quiz cell physiology Flashcards
Which ONE of the following statements regarding communication between cells of the body is CORRECT?
Select one:
- Gap junction proteins are critical elements in neurotransmitter-mediated communication between adjacent cells.
- Chemical communication can occur via metabotropic or ionotropic signaling with metabotropic signaling being more suited for very fast (1-2 ms) synaptic communication between nerve cells.
- At the mammalian neuromuscular junction, the neurotransmitter is released from nerve terminals by a Na+ dependent counter-transporter.
- The same neurotransmitter can only signal via either metabotropic or ionotropic receptors.
- At the mammalian neuromuscular junction, enzymatic breakdown plays a major role in terminating the actions of acetylcholine on its receptors.
At the mammalian neuromuscular junction, enzymatic breakdown plays a major role in terminating the actions of acetylcholine on its receptors.
The enzyme acetylcholinesterase breaks down acetylcholine and is the main mechanism by which the neurotransmitter’s actions are terminated (there is also some lateral diffusion away from the synapse).
If a substance is moving from inside a cell to outside via simple diffusion then which ONE of the following is CORRECT?
Select one:
- Its transport rate will quickly saturate because the binding sites on the membrane transporter involved becomes fully occupied.
- If the substance is uncharged, then its extracellular concentration must be greater than its intracellular concentration.
- Its transport across the membrane requires coupling to the transport of a second substance down it’s pre-existing electrochemical gradient.
- Its transport is likely to be mediated by exocytosis of a vesicle containing the solute.
- Its transport rate is directly proportional to the substance’s lipid solubility (partition co-efficient).
Its transport rate is directly proportional to the substance’s lipid solubility (partition co-efficient).
From Fick’s Law.
(It states that ‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’.
A sensory nerve cell in the skin of the finger is quiescent (not firing action potentials) with a steady resting membrane potential of -70 mV. This nerve cell detects when the finger touches something, responding to touch by firing a burst of action potentials. This signal is then transmitted to the somatosensory cortex in the brain where the sense of touch is perceived. In regard to this sensory nerve cell, which ONE of the following options is most likely to be CORRECT?
Select one:
- The sensory nerve cell becomes hyperpolarized in response to the touch stimulus.
- The touch causes the membrane potential of this sensory nerve cell to cross the threshold for activation of voltage-dependent Na+ and K+ channels.
- At all times (i.e. both before and during touch), the membrane of the sensory nerve cell is likely to be more permeable to K+ as compared to Na+.
- When the finger touches the object, an IPSP (inhibitory postsynaptic potential) occurs in the sensory nerve cell.
- The response of the sensory nerve cell is transmitted to the brain via passive or electrotonic propagation of action potentials via the sensory nerve and spinal cord.
The touch causes the membrane potential of this sensory nerve cell to cross the threshold for activation of voltage-dependent Na+ and K+ channels.
The fact that the nerve fired an action potential in response to touch indicates that it must have been depolarized beyond the threshold for activation of the voltage-dependent Na+ and K+ channels.
A healthy young man drinks a sports supplement containing glucose and creatine which is advertised to “enhance muscle endurance by increasing intracellular ATP and Na-pump activity”. Assuming this “Na-pump” refers to the Na+/K+/ATPase, which ONE of the following options is MOST CORRECT?
Select one:
- The Na+/K+/ATPase will transport glucose (along with K+) into the muscle fibre to generate ATP and Na+.
- The Na+/K+/ATPase actively transports K+ ions out of a cell and Na+ ions into the cell.
- Increased ATP concentration allows a greater passive flux of K+ and Na+ via the Na+/K+/ATPase.
- A sustained and significant increase in the activity of the Na+/K+/ATPase would not have any effect on the intracellular ion concentrations.
- An increase in Na+/K+/ATPase activity would be expected to lead to a decrease in the intracellular free Ca2+ concentration due to an increased activity of a secondary active transporter that exchanges Na+ influx for Ca2+ efflux.
An increase in Na+/K+/ATPase activity would be expected to lead to a decrease in the intracellular free Ca2+ concentration due to an increased activity of a secondary active transporter that exchanges Na+ influx for Ca2+ efflux.
An increase in Na+/K+/ATPase activity should result in increased pumping out of Na+ thus generating a greater electrochemical force for Na+/ Ca2+ exchange. In fact, blocking the Na+/K+/ATPase can be used to increase intracellular Ca2+ and aid cardiac muscle contraction in congestive heart disease.
Which ONE of the following statements regarding action potential propagation in nerve cells is CORRECT?
