Transport Across Biological Membranes Flashcards
Which of the following BEST decribes the plasma cell membrane?
A. Hydrophobic
B. Lipophilic
C. Positively-charged outer core
D. All of the above
D
Which of the following requires ATP for passage of molecules across the membrane?
A. Diffusion
B. Exocytosis
C. Filtration
D. Osmosis
B
A decrease in which of the following will increase the net rate of diffusion across a lipid bilayer?
A. Membrane thickness
B. Surface area of the membrane
C. Concentration gradient
D. Oil:water content
A
What differentiates primary from secondary active transport?
A. Concentration gradient
B. Membrane carrier-protein
C. Potassium influx
D. Source of energy
D
If normal RBC osmolarity is 280 mOsm, placing it in a solution of 280mM NaCl will produce
A. Burr cells
B. Crenated cells
C. Ghost cells
D. Normal cells
D
An increase in which of the following will increase filtration across the membrane?
A. Arterial hydrostatic pressure
B. Arterial oncotic pressure
C. Venous hydrostatic pressure
D. Venous oncotic pressure
A
Transepithelial transport seen in renal and intestinal
membranes involves
A. Active transport
B. Passive transport
C. Both of the above
D. None of the above
C
Formation of water channels in the membrane is
through the process of
A. Carrier-mediated transport
B. Exocytosis
C. Phagocytosis
D. Pinocytosis
B
The forces that determine the direction in which a charged solute tends to move spontaneously across a membrane
Chemical gradient and membrane potential, together called the electrochemical gradient or elecrochemical potential
What is the chemical gradient?
The difference in solute concentration of two substances separated by a permeable membrane
What is Vm?
Membrane potential or electric gradient, the difference of opposite charged ions separated by a permeable membrane
The tendency of the force produced by Vm is to oppose ion movements that increase Vm and to drive ion movements that reduce Vm. T/F
T
In accordance with the second law of thermodynamics, Vm must be decreased
What is the importance of membrane proteins in transport of solutes?
Transmembrane passage of polar and charged solutes requires a very high energy of activation. Membrane proteins lower the activation energy for the transport of polar and charges solutes by providing an alternative path through the membrane.
What drives passive transport?
Electochemical gradient
Active transport is thermodynamically unfavorable (endergonic) and takes place only when coupled (directly or indirectly) to an exergonic chemical reaction. T/F
T
In primary active transport, solute accumulation is coupled directly to which chemical reaction?
Hydrolysis of ATP: conversion of ATP to ADP + P
Transport occuring when endergonic transport of one solute is coupled to the exergonic flow of a different sollute that was originally pumped by primary active transport
Secondary active transport
What drives secondary active transport?
Energry from the exergonic reaction of primary active transport
What is Fick’s first law of diffusion?
J= -DA (ΔC/ΔX)
In Fick’s first law of diffusion, J= -DA (ΔC/ΔX), what does each symbol stand for?
J= flux or rate of diffusion per unit time D= diffusion coefficient A= area across which the diffusion is occurring ΔC= concentration gradient ΔX = distance along which the diffusion is occurring
In J= -DA (ΔC/ΔX), which symbol accounts for the thickness of the membrane?
ΔX
In J= -DA (ΔC/ΔX), which symbol accounts for the area of the membrane?
A
In J= -DA (ΔC/ΔX), which symbol accounts for the concentration of the solute?
ΔC
What is this known as J= -DA (ΔC/ΔX)?
Ficks first law of diffusion
In J= -DA (ΔC/ΔX), how is D approximated?
Using Stokes-Einstein equation:
D= -(kT)/(6πvr)
What is the Stokes-Einstein equation?
D= -(kT)/(6πvr)
In D= -(kT)/(6πvr), what do the symbols stand for?
k = Boltzman’s constant T = absolute temperature (K) r= radius of the molecule v = viscosity of medium
Faster rate of diffusion results the higher which of these factors are?
A. Thickness of membrane B. Molecular size C. Membrane surface area D. Steepness of concentration gradient E. Temperature F. Lipid content G. All of the above H. None of the above
C, D, E, F
Thinner membrane, and smaller molecular size increases rate of diffusion
Osmotic pressure is determined by what factor?
