Question 1

Explain why ATP-powered proton pumps cannot by themselves acidify the lumen of the lysosome.

Accepted Answer

The V-class proton pump responsible for acidifying the lumen of the lysosome,where the net movement of electric charge occurs during transport,is electrogenic.As each proton is pumped into the lumen,it leaves behind a negatively charged ion in the cytosol.Positive and negative ions attract each other across the membrane of the lysosome,which causes an electric potential.Soon,pumping leads to a buildup of protons in the lumen,which repels other protons.At this point,a significant transmembrane proton concentration gradient cannot be established.Thus,to generate an acidic environment necessary to breakdown components imported into the lysosome,proton transport must be accompanied by an equal number of anions,in this case in the form of Cl-,into the lumen.

Question 2

Both ethanol and glycine are small molecules of approximately equal molecular weight.However,the membrane is much more permeable to ethanol than glycine.What accounts for the large difference in membrane permeability between ethanol and glycine?

Accepted Answer

Ethanol is a small alcohol;glycine is a small amino acid.Glycine,like all amino acids,is a zwitterion.At neutral pH,the amino group of glycine is positively charged and the carboxyl group is negatively charged.Charged groups are impermeable to lipid bilayers.

Question 3

The ΔG calculation for the two-Na⁺/one-glucose symporter includes which of the following terms?

Accepted Answer

A) RT ln [glucoseᵢn]/[glucoseₒᵤt] 
B) 2RT ln [Na⁺ᵢn]/[Na⁺ₒᵤt] 
C) 2FE 
D) all of the above 
A) RT ln [glucoseᵢn]/[glucoseₒᵤt] 
B) 2RT ln [Na⁺ᵢn]/[Na⁺ₒᵤt] 
C) 2FE 
D) all of the above D

Question 4

Which statement describes the mode of action of the ABCB1 transporter (the first eukaryotic ABC transporter to be recognized)?

Accepted Answer

A) During transport,the ligand binding site is alternately exposed to the exoplasmic and the cytoplasmic side of the membrane. 
B) During transport,a conserved aspartate residue is phosphorylated. 
C) This class of pumps transports only H⁺ ions. 
D) This transporter acts as a chloride channel. 
A) During transport,the ligand binding site is alternately exposed to the exoplasmic and the cytoplasmic side of the membrane. 
B) During transport,a conserved aspartate residue is phosphorylated. 
C) This class of pumps transports only H⁺ ions. 
D) This transporter acts as a chloride channel.

Question 5

Describe the patch-clamping technique.Why do investigators often use frog oocytes in their patch-clamping investigations?

Accepted Answer

By pressing a special electrode against

Question 6

Ion channels achieve selectivity in transport through all of the following mechanisms EXCEPT:

Accepted Answer

A) evolution from distinct and different parent proteins. 
B) divergent evolution from a single type of channel protein. 
C) low activation energy for selective passage of the dehydrated ion. 
D) use of P segments to form an ion selectivity filter. 
A) evolution from distinct and different parent proteins. 
B) divergent evolution from a single type of channel protein. 
C) low activation energy for selective passage of the dehydrated ion. 
D) use of P segments to form an ion selectivity filter.

Question 7

Propose a rationale for why the import of amino acids or sugars into cells is typically coupled to Na⁺ ion import.

Accepted Answer

The Na⁺/K⁺ ATPase establishes and mainta

Question 8

Aquaporins are:

Accepted Answer

A) β-barrel proteins in the outer membrane of bacteria. 
B) ABC proteins. 
C) symporters. 
D) water channels. 
A) β-barrel proteins in the outer membrane of bacteria. 
B) ABC proteins. 
C) symporters. 
D) water channels.

Question 9

The major ATP-powered pump responsible for maintaining ion gradients across the plasma membrane of mammalian cells is:

Accepted Answer

A) the calmodulin-activated plasma membrane Ca²⁺ ATPase. 
B) the sarcoplasmic reticulum Ca²⁺ ATPase. 
C) the vacuolar F-class proton pump. 
D) the plasma-membrane Na⁺/K⁺ ATPase. 
A) the calmodulin-activated plasma membrane Ca²⁺ ATPase. 
B) the sarcoplasmic reticulum Ca²⁺ ATPase. 
C) the vacuolar F-class proton pump. 
D) the plasma-membrane Na⁺/K⁺ ATPase.