Select one:
- Myelination decreases the conduction velocity of action potential propagation
- There is a greater leak of local current flow across the cell membrane in a myelinated axon as compared to an unmyelinated axon.
- In a normal unmyelinated axon, the action potential amplitude gets progressively smaller as it travels along the axon towards the nerve terminal.
- Action potentials are initiated in the axon hillock and can then propagate both forward towards the axon terminal and backwards into the nerve dendrites.
- Saltatory conduction is where the action potential “jumps” from node to node and occurs in all mammalian nerve axons.
Action potentials are initiated in the axon hillock and can then propagate both forward towards the axon terminal and backwards into the nerve dendrites.
Action potentials start in a specialized region of the axon close to the soma called the axon hillock, and can propagate towards the nerve terminal and also back into the nerve dendrites (“back propagation”).
The diagram below shows a schematic nerve cell bathed in intracellular and extracellular solutions at 37°C and with the concentrations of Na+ and K+ as shown. The cell membrane contains a population of K+-selective ion channels and a separate population of Na+-selective ion channels as indicated. An electrode is inserted into the cell that measures the membrane potential (Vm). The Nernst equation for ion x at 37°C, can be simplified to: Ex = 62 mV log10 [ionoutside] / [ioninside].
Extracellular concentrations:
[K+]outside = 14 mM
[Na+]inside = 140 mM
Intracellular concentrations:
[K+]outside = 140 mM
[Na+]inside = 14 mM
If initially (at rest) only the K+ channels are open, and then the Na+ channels also open, which ONE of the following options MOST CLOSELY describes the membrane potential (Vm):
Select one:
- Resting Vm = -62 mV, when the Na+ channels open, Vm becomes depolarized
- Resting Vm = +62 mV, when the Na+ channels open, Vm becomes hyperpolarized
- Resting Vm = +62 mV, when the Na+ channels open, Vm becomes depolarized
- Resting Vm = 0 mV, no change when Na+ channels open
- Resting Vm = -62 mV, when the Na+ channels open, Vm becomes hyperpolarized.
Resting Vm = -62 mV, when the Na+ channels open, Vm becomes depolarized
E= (RT/zF) log(Co/Ci)
- > it’ll be log(14/140) bc only K+ open
- > then when Na+ opens, Vm becomes depolarise (ie AP are fired)
Which ONE of the following statements regarding membrane transport processes is CORRECT?
Select one:
- A K+ ion can only move through an ion channel in a direction that is down its electrochemical gradient.
- The SGLT protein that couples Na+ influx with the movement of glucose into cells against its concentration gradient is an example of a facilitated diffusion protein.
- The hormone insulin is released from pancreatic beta-cells into the bloodstream by endocytosis.
- The Ca2+/Na+ exchanger (counter-transporter) that couples Ca2+ efflux with Na+ influx, directly utilizes ATP as an energy source.
- The Na+/K+/ATPase is an example of a secondary active transporter.
A K+ ion can only move through an ion channel in a direction that is down its electrochemical gradient.
An ion channel is an example of facilitated diffusion, so the substance always moves down its chemical gradient (if solute is uncharged) or electrochemical gradient (if solute is charged).
A nerve cell contains intracellular K+ and Na+ concentrations of 140 mM and 10 mM, respectively. It is surrounded by an extracellular solution containing K+ and Na+ concentrations of 4 mM and 150 mM, respectively. The only open ion channels in the nerve cell are selective for K+. Given that R= the Gas constant, T = temperature in Kelvins, F = Faraday’s constant and z = valence, the nerve cell’s membrane potential can be calculated as:
Select one:
- (RT) / (zF) multiplied by loge [(10 mM + 140 mM) / (4 mM + 150mM)]
- (RT) / (zF) multiplied by loge (10 mM / 150 mM)
- (RT) / (zF) multiplied by loge (140 mM / 4 mM)
- (RT) / (zF) multiplied by loge (4 mM / 140 mM)
- (RT) / (zF) multiplied by loge [(150 mM + 4 mM) / (10 mM + 140 mM)]
(RT) / (zF) multiplied by loge (4 mM / 140 mM)
The cell is only permeable to K+, so the membrane potential will quickly go to the K+ equilibrium potential, given by the Nernst equation.
Consider an experiment where a small amount of blue-coloured copper sulphate (CuSO4) salt is added to a mixture of water and paraffin oil and the solution is shaken so that the molecules making up the salt become hydrated by some of the other molecules in this solution. Complete the sentence with ONE of the following options: The CuSO4 becomes hydrated by:
Select one:
- polar water molecules giving rise to Cu2+ anions and SO42- cations.