Number of molecules in the solution
Osmotic pressure is dependent on size and mass of molecules. T/F
F
It is solely determined by the number of molecules in the solution
How is osmotic pressure calculated?
van’t Hoff’s Law
π = nCRT
This equation π = nCRT is called what?
van’t Hoff’s Law
van’t Hoff’s Law calculates what?
Osmotic pressure
The symbols in π = nCRT stand for what?
n= number of dissociable particles per molecule C= total solute concentration R= gas constant T= temperature in degrees Kelvin
What is the difference between osmolarity and osmolality?
Osmolarity refers to the osmotic pressure generated by dissolved solute molecules in 1 L of solvent. Osmolality refers to the osmotic pressure in 1 kg solvent.
Osmolality is dependent on temperature. T/F
F
Osmolality is based on mass of the solvent. Since mass is independent of temperature, osmolality is not affected by temperature.
What is an isotonic solution?
A solution that does not change the volume of a cell when cell is submerged in, due to equal tonicity of that solution to the fluid inside the cell
What is a hypotonic solution?
A solution that causes the cell to swell when cell is submerged in, due to lesser tonicity of that solution than the fluid inside the cell
What is a hypertonic solution?
A solution that causes the cell to shrink when cell is submerged in, due to greater tonicity of that solution than the fluid inside the cell
Osmosis, which is the passive diffusion of water, occurs via which system?
a) protein channel
b) protein carrier
c) lipid bilayer
d) pinocytosis
A
Which of the following will increase the rate of diffusion through the lipid bilayer?
A. Greater surface area
B. Larger molecule
C. More polar molecule
D. Lower temperature
A
Which of the following is the LEAST physiologically important route for the movement of calcium ions across plasma membranes?
A. Primary active transport
B. Secondary active transport
C. Diffusion through ion channels
D. Diffusion through the lipid bilayer
D
Which is TRUE about diffusion through membrane channels?
A. Movement through the channels is nonselective.
B. Changing the membrane potential could alter the rate of diffusion.
C. The rate of movement of ions is predicted by their lipid solubility.
D. Transport through membrane channels is slower than facilitated diffusion.
B
Uphill transport or movement from a region of lower concentration to that of a higher concentration is possible in which of the following?
A. Diffusion through the lipid bilayer
B. Diffusion through protein channels
C. Facilitated diffusion
D. Primary active transport
D
Which of the following transport mechanisms exhibits chemical specificity?
A. Facilitated diffusion
B. Diffusion through protein channels
C. Secondary active Transport
D. All of the above
D
Transport of Substance X does NOT observe saturation kinetics. Which is its MOST LIKELY transport mechanism?
A. Diffusion through protein channels
B. Facilitated diffusion
C. Primary active transport
D. Secondary active transport
A
Saturation kinetics refers to the amount of substrate a protein carrier can transport.
A cell, placed in a solution, swells and bursts. Assuming a normal cellular osmolarity of 280 mOsm, into which solution could the cell have been placed?
A. 140 –mM NaCl solution
B. 280- mM NaCl solution
C. 280-mM glucose solution
D. A solution of pure water
D
The use of glucose in oral rehydration solutions facilitates the absorption of Na+ ions into the enterocytes (small intestinal cell) through which membrane transport mechanism?
A. Primary active transport
B. Secondary active transport
C. Facilitated diffusion
D. Diffusion through protein channels
B
Insulin-mediated glucose uptake into muscle and adipose cells is mediated through which transport mechanism?
A. Primary active transport
B. Secondary active transport
C. Facilitated diffusion
D. Diffusion through protein channels
C
The movement of glucose through the basolateral membrane of a small intestinal cell into the bloodstream is mediated through which of the following?
A. Primary active transport
B. Secondary active transport
C. Facilitated diffusion
D. Exocytosis
C
Hormones like insulin are commonly secreted from cells by means of vacuolar transport. Which of the following configurations of phospholipids is MOST relevant in this form of transport?
A. Micelles
B. Monolayers
C. Bilayers
D. A & C
C
Endergonic reactions are driven to completion inside the cell
a. By coupling with an exergonic reaction
b. Increasing enzyme concentration
c. Increasing ADP
A
A red blood cell shrinks by 1.5 times its original size, what is the concentration of sodium ions?
a. 90 mEq/L
b. 150 mEq/L
c. 200 mEq/L
d. 400 mEq/L
C
Which of the following solute transport mechanisms differentiates the villous and cryptic parts of the small intestine?
a. Osmosis
b. Primary active transport
c. Secondary active transport
d. Simple diffusion
C
What is oncotic pressure?
