Deck 7: Biological Membranes and Membrane Transport

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

Answer 1

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

Answer 2

a-channels

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)

Answer 3

A
EXPLANATION: Nephrogenic diabetes insipidus (NDI) is a disorder in which a defect in the tubules in the kidneys causes a person to pass a large amount of urine. This disorder is caused by an improper response of the kidney to antidiuretic hormone (ADH, also called vasopressin), leading to a decrease in the ability of the kidney to concentrate the urine by removing free water. The primary cause of NDI is a mutation in the ADH receptor in the kidney. However, NDI can also result from mutations in the aquaporin-2 gene.

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

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)

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

Question 21

Certain types of cell junctions render epithelial cells impermeable. Which of the following types of cell junction is responsible for impermeability, therefore requiring transcellular movement of substances from the apical surface to the basolateral surface of the epithelium?

A) desmosome (macula adherens)
B) belt desmosome (zonula adherens)
C) fascia adherens
D) gap junction
E) tight junction (zonula occludens)