Question 1

The specificity of aquaporins for water is not ensured by which of the following?

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+. A

Question 2

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 3

If the hydrophobic interior of a membrane were about 3 nm thick,what would be the minimum number of amino acids in a stretch of transmembrane $\alpha$ helix?

Accepted Answer

The dimensions of an $\alpha$helix are about 5.4 Å/turn,and there are 3.6 residues/turn,so each residue extends the helix by about 1.5 Å or 0.15 nm.To span 3 nm of lipid bilayer will therefore require a minimum of 20 residues.

Question 4

Glycosphingolipids and cholesterol cluster together in membrane regions known as "__________." These microdomains are more __________ than the surrounding phospholipid-rich membrane due to a high content of __________ fatty acids.These regions are rich in proteins that are anchored to the membrane by covalently attached __________ and __________ groups and also those anchored by GPI linkage.Proteins aggregated in this fashion are often functionally related.Examples are (1)__________ proteins and (2)__________ proteins.

Accepted Answer

"rafts";ordered;satu

Question 5

An integral membrane protein can be extracted with:

Accepted Answer

A) a buffer of alkaline or acid pH. 
B) a chelating agent that removes divalent cations. 
C) a solution containing detergent. 
D) a solution of high ionic strength. 
E) hot water. 
A) a buffer of alkaline or acid pH. 
B) a chelating agent that removes divalent cations. 
C) a solution containing detergent. 
D) a solution of high ionic strength. 
E) hot water.

Question 6

Which of these is a general feature of the lipid bilayer in all biological membranes?

Accepted Answer

A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer. 
B) Individual lipid molecules in one face (monolayer)of the bilayer readily diffuse (flip-flop)to the other monolayer. 
C) Polar,but uncharged,compounds readily diffuse across the bilayer. 
D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules. 
E) The polar head groups face inward toward the inside of the bilayer. 
A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer. 
B) Individual lipid molecules in one face (monolayer)of the bilayer readily diffuse (flip-flop)to the other monolayer. 
C) Polar,but uncharged,compounds readily diffuse across the bilayer. 
D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules. 
E) The polar head groups face inward toward the inside of the bilayer.

Question 7

What is an amphipathic compound? Explain how such compounds contribute to the structure of biological membranes.

Accepted Answer

An amphipathic compound has one region o

Question 8

Consider the transport of K+ from the blood (where its concentration is about 4 mM)into an erythrocyte that contains 150 mM K+.The transmembrane potential is about 60 mV,inside negative relative to outside.The free-energy change for this transport process is: (These values may be of use to you: R = 8.315 J/mol.K;T = 298 K;9 (Faraday constant)= 96,480 J/V;N = 6.022 *1023/mol. )

Accepted Answer

A) about 5 J/mol. 
B) about 15 J/mol. 
C) about 5 kJ/mol. 
D) about 15 kJ/mol. 
E) impossible to calculate with the information given. 
A) about 5 J/mol. 
B) about 15 J/mol. 
C) about 5 kJ/mol. 
D) about 15 kJ/mol. 
E) impossible to calculate with the information given.

Question 9

What are three differences between ion channels and ion transporters?

Accepted Answer

(1)The rate of ion movement through chan

Question 10

What are the principle features of the fluid mosaic model of membranes?

Accepted Answer

The principle features of the fluid mosa

Question 11

ABC transporters are not known to facilitate the following process:

Accepted Answer

A) moving cancer drugs out of cancer cells. 
B) moving antibiotics out of bacteria. 
C) moving membrane lipids from the inner leaflet to the outer leaflet. 
D) moving chloride ions in the lung. 
E) moving vitamin E into lipocytes. 
A) moving cancer drugs out of cancer cells. 
B) moving antibiotics out of bacteria. 
C) moving membrane lipids from the inner leaflet to the outer leaflet. 
D) moving chloride ions in the lung. 
E) moving vitamin E into lipocytes.

Question 12

Which of these statements 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 13

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by:

Accepted Answer

A) a decrease in temperature. 
B) an increase in fatty acyl chain length. 
C) an increase in the number of double bonds in fatty acids. 
D) an increase in the percentage of phosphatidyl ethanolamine 
E) the binding of water to the fatty acyl side chains. 
A) a decrease in temperature. 
B) an increase in fatty acyl chain length. 
C) an increase in the number of double bonds in fatty acids. 
D) an increase in the percentage of phosphatidyl ethanolamine 
E) the binding of water to the fatty acyl side chains.

