Question 1

Digoxin is a member of the cardiac glycoside family of drugs. This drug can be used to treat patients with atrial fibrillation since it slows heart rate. Cardiac glycosides function by inhibiting which class of membrane transporter?
A) antiporters
B) facilitative diffusers
C) symporters
D) uniporters

Accepted Answer

Cardiac glycosides like digoxin inhibit the Na+/K+ ATPase pump, which is a type of antiporter. This inhibition leads to an increase in intracellular calcium, which enhances cardiac contractility and slows heart rate.  The cardiac glycosides function by inhibiting the action of Na+/K+-ATPases. These transporters transport Na+ into the cell while simultaneously transporting K+ out. Thus, they function as classical antiporters.

Question 2

Aquaporins are a class of transporters that are involved in the transport of water across membranes. The aquaporins belong to which type of transporter family?
A) active
B) b-barrel channels (porins)
C) a-channels
D) facilitated
E) passive

Accepted Answer

The aquaporin proteins are made up of 6 transmembrane a-helices arranged in a right-handed bundle. The a-type channels are homo- or hetero-oligomeric structures that in the latter case consist of several different proteins. The a-type class of channel protein has between 2 and 22 transmembrane a-helical domains, thus the derivation of the name of this type of channel.

Question 3

You are treating a patient who complains of having an intense or uncontrollable thirst with a strong craving for ice water. The patient produces large amounts of urine (8-10 L per day). Additional symptoms include fatigue, headache, irritability, and muscle pains. Given the symptoms you suspect nephrogenic diabetes insipidus. If this diagnosis is correct, which of the following membrane transporter types would be defective in your patient? A) aquaporin B) F-type ATPase C) Na⁺ / K⁺ -ATPase D) P-type ATPase E) SLC40A1 (ferroportin)

Accepted Answer

Nephrogenic diabetes insipidus is characterized by the kidney's inability to respond to antidiuretic hormone (ADH), often due to defects in aquaporin channels, which are responsible for water reabsorption in the kidney.

Question 4

A patient who presents with unique facial features, recurrent infections, persistent leukocytosis, defective neutrophil chemotaxis, and severe growth and mental retardation would likely be manifesting these symptoms due to a deficiency in which of the following transport proteins? A) aquaporin B) F-type ATPase C) GDP-fucose transporter (FUCT1, SLC35C1) D) Na⁺ / K⁺ -ATPase E) P-type ATPase

Accepted Answer

The symptoms described are characteristic of Leukocyte Adhesion Deficiency Type II (LAD II), which is caused by a defect in the GDP-fucose transporter (FUCT1, SLC35C1). This defect leads to impaired fucosylation of selectins, affecting neutrophil chemotaxis and causing recurrent infections and persistent leukocytosis.

Question 5

You have a patient presenting with neuropsychiatric symptoms, progressive chronic liver disease, Parkinsonian tremors, diminished facial expressions, and choreoathetosis. These symptoms are associated with a deficiency in which of the following? A) aquaporin B) ATP7A C) ATP7B D) Na⁺ / K⁺ -ATPase E) SLC40A1 (ferroportin)

Accepted Answer

The symptoms described are indicative of Wilson's disease, which is caused by a deficiency in the ATP7B protein, leading to copper accumulation in the liver and brain.

Question 6

Deficiency in the copper transporter ATP7A would most likely be associated with which of the following symptoms?
A) excessive thirst, dry chapped skin
B) hemochromatosis
C) hepatic failure, movement disorder such as dystonia
D) recurrent infections, severe growth retardation
E) wiry brittle hair

Accepted Answer

A deficiency in the copper transporter ATP7A is associated with Menkes disease, which is characterized by symptoms such as wiry, brittle hair due to impaired copper absorption and distribution.  Defects in ATP7A result in the Menkes disease. The clinical spectrum associated with Menkes disease includes progressive neurodegeneration, connective tissue abnormalities, and wiry brittle hair.