Osmotic pressure exerted by large molecules in solution
Like omotic pressure, oncotic pressure conforms to van’t Hoff’s law. T/F
F
Oncotic pressure does not conform to Van’t Hoff’s law. Why this is is no completely understood, but appears to be related to the size and shape of the protein molecule
Which ions primarily determines the osmolality of ECF?
Na (and its attendant ions Cl and HCO3), because it is the most abundant ion in the ECF
Osmolality can be obtained by simply doubling the sodium concentration. T/F
T
How is the composition of interstitial fluid and plasma different?
Plasma has more proteins
The fluid exchange between the ECF and ICF are determined by which forces?
Oncotic pressure and hydrostatic pressure
Which pressure differences between ICF and ECF cause movement of fluid into and out of cells? Why?
Osmotic pressure,
because hydrostatic pressure is not present across the cell membrane. The plasma membrane contains water channels, making water easily cross the membrane, which changes the osmolality of either ICF or ECF.
What happens to the ICF and ECF of a cell when 290 mOsm/kg NaCl solution is added to the ECF?
No net movement
What happens to the ICF and ECF of a cell when 145 mOsm/kg NaCl solution is added to the ECF??
ICF and ECF volumes increase, but there is greater increase in ECF.
There would be net movement of water to ICF as the result of the decreased osmolality in the ECF. Osmolalities become equal between the two compartments, after movement of water.
What happens to the ICF and ECF of a cell when 1000 mOsm/kg NaCl solution is added to the ECF?
ICF volume decreases, ECF increases
There would be net movement of water into ECF, as the result of its increased osmolality. Osmolalities become equal between the two compartments, after movement of water.
What is the functional unit of gap junctions?
Connexon, composed of six integral membrane protein subunits called connexins
In which membrane domain are NA-K-ATPase located?
Basolateral
In which membrane domain are the K channels located?
Either
Transport of material from basolateral to apical membrane
Secretion
Transport of material from apical to basolateral membrane
Absorption/reabsorption
Transcellular transport: active or passive?
Active
Transcellular transport is a two-step process. First is the passive entrance of Na into cell driven by the chemical gradient. Second is the active exit of Na into the cell driven by Na-K-ATPase. Because the gradient in the first step is achieved through the active transport via Na-K-ATPase, trancellular transport is considered active.
Paracellular transport: active or passive?
Passive
The driving forces for the solute is transepithelial concentration gradient, and if solute is charged, transepithelial voltage
What is transcellular transport?
It is the transportation of solutes and water across the apical and basolateral membranes
What is paracellular transport?
It is the transportation of solutes and water between cells across tight junctions
Any solute that is transported actively across epithelium must be transported through transcellular or paracellular transport?
Transcellular
Transepithelial transport processes set up the transepithelial chemical and voltage gradients which in turn dirve paracelular transport. T/F
T
Which of these substances can readily diffuse across the cell membrane?
A. Amino acid
B. Carbon dioxide
C. Glucose
D. Sodium ions
B
Which of the following events occurs during osmosis with a
membrane impermeable to solutes?
A. Water molecules are pumped by active transport.
B. Water molecules diffuse down from a region of high solute concentration to a region of low solute concentration.
C. The fluid volume on both sides of the membrane is unchanged.
D. The fluid osmolarity on both sides of the membrane is the same after osmosis.
D
Digoxin, a digitalis glycoside is used in the treatment of heart failure by pharmacologically blocking the Na+/K+ pump in cardiac muscle. Which of the following is the result of this block?
A. A net increase in the intracellular potassium concentration
B. An increased electrochemical gradient for Na+ influx across the cell membrane
C. A reduced activity of the sodium-calcium exchanger
D. A reduced supply of intracellular calcium
C
Which best describes Na-K Pump?
A. Composed of three alpha-subunit proteins and 2 beta-
subunit proteins
B. Exchanges three intracellular Na+ ions for two extracellular K+ ions
C. Generates positive
D. Symport process
B
Which does not describe secondary active transport?