Question 14

A plant breeder has developed a new frost-resistant variety of tomato that contains higher levels of unsaturated fatty acids in membrane lipids than those found in standard tomato varieties.However,when temperatures climb above 95 °F,this frost-resistant variety dies,whereas the standard variety continues to grow.Provide a likely explanation of the biochemical basis of increased tolerance to cold and increased susceptibility to heat of this new tomato variety.

Accepted Answer

More unsaturated fatty acids will cause

Question 15

Distinguish between simple diffusion (SD),facilitated diffusion (FD),and active transport (AT)across a membrane for the following questions.(More than one may be true. )
(a)Which processes are energy dependent?
(b)Which processes need some kind of carrier protein(s)?
(c)Which processes can be saturated by substrate?
(d)Which processes can establish a concentration gradient?
(e)How much energy does it take to transport an uncharged substrate in,if its starting inside concentration is 10-fold greater than outside?

Accepted Answer

(a)AT only
(b)FD and

Question 16

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?

Accepted Answer

At first glance,the mechanism appears to

Question 17

A protein is found to extend all the way through the membrane of a cell.Describe this protein in terms of the location of particular types of amino acid side chains in its structure and its ability to move within the membrane.

Accepted Answer

This integral membrane protein associate

Question 18

The bacterium E.coli can grow at 20 °C or at 40 °C.At which growth temperature would you expect the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids,and why?

Accepted Answer

At 40 °C,the membranes of E.coli will co

Question 19

Which of the following are not enzymes involved in moving phospholipids from one leaflet to another?

Accepted Answer

A) Flippases that move phosphatidylethanolamine and phosphatidylserine 
B) Floppases that move phospholipids from the cytosolic leaflet to the extracellular leaflet 
C) Flip-floppases that allow phospholipids to move back and forth between the inner and outer leaflets 
D) Scramblases that allow phospholipids to move down their concentration gradient 
E) Phosphatidylinositol transfer proteins that play a role in lipid signaling 
A) Flippases that move phosphatidylethanolamine and phosphatidylserine 
B) Floppases that move phospholipids from the cytosolic leaflet to the extracellular leaflet 
C) Flip-floppases that allow phospholipids to move back and forth between the inner and outer leaflets 
D) Scramblases that allow phospholipids to move down their concentration gradient 
E) Phosphatidylinositol transfer proteins that play a role in lipid signaling

Question 20

A hydropathy plot is used to:

Accepted Answer

A) determine the water-solubility of a protein. 
B) deduce the quaternary structure of a membrane protein. 
C) determine the water content of a native protein. 
D) extrapolate for the true molecular weight of a membrane protein. 
E) predict whether a given protein sequence contains membrane-spanning segments. 
A) determine the water-solubility of a protein. 
B) deduce the quaternary structure of a membrane protein. 
C) determine the water content of a native protein. 
D) extrapolate for the true molecular weight of a membrane protein. 
E) predict whether a given protein sequence contains membrane-spanning segments.

Exam 11: Biological Membranes and Transport

The specificity of aquaporins for water is not ensured by which of the following?

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

If the hydrophobic interior of a membrane were about 3 nm thick,what would be the minimum number of amino acids in a stretch of transmembrane α\alphaα helix?

An integral membrane protein can be extracted with:

Which of these is a general feature of the lipid bilayer in all biological membranes?

What is an amphipathic compound? Explain how such compounds contribute to the structure of biological membranes.

What are three differences between ion channels and ion transporters?

What are the principle features of the fluid mosaic model of membranes?

ABC transporters are not known to facilitate the following process:

Which of these statements about the composition of biological membranes is false?

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by:

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?

A protein is found to extend all the way through the membrane of a cell.Describe this protein in terms of the location of particular types of amino acid side chains in its structure and its ability to move within the membrane.

The bacterium E.coli can grow at 20 °C or at 40 °C.At which growth temperature would you expect the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids,and why?

Which of the following are not enzymes involved in moving phospholipids from one leaflet to another?

A hydropathy plot is used to:

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

Recombinant Dna Technology

Lipids

Biosignaling

Principles of Bioenergetics

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

Integration and Hormonal Regulation of Mammalian Metabolism

Genes and Chromosomes

Dna Metabolism

Rna Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

If the hydrophobic interior of a membrane were about 3 nm thick,what would be the minimum number of amino acids in a stretch of transmembrane $\alpha$ helix?