Question 7

Which of the following is involved in the simultaneous transport of 2 different molecules across a membrane in the same direction at the same time? A) antiporter B) a-channel C) Na⁺ / K⁺ -ATPase D) symporter E) uniporter

Accepted Answer

A symporter is a type of transport protein that moves two different molecules or ions across a membrane in the same direction simultaneously.

Question 8

GLUT4 is the glucose transporter involved in insulinstimulated glucose uptake into adipose tissue and skeletal muscle. The mechanism of glucose transport by GLUT4 is of which of the following types?
A) active transporter
B) facilitated diffusion
C) gated ion channel
D) simple diffusion

Accepted Answer

GLUT4 facilitates the transport of glucose across cell membranes via facilitated diffusion, which is a passive transport mechanism that does not require energy. Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific integral transmembrane proteins. The glucose transporters, of which GLUT4 is a member, carry out sugar transport via the mechanism of facilitated diffusion.

Question 9

Cardiotonic steroids, produced by the adrenal glands, heart tissue, and hypothalamus are specific inhibitors of which of the following? A) aquaporins B) F-type ATPases C) Na⁺ / K⁺ -ATPase D) P-type ATPases E) SLC type transporters

Accepted Answer

Cardiotonic steroids specifically inhibit the Na⁺ / K⁺ -ATPase, which is a type of P-type ATPase responsible for maintaining the electrochemical gradients of sodium and potassium ions across the cell membrane.

Question 10

Ouabain is a poisonous compound found in the ripe seeds of the African plant Strophanthus gratus. This compound is poisonous due to the fact that it is a potent inhibitor of which of the following? A) aquaporins B) F-type ATPases C) Na⁺ / K⁺ -ATPase D) P-type ATPases E) SLC type transporters

Accepted Answer

Ouabain is a potent inhibitor of the Na⁺ / K⁺ -ATPase, which is an enzyme responsible for maintaining the electrochemical gradient across the cell membrane by pumping sodium out and potassium into the cell.

Question 11

Intestinal epithelial cells possess 2 transport mechanisms to move glucose across the plasma membrane, a facilitated glucose carrier (GLUT2) as well as a sodium-dependent secondary active transporter (SGLT1). Which of the following attributes distinguishes these 2 transport modalities with respect to net glucose transport?
A) GLUT2 directly depends on ATP hydrolysis
B) GLUT2 is sensitive to competitive substrate inhibition
C) SGLT1 can transport glucose from a region of low to a region of high concentration
D) SGLT1 is carrier mediated
E) SGLT1 is saturable

Accepted Answer

SGLT1 is a Na⁺-dependent glucose cotransporter. Within the kidney tubule, the Na⁺ / K⁺ -ATPase pump on the basolateral membrane of the proximal tubule cell uses ATP to move Na+ outward into the blood, while bringing in 2 K⁺. This creates a downhill Na+ gradient inside the proximal tubule cell in comparison to both the blood and the tubule. SGLT1 uses the energy from this downhill Na+ gradient created by the ATPase pump to transport glucose across the apical membrane against an uphill glucose gradient

Question 12

Cardioactive steroids, like digoxin, exert a positive ionotropic effect on heart muscle cells. Because of this activity they can be used clinically to increase contraction of a failing heart. Which of the following proteins is important in the mechanism of action of digoxin on the cardiac muscle cell? A) N-type calcium channels B) Na⁺ / Ca²⁺ exchange protein (NCX) C) plasma membrane calcium ATPase (PMCA) D) potassium channels E) sodium channels

Accepted Answer

Digoxin inhibits the Na⁺/K⁺ ATPase, leading to increased intracellular Na⁺, which reduces the activity of the Na⁺/Ca²⁺ exchanger (NCX), resulting in increased intracellular Ca²⁺ and enhanced cardiac contractility.

Question 13

Which of the following proteins uses the sodium electrochemical gradient to actively transport a solute into the cell? A) calcium-ATPase B) GLUT2 C) Na⁺ / K⁺ ATPase D) Na⁺ / Ca²⁺ countertransport protein E) SGLT1

Accepted Answer

SGLT1 (Sodium-glucose linked transporter 1) uses the sodium electrochemical gradient to actively transport glucose into the cell against its concentration gradient.

