Intracellular transport Flashcards
Question 4: What is meant by primary active transport?
A. Deliberate transport of essential substances
B. Movement of a solute across a membrane against its gradient via hydrolysis of ATP
C. Movement of intracellular molecules along actin filaments
D. Simple diffusion of essential nutrients across a biological membrane
E. Transport of nutrients in the circulation from the intestine to other tissues
: B. Movement of a solute across a membrane against its gradient via hydrolysis of ATP
Correct! Primary active transport directly uses ATP to move solutes against their concentration gradients. The Na+/K+-ATPase pump is a prime example of this.
Question 27: Which glucose transporter is found in muscle and adipocytes and is regulated by insulin?
A. Glut-1
B. Glut-2
C. Glut-3
D. Glut-4
E. Glut-5
D. Glut-4
Correct! GLUT4 is the insulin-sensitive transporter found in muscle and adipose tissue. When insulin binds to its receptor, it triggers the translocation of GLUT4 to the cell surface, increasing glucose uptake.
Question 39: Which type of curve is observed for a plot of initial velocity (y axis) vs substrate concentration (x axis) for an enzyme reaction that obeys Michaelis-Menten kinetics?
A. Exponential
B. Quadratic
C. Rectangular hyperbola
D. Sigmoid
E. Straight line of the form y=mx+c
C. Rectangular hyperbola
Correct! The relationship between substrate concentration and initial velocity in Michaelis-Menten kinetics is hyperbolic, and it is typically represented as a rectangular hyperbola on the graph.
Question 1:
What is the primary function of the Na+/K+-ATPase pump?
A. To transport Na+ into the cell and K+ out of the cell
B. To maintain the resting membrane potential by moving Na+ out and K+ in
C. To generate ATP for the cell
D. To facilitate the movement of water across the membrane
E. To regulate the pH of the cell
Take your time, and let me know your answer when you’re ready!
B
Correct! The primary function of the Na+/K+-ATPase pump is to maintain the resting membrane potential by moving Na+ out of the cell and K+ in, against their concentration gradients.
Question 2:
Which type of transport does the Na+/K+-ATPase pump use to move ions across the membrane?
A. Simple diffusion
B. Facilitated diffusion
C. Primary active transport
D. Secondary active transport
E. Passive diffusion
C
Correct! The Na+/K+-ATPase pump uses primary active transport to move ions against their concentration gradients. It requires energy from ATP hydrolysis to function.
Which of the following statements best describes facilitated diffusion?
A. It moves substances against their concentration gradient using energy.
B. It requires membrane proteins but does not require energy.
C. It is the movement of gases like oxygen through the lipid bilayer.
D. It involves the active transport of glucose into cells.
E. It only occurs through ion channels, not carrier proteins.
B
Facilitated diffusion requires membrane proteins (such as channel or carrier proteins) to move substances down their concentration gradient, but it does not require energy (ATP).
Which of the following is a secondary active transport mechanism?
A. Na+/K+-ATPase pump
B. GLUT4 transporter
C. SGLT (Sodium-Glucose Co-Transporter)
D. Aquaporins
E. K+ leak channels
C
Correct! The SGLT (Sodium-Glucose Co-Transporter) is an example of secondary active transport. It uses the sodium gradient created by the Na+/K+-ATPase pump to move glucose against its concentration gradient, without directly using ATP.
Which of the following is not involved in active transport?
A. Na+/K+-ATPase pump
B. Proton pump
C. SGLT (Sodium-Glucose Co-Transporter)
D. GLUT4 transporter
E. Ca²⁺ ATPase pump
D. GLUT4 transporter.
GLUT4 is involved in facilitated diffusion, not active transport. It moves glucose into the cell down its concentration gradient in response to insulin. It doesn’t require energy (ATP).
The other options (Na+/K+-ATPase pump, Proton pump, SGLT, and Ca²⁺ ATPase pump) all involve active transport, either directly using ATP or using an established gradient to move ions or molecules against their concentration gradients.
Which of the following molecules can move through the membrane via simple diffusion?