Question 10

Describe how aquaporins facilitate the movement of water across the plasma membrane.

Accepted Answer

Aquaporins are water-channel proteins th

Question 11

Which of the following is true about cystic fibrosis?

Accepted Answer

A) The normal CFTR channel protein is a chloride uniporter,but CF patients have a mutation that makes it require ATP. 
B) CFTR mutations result in a mutated protein,which pumps too many chloride ions out of the cell. 
C) There are no treatments for patients with CF that are specifically targeted to the CFTR receptor. 
D) Patients with the most common mutation make a CFTR protein that is not present in the membrane. 
A) The normal CFTR channel protein is a chloride uniporter,but CF patients have a mutation that makes it require ATP. 
B) CFTR mutations result in a mutated protein,which pumps too many chloride ions out of the cell. 
C) There are no treatments for patients with CF that are specifically targeted to the CFTR receptor. 
D) Patients with the most common mutation make a CFTR protein that is not present in the membrane.

Question 12

In which of the following cases is energy NOT needed for transmembrane transport?

Accepted Answer

A) Lysine moves into the cell against its concentration gradient via the Na⁺/lysine symporter. 
B) Potassium ions (K⁺)move out of the cell down the K⁺ concentration gradient via potassium channels. 
C) Glucose moves into the cell down its concentration gradient via a glucose uniporter. 
D) The second and third answers are correct. 
E) all of the above 
A) Lysine moves into the cell against its concentration gradient via the Na⁺/lysine symporter. 
B) Potassium ions (K⁺)move out of the cell down the K⁺ concentration gradient via potassium channels. 
C) Glucose moves into the cell down its concentration gradient via a glucose uniporter. 
D) The second and third answers are correct. 
E) all of the above

Question 13

Why are nongated channels important in the generation of a negative electric potential (voltage)of 50-70 mV inside the cell with respect to the outside?

Accepted Answer

If there is no ion movement across the m

Question 14

The magnitude of the membrane electrical potential is calculated by:

Accepted Answer

A) the Nernst equation. 
B) the Michaelis-Menten equation. 
C) the Faraday equation. 
D) the Bose-Einstein equation. 
A) the Nernst equation. 
B) the Michaelis-Menten equation. 
C) the Faraday equation. 
D) the Bose-Einstein equation.

Question 15

The H⁺/K⁺ ATPase on the apical surface of parietal cells exports H⁺ and imports K⁺.How is the buildup of excess K⁺ ions in the parietal cell cytosol prevented?

Accepted Answer

A K⁺ channel on the apical sur

Question 16

Which of the following is true about glucose transporters?

Accepted Answer

A) GLUT-2 and GLUT-4 are expressed on all cell types. 
B) All the members of the GLUT family have the same affinity for glucose. 
C) Cells that express GLUT-1 and GLUT-3 display more glucose uptake than cells expressing GLUT-2 at physiological blood concentrations (5 mM). 
D) GLUT proteins are specific for glucose molecules and will not transport other sugars. 
A) GLUT-2 and GLUT-4 are expressed on all cell types. 
B) All the members of the GLUT family have the same affinity for glucose. 
C) Cells that express GLUT-1 and GLUT-3 display more glucose uptake than cells expressing GLUT-2 at physiological blood concentrations (5 mM). 
D) GLUT proteins are specific for glucose molecules and will not transport other sugars.

Question 17

The glucose uniporter GLUT1 has a Km of 1.5 mM for d-glucose and 30 mM for d-galactose.At a concentration of 5 mM for each,what is the rate of glucose transport relative to galactose transport? The Vmₐₓ may be assumed to be the same for both.

Accepted Answer

A) 3.7-fold slower 
B) equal 
C) 5.5-fold faster 
D) 20-fold faster 
A) 3.7-fold slower 
B) equal 
C) 5.5-fold faster 
D) 20-fold faster

Question 18

Calculate the ΔG for the movement of Na⁺ from inside a typical mammalian cell to outside.