Question 14

A 3-day-old male neonate is diagnosed with meconium ileus. You should be concerned that he has which of the following conditions?
A) alkaptonuria
B) cystic fibrosis
C) hemophilia A
D) phenylketonuria
E) Wilson disease

Accepted Answer

Meconium ileus is often associated with cystic fibrosis, a genetic disorder affecting the lungs and digestive system.  Meconium ileus is a very common early clinical expression of cystic fibrosis. Increased sodium chloride level in sweat confirms the diagnosis. About 70% of children with cystic fibrosis have a depletional abnormality of chromosome 7 which disrupts the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR is a member of the ATP-binding cassette (ABC) family of membrane transporters. Specifically, CFTR is a chloride channel expressed in numerous epithelial cell membranes. In addition to the classic pulmonary obstruction resulting from loss of CFTR function, cystic fibrosis is associated with pancreatic insufficiency, recurrent pulmonary infections, and biliary obstruction.

Question 15

You are studying the electrophysiological characteristics of cardiac pacemaker cells. Which of the following is the primary determinant of the resting membrane potential in these cells?
A) background potassium conductance
B) background sodium conductance
C) delayed rectifier potassium current
D) sodium-calcium exchange current
E) transient outward current

Accepted Answer

The resting membrane potential in cardiac pacemaker cells is primarily determined by the background potassium conductance, which helps maintain the negative charge inside the cell relative to the outside. The resting membrane potential of cardiac cells is caused by the difference in ionic concentrations and conductances across the membrane of the cell during an action potential. This potential is determined by the selective permeability of the cell membrane to various ions. The membrane is most permeable to K⁺ and relatively impermeable to other ions. The resting membrane potential is therefore dominated by the K⁺ equilibrium potential according to the K⁺ gradient across the cell membrane.

Question 16

You are carrying out mutational studies on membrane-associated proteins. You are particularly interested in proteins that pass through the plasma membrane of cells. Alteration of which of the following properties of an integral membrane protein would most likely interfere with its ability to become membrane associated?
A) the ability to bind carbohydrates on both sides of the membrane
B) the ability to move laterally in the plane of the membrane
C) the ability to translocate across the bilayer of the membrane when the temperature is increased
D) flip-flopping across the bilayer of the membrane when the temperature is increased
E) high solubility in strong basic solutions

Accepted Answer

Integral membrane proteins are permanently attached to a given biological membrane. The most common type of integral membrane protein is the transmembrane protein which spans the entire biological membrane. Integral membrane proteins possess a region of hydrophobic amino acids that allows interaction with the lipid interface of the membrane. For this reason, this class of protein can move laterally in the membrane, but cannot translocate across nor flip-flop within the membrane.

Question 17

You are examining the characteristics of ion movement in cells in culture. You find that addition of a particular compound to the medium interferes with this movement. The compound you are using most likely interferes with the function of which of the following structures that allows ion and small molecule passage directly from the cytosol of one cell to another?
A) belt desmosome (zonula adherens)
B) chemical synapse
C) desmosome (macula adherens)
D) gap junction
E) tight junction (zonula occludens)

Accepted Answer

Gap junctions are specialized structures that allow ions and small molecules to pass directly from the cytosol of one cell to another, facilitating intercellular communication.  Gap junctions do not seal membranes together, nor do they restrict the passage of material between membranes. Rather, gap junctions are composed of arrays of small channels that permit small molecules to shuttle from one cell to another and thus directly link the interior of adjacent cells. Importantly, gap junctions allow electrical and metabolic coupling among cells because signals initiated in one cell can readily propagate to neighboring cells

Question 18

Drugs that inhibit the plasma membrane Na⁺ / K⁺ ATPase decrease which of the following cellular processes? A) cell-to-cell communication via gap junctions B) cellular uptake of iron by reticulocytes C) endocytosis of low-density lipoproteins D) export of calcium from cardiac muscle cells E) transport of glucose into adipose tissue cells

Accepted Answer

Inhibition of the Na⁺ / K⁺ ATPase affects the sodium gradient, which is crucial for the function of the sodium-calcium exchanger. This exchanger helps export calcium from cardiac muscle cells, so its function is decreased when the ATPase is inhibited.

