Session 5 Flashcards
Which of the following channels is an example of an active transport uniporter?
A. Na-K-ATPase B. Proton pump C. NCX D. VGCC E. Na-H-exchanger
B. Proton pump
Uses ATP to transport H+ ions against their concentration gradient.
Na-K-ATPase is an example of active transport but is a co-transporter rather than uniporter. NCX depends on concentration gradients and is not a uniporter, similarly for Na-H-exchanger. VGCC is an example of facilitated diffusion via a ligand gated channel.
Controlling intracellular pH is vital to ensure effective protein functions (e.g. enzymes), therefore needs careful balance. Which of the following transporters buffers changes in pH only via acid extrusion?
A. Anion exchanger B. Na-H-exchanger C. Na-K-ATPase D. Na-HCO3-Cl co-transporter E. Na-HCO3 co-transporter
B. Na-H-exchanger
Uses the sodium gradient (created by Na-K-ATPase, which has an indirect rather than direct effect on pH control) to remove protons from a cell. The Na-HCO3-Cl co-transporter does both acid extrusion and alkali influx, anion exchangers cause alkali extrusion and the Na-HCO3 co-transporter causes alkali influx.
Cell shrinking or swelling can occur if fluid movement between compartments is not properly controlled.
What is the underlying principle of how cells resist cell shrinking?
Transport of osmotically active ions into the cell. This causes an osmotic gradient, where water will follow, and therefore increase intracellular volume.
The sodium pump…
A. Can be activated by metabolic poisons
B. Exchanges extracellular Na+ for intracellular K+
C. Exchanges extracellular K+ for intracellular Na+
D. Is an ion channel
E. Is important for maintaining a constant cell volume
C - Exchanges extracellular K+ for intracellular Na+
The sodium pump exchanges intracellular Na+ for extracellular K+. Although it moves ions it is not considered to be an ion channel, but a pump because it is driven by the hydrolysis of ATP and resides in the plasma membrane, it can be directly inhibited by cardiac glycosides, notably ouabain and so is inhibited by metabolic poisons. Other transporters of ions are important in controlling cell volume.
Why will increasing the excretion of sodium from the blood help a patient with high blood pressure?
Water follows osmotic gradients. By and large, there is no way of directly moving water, it has to follow the movement of osmotically active ions. Therefore, by excreting more sodium from the body, more water will follow and therefore reduce a patient’s circulating blood volume. This in turn will reduce the patient’s blood pressure.
Where in the body is a key location for regulating levels of sodium excretion?
A. Heart B. Liver C. Small intestine D. Kidney E. Saliva
D - Kidney
The major control point for sodium regulation occurs through transporters located in the kidney. This is why treatments for high blood pressure can include diuretics, acting on the kidney, to increase the amount of sodium excretion.
Gases such as O2, CO2 and N2O cross the plasma membrane by which transport process?
A. Primary active transport B. Secondary active transport C. Passive diffusion D. Facilitated diffusion E. Gas-specific membrane symporter
C - Passive diffusion
Gases are small, non-polar molecules and can cross the lipid bilayer with ease because they can interdigitate between the heads of the phospholipids. They therefore do not need specific mechanisms to cross the plasma membrane but diffuse passively down their concentration gradients (i.e. from high to low partial pressure).
What is the principle intracellular cation?
A. Na+ B. Ca2+ C. Cl- D. K+ E. Mg2+
D - K+
Sodium is the principal extracellular cation and potassium is the principal intracellular cation. Cl- is the principal extracellular anion. Mg2+ is an important cation, often found in a bound state, e.g. complexed with DNA, nucleotides or as a co-factor for enzymes.
When considering the energy requirements for the flow of a non-polar molecule across a plasma membrane, the equation ∆𝐺 = 𝑅𝑇 𝑙𝑜𝑔𝑒 𝑐2/𝑐1 is used. If C2 is 10^-5M and C1 is 10^-3M, calculate the ∆𝐺 value and comment on whether the transport process is active or passive.
∆𝐺 = +11.4 KJ/ mol. Because ∆𝐺 is a positive value, then the transport process is an active process working against a concentration gradient. If G had been a negative value, then the transport process would have been passive with the molecule moving down its concentration gradient by simple diffusion. (This concept was covered in detail within the lecture).
In peripheral tissues, CO2 is absorbed by the erythrocyte (red blood cell) and O2 is released. Which 2 ions are transported through Band 3 (AE1) on the erythrocyte plasma membrane to facilitate this gaseous transfer?
A. Bicarbonate and chloride B. Bicarbonate and sodium C. Chloride and calcium D. Calcium and hydrogen E. Sodium and hydrogen
A - Bicarbonate and chloride
CO2 is transported by erythrocytes primarily as bicarbonate. Band 3 is a bicarbonate-chloride ion antiport anion exchanger (AE1) and so as bicarbonate decreases in the cell, chloride ions enter, increase in concentration and lower intracellular pH. The acidified environment causes a conformational change in the Hb molecule and O2 is released from the cell. A can be the only correct answer because all other options include cations in their answers.