A. Glucose
B. Oxygen (O₂)
C. Na⁺ ions
D. Sodium chloride (NaCl)
E. Water (H₂O)
B Correct! Oxygen (O₂) can pass through the membrane via simple diffusion because it is small and non-polar, allowing it to easily diffuse across the lipid bilayer without the need for transport proteins or energy.
Which of the following factors does not affect the rate of simple diffusion?
A. Concentration gradient
B. Temperature
C. Size of the molecule
D. Presence of transport proteins
E. Lipid solubility of the molecule
D
Correct! The presence of transport proteins does not affect the rate of simple diffusion. Simple diffusion occurs without the need for transport proteins, as molecules move directly across the lipid bilayer.
Factors that do affect simple diffusion include:
The concentration gradient (the greater the difference, the faster the diffusion),
Temperature (higher temperature increases the rate),
Size of the molecule (smaller molecules diffuse faster),
Lipid solubility (more hydrophobic molecules diffuse more easily).
Which of the following is true about the Na+/K+-ATPase pump?
A. It moves 2 Na⁺ ions into the cell and 3 K⁺ ions out of the cell.
B. It requires energy in the form of GTP.
C. It helps maintain a high Na⁺ concentration inside the cell.
D. It is a form of secondary active transport.
E. It moves 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell.
E Correct! The Na+/K+-ATPase pump moves 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, both against their concentration gradients. This process is powered by the hydrolysis of ATP.
Question 11:
What is the role of insulin in the function of GLUT4 transporters?
A. It triggers the translocation of GLUT4 to the plasma membrane.
B. It phosphorylates GLUT4 to increase its activity.
C. It inhibits the function of GLUT4 transporters.
D. It decreases glucose uptake by muscle and adipose tissue.
E. It stimulates the production of new GLUT4 transporters in the cell.
A
Correct! Insulin triggers the translocation of GLUT4 to the plasma membrane, which increases glucose uptake into muscle and adipose tissues. This process helps regulate blood glucose levels, especially after meals.
Which of the following types of transport requires energy but does not involve a membrane protein?
A. Primary active transport
B. Secondary active transport
C. Facilitated diffusion
D. Simple diffusion
E. None of the above
Correct! The answer is E. None of the above.
Every type of transport that requires energy, including primary active transport and secondary active transport, involves membrane proteins. Simple diffusion and facilitated diffusion do not require energy, but facilitated diffusion does require membrane proteins.
Which of the following best describes secondary active transport?
A. It directly uses ATP to move substances against their concentration gradient.
B. It requires a membrane protein and energy from another ion gradient.
C. It involves the movement of water across the membrane.
D. It is a passive process that does not require energy.
E. It moves substances down their concentration gradient only.
B
Correct! Secondary active transport requires a membrane protein and uses the energy stored in an ion gradient (created by primary active transport) to move substances against their concentration gradient. The energy is not directly from ATP, but rather from the ion gradient established by processes like the Na+/K+-ATPase pump.
Digitoxin/Digoxin mechanism
Inhibit Na+/K+ pump by preventing dephosphorylation step.
↑ Intracellular Na+ → reduced Na+ gradient.
Reduces Ca2+ export via Na+/Ca2+ exchanger → ↑ intracellular Ca2+ → ↑ cardiac muscle contraction.
Used in heart failure.
Ouabain
Plant extract; inhibits Na+/K+ pump by blocking K+ binding.
Similar downstream effects to digitoxin.
Cystic Fibrosis (CF)
Mutation in CFTR protein, a Cl- channel of the ABC transporter family.
CFTR is ATP-gated, opened via PKA-mediated phosphorylation.
Defective Cl- transport → ↓ water movement → thick mucus.
Leads to chronic lung infections and blocked ducts.
Cholera
Vibrio cholerae toxin ↑ intracellular cAMP by activating adenylate cyclase.
cAMP activates CFTR → massive Cl- secretion into gut lumen.
Na+ and water follow osmotically and paracellularly → profuse diarrhoea.
Oral rehydration therapy uses glucose to drive Na+ (and hence Cl- and water) uptake via SGLT.
