Exam 11: Biological Membranes and Transport

A) liquid-ordered, gel phase, liquid-disordered
B) liquid-disordered, liquid-ordered, gel phase
C) liquid-disordered, gel phase, liquid-ordered
D) gel phase, liquid-disordered, liquid-ordered
E) gel phase, liquid-ordered, liquid-disordered

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A) endocytosis.
B) entry of enveloped viruses into cells.
C) entry of glucose into cells.
D) exocytosis.
E) reproductive budding in yeast.

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Glycophorin A is a well-characterized ty...

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A) The length of a transmembrane $\beta$ strand is typically shorter than that of an $\beta$ helix.
B) Amino acids in transmembrane $\beta$ strands in porins may not be exclusively hydrophobic.
C) Amino acid side chains project away from the polypeptide in a $\beta$ sheet
D) Answers A and B are both correct.
E) All of the answers are correct.

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A) Hydrophobic interactions predominate between lipids in the membrane.
B) Proteins and lipids are able to move laterally at different rates.
C) Protein structures are able to move from one leaflet to another.
D) Noncovalent forces predominate in intermolecular interactions.

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Integral membrane proteins are embedded within the lipid bilayer of the cell membrane, while peripheral membrane proteins are only temporarily associated with the membrane. Integral membrane proteins have hydrophobic regions that allow them to interact with the hydrophobic tails of the phospholipid molecules in the membrane, making them firmly embedded within the membrane structure. In contrast, peripheral membrane proteins are typically attached to the membrane through electrostatic interactions or binding to integral membrane proteins, and can be easily removed from the membrane without disrupting its structure. Integral membrane proteins often have important functions related to cell signaling, transport of molecules across the membrane, and cell adhesion. They are typically more difficult to isolate from the membrane due to their strong association with the lipid bilayer. Peripheral membrane proteins, on the other hand, are involved in processes such as cell signaling, cytoskeletal organization, and membrane trafficking. They can be easily isolated from the membrane through mild treatments that disrupt the electrostatic or protein-protein interactions holding them in place. Overall, the main difference between integral and peripheral membrane proteins lies in their association with the lipid bilayer of the cell membrane and their respective functions within the cell.

A) The channel contains a negatively charged Asp residue to scavenge protons and H₃O⁺.
B) The diameter of the channel narrows to 2.8 Å.
C) There are carbonyl backbone residues in the channel that hydrogen bond with water.
D) Arg and His residues in the channel repel protons and H₃O⁺.
E) Electric dipoles of short $\alpha$ helices repel protons and H₃O⁺.

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A) sphingolipids
B) cholesterol
C) GPI-linked proteins
D) farnesylated proteins
E) All of these molecules are enriched in lipid rafts.

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Based on the provided data, it appears t...

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A) transverse diffusion rates.
B) active transport rates.
C) lateral diffusion rates.
D) both transverse diffusion rates and active transport rates.
E) both transverse diffusion rates and lateral diffusion rates.

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A) an ester bond to an internal serine
B) an amide bond to a glycine
C) a thioester to a cysteine
D) an ester bond to the C-terminus
E) a thioether bond to a cysteine side chain

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A) Membrane lipids from tissue near the hooves (feet) contain a greater proportion of unsaturated fatty acids relative to that in the upper leg.
B) Membrane lipids from tissue in the upper leg contain a greater proportion of unsaturated fatty acids relative to that in the hooves (feet) .
C) Both answers A and B are equally likely.
D) Neither answer A nor B is likely.

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A) a charged lipid in the membrane bilayer that allows ions to pass through.
B) a membrane protein that permits a ligand to pass through the membrane only when opened by the appropriate ion.
C) a membrane protein that permits an ion to pass through the membrane only when opened by the appropriate ligand.
D) a molecule that binds to the membrane thereby allowing ions to pass through.
E) always requires a second ligand to close the channel once it is opened.

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C

A) driven by a difference of solute concentration.
B) driven by ATP.
C) endergonic.
D) generally irreversible.
E) not specific with respect to the substrate

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A) Most plasma membranes contain more than 70% proteins.
B) Sterol lipids are common in bacterial plasma membranes.
C) Sterol lipids are common in human cell plasma membranes.
D) Sterol lipids are common in plant cell plasma membranes.
E) The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.

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A) Skin cells show lower levels of 18:0 relative to 18:1 AND higher levels of 16:0 relative to 18:0.
B) Skin cells show higher levels of 20:0 relative to 18:0 AND higher levels of 18:2 relative to 18:0.
C) Skin cells show lower levels of 20:0 relative to 18:0 AND lower levels of 18:0 relative to 18:2.
D) Skin cells show higher levels of 18:2 relative to 18:0 AND lower levels of 16:0 relative to 18:0.
E) Both answers A and C are true.

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A) In a given eukaryotic cell type (e.g., a hepatocyte) , all intracellular membranes have essentially the same complement of lipids and proteins.
B) The carbohydrate found in membranes is virtually all part of either glycolipids or glycoproteins.
C) The plasma membranes of the cells of vertebrate animals contain more cholesterol than the mitochondrial membranes.
D) The ratio of lipid to protein varies widely among cell types in a single organism.
E) Triacylglycerols are not commonly found in membranes.

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A) formation of coiled-coils in SNARE proteins
B) formation of the fusion pore
C) the hemifusion state
D) the expansion of the fusion pore
E) lipid mixing in both outer and inner leaflets

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C