Question 19

Acetylcholine exerts effects on several cell types. On certain cells, such as muscle, the activity of acetylcholine results in the opening of which of the following types of membrane channels? A) Ca²⁺-activated K⁺ channel B) transmitter-gated cation channel C) transmitter-gated Cl^- channel D) voltage-gated Ca²⁺ channel E) voltage-gated Na⁺ channel

Accepted Answer

Acetylcholine binds to nicotinic receptors on muscle cells, which are transmitter-gated cation channels, leading to the opening of these channels and allowing the influx of Na⁺ and efflux of K⁺, resulting in muscle contraction.

Question 20

You are examining a 17-year-old adolescent girl presenting with decreased range of motion, redness, and swelling of the joints due to arthritis. The young woman also presents with xanthomas in the Achilles tendon and extensor tendons of the hand. Additional examination indicates splenomegaly. Analysis of serum shows very high levels of sitosterol, campesterol, stigmasterol, and avenosterol. You suspect the patient is suffering from sitosterolemia. Which of the following class of transport systems is likely to be defective in this patient?
A) ABC transporters
B) aquaporins
C) gap junctions
D) sodium-potassium ATPases
E) SLC transporters

Accepted Answer

Sitosterolemia is caused by mutations in the ABCG5 or ABCG8 genes, which encode for ABC transporters responsible for the efflux of plant sterols from enterocytes and hepatocytes.  Sitosterolemia is a rare autosomal recessively inherited disorder characterized by hyperabsorption and decreased biliary excretion of dietary sterols leading to hypercholesterolemia, tendon and tuberous xanthomas, premature development of atherosclerosis, and abnormal hematological and liver function test results. The disorder is caused by mutations in either of the 2 ABC transporter proteins of the obligate heterodimer composed of ABCG5 and ABCG8

Quiz 7: Biological Membranes and Membrane Transport

Digoxin is a member of the cardiac glycoside family of drugs. This drug can be used to treat patients with atrial fibrillation since it slows heart rate. Cardiac glycosides function by inhibiting which class of membrane transporter?

Aquaporins are a class of transporters that are involved in the transport of water across membranes. The aquaporins belong to which type of transporter family?

A patient who presents with unique facial features, recurrent infections, persistent leukocytosis, defective neutrophil chemotaxis, and severe growth and mental retardation would likely be manifesting these symptoms due to a deficiency in which of the following transport proteins?

You have a patient presenting with neuropsychiatric symptoms, progressive chronic liver disease, Parkinsonian tremors, diminished facial expressions, and choreoathetosis. These symptoms are associated with a deficiency in which of the following?

Deficiency in the copper transporter ATP7A would most likely be associated with which of the following symptoms?

Which of the following is involved in the simultaneous transport of 2 different molecules across a membrane in the same direction at the same time?

GLUT4 is the glucose transporter involved in insulinstimulated glucose uptake into adipose tissue and skeletal muscle. The mechanism of glucose transport by GLUT4 is of which of the following types?

Cardiotonic steroids, produced by the adrenal glands, heart tissue, and hypothalamus are specific inhibitors of which of the following?

Ouabain is a poisonous compound found in the ripe seeds of the African plant Strophanthus gratus. This compound is poisonous due to the fact that it is a potent inhibitor of which of the following?

Which of the following proteins uses the sodium electrochemical gradient to actively transport a solute into the cell?

A 3-day-old male neonate is diagnosed with meconium ileus. You should be concerned that he has which of the following conditions?

You are studying the electrophysiological characteristics of cardiac pacemaker cells. Which of the following is the primary determinant of the resting membrane potential in these cells?

Drugs that inhibit the plasma membrane Na+ / K+ ATPase decrease which of the following cellular processes?

Acetylcholine exerts effects on several cell types. On certain cells, such as muscle, the activity of acetylcholine results in the opening of which of the following types of membrane channels?

Drugs that inhibit the plasma membrane Na⁺ / K⁺ ATPase decrease which of the following cellular processes?