membranes?

70% Signup and view all the answers

What type of interactions anchor integral proteins to the membrane?

Hydrophobic interactions Signup and view all the answers

Which amino acids tend to be found at the lipid-water interface?

Trp, His, Tyr Signup and view all the answers

What is a typical feature of integral proteins?

20-25 aas folded into one or several α-helical domains Signup and view all the answers

What is the function of glycophorin A?

It is an example of an integral protein Signup and view all the answers

What is the function of maltoporin in E. coli?

To transport maltose into E. coli Signup and view all the answers

What is the function of lipid anchors in proteins?

To act as switches for protein affinity binding to the membranes Signup and view all the answers

What is the structure of Glycosyl phosphatidylinositol (GPI) anchors?

An oligosaccharide linked to inositol via an ethanolamine residue Signup and view all the answers

What is the function of GPI-anchored proteins?

To serve as hydrolytic enzymes, receptors, cell surface antigens or cell adhesion molecules Signup and view all the answers

What is the location of GPI-anchored proteins in the cell?

On the outer surface of the plasma membrane Signup and view all the answers

What is the type of linkage found in GPI anchors?

Amide, glycosidic, phosphodiester, and hydroxyester linkages Signup and view all the answers