A. Derives energy from glucose concentration differences across the cell membrane
B. Rate limiting, saturable
C. Can be an antiport or symport
D. Participates in absorption of sugars and amino acids in the GI tract
C
Which is not affected by disturbance of ATP synthesis?
A. Cholesterol regulation
B. Formation of ultrafiltrate
C. Neurotransmitter secretion
D. WBC phogocytosis
B
A patient is diagnosed with diabetes inspidus which is caused by a deficiency in vasopressin, an antidiuretic hormone. What type of membrane transport is affected?
A. Diffusion
B. Endocytosis
C. Exocytosis
D. Osmosis
C
A patient is diagnosed with diabetes inspidus which is caused by a deficiency in vasopressin, an antidiuretic hormone. If his serum sodium is 190 mEq/L, what will be the final volume of his red blood cell if the initial serum osmolarity is 285 mOsm/kg H20 assuming that the effect of glucose and BUN is negligible?
A. Decreased to 3⁄4 of its original volume
B. Increased by 1.5 times to its initial volume
C. No change in size
D. Insufficient data to calculate final volume
A
A patient is diagnosed with diabetes inspidus which is caused by a deficiency in vasopressin, an antidiuretic hormone. He is dehydrated but there are no signs of shock. Which replacement is physiologically appropriate?
A. Salt Tablets
B. Isotonic saline
C. ORS
D. Water
Knowing that the flow of water is related to several factors, your answer to the above question is due to an elevated:
A) Diffusion coefficient
B) Hydraulic conductivity
C) Membrane area
D) Osmotic pressure gradient
D and D
Which of the following is true regarding the physiologic basis of ORS?
A. GLUT proteins enhance sodium absorption by coupling with glucose
B. There is greater net absorption of sodium with glucose in normal intestine
C. There is no maximal transport of glucose in intestinal cells via simple diffusion
D. Sodium channels are not affected in infectious diarrhea.
B
The homemade ORS consists of 1 tsp salt with 8 tsps of sugar in 1 liter of water. While preparing it, you inadvertently mixed 1 tsp of sugar and 8 tsps of salt instead. Which of the following will you expect to happen?
A. Increased osmolarity of the ICF
B. Low serum sodium
C. Negative gut balance of water and sodium
D. Presence of ghost and burr cells.
A
B.C. is a 20 year old male who was previously well until 20 hours prior to consult, when he developed mild abdominal cramps and passage of watery stools (2-3 cups per episode.) A family physician assessed him to have acute infectious diarrhea probably secondary to a viral etiology.
Which of the following statements MOST accurately describe the pathophysiology of his condition?
A. It is a purely osmotic phenomenon.
B. It is a purely secretory phenomenon.
C. It involves both an osmotic and secretory component.
D. It involves neither an osmotic nor a secretory component.
C
Signs of mild dehydration were detected on physical examination. Which of the following has a good scientific basis to give?
A. Distilled, pure drinking water
B. Carbonated soda
C. Intravenous fluid rehydration
D. Oral rehydration therapy
D
At baseline, C1=10 and C2=5. Using Fick’s law of Diffusion, what is the effect if C1 is reduced to half on flux?
A. More positive
B. Increase 3x
C. Decrease 3x
D. No movement
D
Which of the following does not display saturation (Michaelis-Meuten) kinetics?
A. Facilitated diffusion
B. Na-coupled active transport
C. Passive diffusion
D. Vesicular Transport
C
Diabetes insipidus is a condition where serum sodium is high. This is because
A. Transport against concentration gradient
B. Impaired exocytosis
C. No(?)/low ATP
B
Digitalis, which inhibits Na-K ATPase pump, will result in decreased intracellular
A. Calcium
B. Sodium
C. Potassium
C
The energy used to drive filtration across a semi-permeable membrane comes from
A. ATP
B. Hydrostatic Pressure
C. Kinetic Energy
D. Oncotic Pressure
D
Which of the following is true regarding transepithelial transport?
A. Solute has higher concentration at the luminal side
B. Facilitated diffusion to the vessel
C. Primary active transport predominates at the luminal side
D. Secondary active transport drives Na+ to the vessel
B
Which is correct?
A. Central Pontine Myelinosis: Diffusion
B. Dapaglifozin: Active Transport
C. Glomerulonephritis: Facilitated Diffusion
D. Myasthenia Gravis: Passive Transport
B