Accepted Answer

the cellular concentration of Na⁺ is 12

Question 19

Amino acid entry into cells can occur via uniporters or symporters.If the rate of leucine entry into the cell increases when the pH decreases,this suggests:

Accepted Answer

A) leucine is being transported by a uniporter. 
B) leucine is being actively pumped across the membrane against its concentration gradient. 
C) leucine is being transported by a H⁺ symporter. 
D) leucine is crossing the membrane via simple diffusion. 
A) leucine is being transported by a uniporter. 
B) leucine is being actively pumped across the membrane against its concentration gradient. 
C) leucine is being transported by a H⁺ symporter. 
D) leucine is crossing the membrane via simple diffusion.

Question 20

The osmotic potential of a hypotonic solution should cause an animal cell to _____,but with frog oocytes prevent this effect by _____.

Accepted Answer

A) burst;not expressing aquaporins 
B) shrink;not expressing aquaporins 
C) burst;expressing more aquaporins 
D) shrink;expressing more aquaporins 
A) burst;not expressing aquaporins 
B) shrink;not expressing aquaporins 
C) burst;expressing more aquaporins 
D) shrink;expressing more aquaporins

Exam 10: Transmembrane Transport of Ions and Small Molecules

Explain why ATP-powered proton pumps cannot by themselves acidify the lumen of the lysosome.

Both ethanol and glycine are small molecules of approximately equal molecular weight.However,the membrane is much more permeable to ethanol than glycine.What accounts for the large difference in membrane permeability between ethanol and glycine?

The ΔG calculation for the two-Na⁺/one-glucose symporter includes which of the following terms?

Which statement describes the mode of action of the ABCB1 transporter (the first eukaryotic ABC transporter to be recognized)?

Describe the patch-clamping technique.Why do investigators often use frog oocytes in their patch-clamping investigations?

Ion channels achieve selectivity in transport through all of the following mechanisms EXCEPT:

Propose a rationale for why the import of amino acids or sugars into cells is typically coupled to Na⁺ ion import.

Aquaporins are:

The major ATP-powered pump responsible for maintaining ion gradients across the plasma membrane of mammalian cells is:

Describe how aquaporins facilitate the movement of water across the plasma membrane.

Which of the following is true about cystic fibrosis?

In which of the following cases is energy NOT needed for transmembrane transport?

Why are nongated channels important in the generation of a negative electric potential (voltage)of 50-70 mV inside the cell with respect to the outside?

The magnitude of the membrane electrical potential is calculated by:

The H⁺/K⁺ ATPase on the apical surface of parietal cells exports H⁺ and imports K⁺.How is the buildup of excess K⁺ ions in the parietal cell cytosol prevented?

Which of the following is true about glucose transporters?

The glucose uniporter GLUT1 has a Km of 1.5 mM for d-glucose and 30 mM for d-galactose.At a concentration of 5 mM for each,what is the rate of glucose transport relative to galactose transport? The Vmₐₓ may be assumed to be the same for both.

Calculate the ΔG for the movement of Na⁺ from inside a typical mammalian cell to outside.

Amino acid entry into cells can occur via uniporters or symporters.If the rate of leucine entry into the cell increases when the pH decreases,this suggests:

The osmotic potential of a hypotonic solution should cause an animal cell to _____,but with frog oocytes prevent this effect by _____.

Chemical Foundations

Molecular Genetic Techniques

Protein Structure and Function

Culturing and Visualizing Cells

Fundamental Molecular Genetic Mechanisms

Bio-membrane Structure

Genes Genomics and Chromosomes

Transcriptional Control of Gene Expression

Post-Transcriptional Gene Control

Cellular Energetics

Moving Proteins Into Membranes and Organelles

Vesicular Traffic, Secretion, and Endocytosis

Signal Transduction and G-Protein Coupled Receptors

Signaling Pathways That Control Gene Activity

Cell Organization and Movement I: Microfilaments

Cell Organization and Movement II: Microtubules and Intermediate Filaments

Regulating the Eukaryotic Cell Cycle

Integrating Cells Into Tissues

Cell Birth, Lineage, and Death

Nerve Cells

Immunology

Cancer

Filters

The osmotic potential of a hypotonic solution should cause an animal cell to _,but with frog oocytes prevent this effect by _.