- non-polar oil molecules giving rise to Cu2+ anions and SO42- cations
- polar water molecules giving rise to Cu2+ cations and SO42- anions.
- non-polar water molecules giving rise to Cu2+ cations and SO42- anions.
- polar oil molecules giving rise to Cu2+ anions and SO42- cations
polar water molecules giving rise to Cu2+ cations and SO42- anions.
- ions have polarity
- 2+ is cation, 2- is anion
The diagram below shows a typical Action Potential in a nerve cell in the brain. In regards to this action potential, which ONE of the following is MOST CORRECT?
Select one:
- The action potential consists of a rapid hyperpolarization, followed by a slower depolarization and then an afterhyperpolarization
- The duration of the action potential is about 1-3 milliseconds, with an amplitude of about 100 mV.
- A strong stimulus causes a larger amplitude action potential as compared to one produced by a weak stimulus.
- At the peak of the action potential the membrane potential is about -40 mV.
- The afterhyperpolarization results primarily from increased pumping activity of the Na+/K+/ATPase.
The duration of the action potential is about 1-3 milliseconds, with an amplitude of about 100 mV.
At the neuromuscular junction, the motor nerve communicates with the skeletal muscle by releasing a chemical neurotransmitter. In regard to this neuromuscular transmission which ONE of the following typically occurs?
Select one:
- Binding of the neurotransmitter to the muscle receptor generates an inhibitory postsynaptic receptor potential (IPSP).
- A metabotropic receptor mediates a slow postsynaptic response to the neurotransmitter
- The neurotransmitter released by the nerve terminal is adrenaline.
- Acteylcholinesterase helps to terminate the response by metabolising the neurotransmitter.
- The neurotransmitter acts on gap junctions to cause a synchronized contraction.
Acteylcholinesterase helps to terminate the response by metabolising the neurotransmitter.
Which ONE of the following statements about ion channels is INCORRECT?
Select one:
- Ion channels have gates that may be opened by intracellular ligands.
- Ion channels allow transport of an ion against its electrochemical gradient.
- Ion channels allow transport of an ion against its chemical gradient, if the electrical driving force is sufficient.
- Ion channels can be opened either directly or indirectly by neurotransmitters.
- Ion channels may be opened by stretch of the cell membrane.
Ion channels allow transport of an ion against its electrochemical gradient.
This is the incorrect statement.
- Ion channels are passive (facilitated diffusion) transporters so that ions can only flow down their electrochemical gradients.
Choose the MOST CORRECT option. With regard to the ion channels underlying the action potential in a typical nerve axon:
Select one:
- Voltage-dependent K+ channels are open during the repolarization phase.
- Voltage-dependent K+ channels activate before the voltage-dependent Na+ channels.
- The voltage-dependent Na+ channels are inactivated when the action potential threshold is reached.
- Background or “leak” K+ channels are closed during the depolarization phase.
- Voltage-dependent K+ channels are closed during the afterhyperpolarization phase.
Voltage-dependent K+ channels are open during the repolarization phase.
Efflux of K+ through these open channels is what causes the repolarization.
The cell membrane is composed of a lipid bilayer with membrane proteins embedded within. In regards to the cell membrane, which ONE of the following statements is CORRECT?
Select one:
- Various membrane proteins dip into the lipid (or “anchor”) from either the intracellular or extracellular surface but typically do not transverse or span across the membrane as this would make the bilayer collapse.
- The membrane proteins and lipid molecules are fixed in a constant position, representing a mosaic pattern interspersed with cholesterol.
- The lipids within the cell membrane include phospholipids and sphingolipids
- The lipids that make up the membrane typically have a non-polar (hydrophobic) external surface and a polar (hydrophilic) interior.
- The lipid molecules require constant energy in the form of ATP to keep their hydrophobic regions closely adjacent in the bilayer arrangement.
The lipids within the cell membrane include phospholipids and sphingolipids
The schematic diagram below shows a model of epithelial transport in the kidney proximal tubule. The cell is at rest with typical ion concentrations in the extracellular and intracellular solutions. The membrane transport protein labelled “X”, which transports Na+, K+ and Cl- into the cell as shown, is an example of a:
Select one:
- Secondary active transporter (exchanger).
- Ion channel.
- Primary active transporter.
- Facilitated diffusion transporter.
- Secondary active transporter (co-transporter).
Secondary active transporter (co-transporter).
The transporter uses a Na+ gradient set up by active transport to transport K+ ions against their electrochemical gradient. Na+ and K+ are transported in the same direction (hence co-transport)
