Question 1

A ligand-gated ion channel (such as the nicotinic acetylcholine receptor) is:

Accepted Answer

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. 
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. C

Question 2

Explain the differences between integral and peripheral membrane proteins.

Accepted Answer

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.

Question 3

Which process represents the HIGHEST energy state in membrane fusion?

Accepted Answer

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 
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 C

Question 4

Which statement does NOT describe a characteristic of valinomycin?

Accepted Answer

A)  This can act as an antibiotic. 
B)  This molecule is a small protein. 
C)  This compound preferentially transports potassium ions over sodium ions. 
D)  This compound has carbonyl groups that form coordination bonds to ions. 
A)  This can act as an antibiotic. 
B)  This molecule is a small protein. 
C)  This compound preferentially transports potassium ions over sodium ions. 
D)  This compound has carbonyl groups that form coordination bonds to ions.

Question 5

Which statement about the composition of biological membranes is FALSE?

Accepted Answer

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. 
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.

Question 6

Why are hydropathy plots NOT usually used to detect transmembrane $\beta$ strands in porins?

Accepted Answer

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. 
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.

Question 7

Which statement does NOT describe a process by which the specificity of aquaporins is ensured?

Accepted Answer

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+. 
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+.

Question 8

Which compound(s) is/are NOT enriched in lipid rafts?

Accepted Answer

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

Question 9

Which factor MOST significantly determines the direction in which an ion moves through an ion channel in a membrane?

Accepted Answer

A)  the electrochemical gradient across the membrane 
B)  the size and shape of the channel 
C)  the ion selectivity of the channel. 
D)  both the electrochemical gradient across the membrane and the size and shape of the channel 
E)  both the size and shape of the channel and the ion selectivity of the channel 
A)  the electrochemical gradient across the membrane 
B)  the size and shape of the channel 
C)  the ion selectivity of the channel. 
D)  both the electrochemical gradient across the membrane and the size and shape of the channel 
E)  both the size and shape of the channel and the ion selectivity of the channel

Question 10

Which statement about membranes is TRUE?

Accepted Answer

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. 
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.

Question 11

Which statement does NOT describe a characteristic of the fluid mosaic model of membranes?

Accepted Answer

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. 
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.

Question 12

In humans, the fatty acid composition of membrane lipids in skin cells is different from the fatty acid composition of membrane lipids in the internal organs because the internal organs function at a slightly higher temperature. Which difference in fatty acid composition is MOST likely to be observed?

Accepted Answer

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. 
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.

Question 13

Hydropathy analysis of the genomic sequence of the Type I membrane protein glycophorin A reveals two hydrophobic portions of the sequence that could correspond to transmembrane helices: one from residues 1-19 and one from residues 92-114. Only one of these helices is present in the mature proteins. Which one? What is the function of the other helix?

Accepted Answer

Glycophorin A is a well-characterized ty

Question 14

FRAP experiments are generally used in membrane studies to examine:

Accepted Answer

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. 
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.

Question 15

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why?
Histidine ($\mu$M)
Transport ($\mu$M/min)
2.5
42.5
7
119
16
240
31
490
72
1,000

Accepted Answer

Based on the provided data, it appears t

Question 16

As the temperature for a membrane lipid preparation is raised, what would be the order of states that would be adopted?

Accepted Answer

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 
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

Question 17

Facilitated diffusion through a biological membrane is:

Accepted Answer

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 
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

Question 18

Membrane lipids in tissue samples obtained from different parts of the leg of an arctic reindeer have different fatty acid compositions. Logically, what difference would you predict?

Accepted Answer

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. 
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.

Question 19

What kind of bond can link a myristoyl anchor to a polypeptide?

Accepted Answer

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 
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

Question 20

A process NOT involving the fusion of two membranes or two regions of the same membrane is:

Accepted Answer

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

Exam 11: Biological Membranes and Transport

A ligand-gated ion channel (such as the nicotinic acetylcholine receptor) is:

Explain the differences between integral and peripheral membrane proteins.

Which process represents the HIGHEST energy state in membrane fusion?

Which statement does NOT describe a characteristic of valinomycin?

Which statement about the composition of biological membranes is FALSE?

Why are hydropathy plots NOT usually used to detect transmembrane β\betaβ strands in porins?

Which statement does NOT describe a process by which the specificity of aquaporins is ensured?

Which compound(s) is/are NOT enriched in lipid rafts?

Which factor MOST significantly determines the direction in which an ion moves through an ion channel in a membrane?

Which statement about membranes is TRUE?

Which statement does NOT describe a characteristic of the fluid mosaic model of membranes?

FRAP experiments are generally used in membrane studies to examine:

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why? Histidine ( μ\muμ M) Transport ( μ\muμ M/min) 2.5 42.5 7 119 16 240 31 490 72 1,000

As the temperature for a membrane lipid preparation is raised, what would be the order of states that would be adopted?

Facilitated diffusion through a biological membrane is:

Membrane lipids in tissue samples obtained from different parts of the leg of an arctic reindeer have different fatty acid compositions. Logically, what difference would you predict?

What kind of bond can link a myristoyl anchor to a polypeptide?

A process NOT involving the fusion of two membranes or two regions of the same membrane is:

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

Why are hydropathy plots NOT usually used to detect transmembrane $\beta$ strands in porins?

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why? Histidine ( $\mu$ M) Transport ( $\mu$ M/min) 2.5 42.5 7 119 16 240 31 490 72 1,000