Exam 11: Membrane Transport of Small Molecules and the Electrical Properties of Membranes

The permeability of a protein-free lipid bilayer to various molecules depends on their properties. Sort the following in order of low to high permeability from left to right. Your answer would be a six-digit number composed of digits 1 to 6, e.g. 123456. (A) O² (B) ATP (C) RNA oligonucleotide (D) Na⁺ (E) Glucose (F) Urea

Which of the following transporters mediates primary active transport when transporting the solutes in the directions indicated? The concentration of both solutes (shown as small circles and squares) is higher outside of the cell.

Sort the following events in a sequence that would lead to long-term potentiation (LTP). Your answer would be a five-digit number composed of numbers 1 to 5 only, e.g. 13245. (A) Activation of AMPA receptors (B) Glutamate release into the synaptic clefts (C) Activation of calcium-dependent protein kinases in the postsynaptic cell (D) Postsynaptic membrane depolarization (E) Activation of NMDA receptors

The nicotinic acetylcholine receptor is an ionotropic receptor that can be activated by nicotine, a stimulant drug found in cigarettes. Additionally, ?-bungarotoxin, a neurotoxin found in the venom of some snakes, binds preferentially and tightly to the closed conformation of the receptors. Another drug, donepezil, is a potent acetylcholinesterase inhibitor used to treat patients with Alzheimer's disease. If applied at a neuromuscular junction, indicate whether each of the compounds (1) acetylcholine, (2) nicotine, (3) ?-bungarotoxin, and (4) donepezil would enhance (E) or suppress (S) the Ca²⁺influx in the muscle cells. Your answer would be a four-letter string composed of letters E and S only, e.g. EESS.

For which of the following ions is the intracellular concentration typically higher than the extracellular concentration?

Which of the following transporters is NOT electrogenic?

Sanshool is a natural compound found in Sichuan pepper, which is commonly used in making spicy Asian food, and creates a numbing sensation in the mouth. It is known to inhibit a subset of potassium leak channels involved in maintaining the resting membrane potential in sensory neurons. How do you think sanshool affects these sensory neurons?

If the extracellular concentration of sodium ions is artificially decreased for a neuron, …

The membrane potential in a particular hyperpolarized cell is measured to be -70 mV. For each of the following channels in this cell, the calculated Nernst equilibrium potential for the corresponding ion is presented. Indicate whether each channel is driven to pass the ion into (I) or out of (O) the cell. Your answer would be a four-letter string composed of letters I and O only, e.g. IIII. ( ) K? channel; the K? equilibrium potential is -60 mV. ( ) Na? channel; the Na? equilibrium potential is +70 mV. ( ) Ca²? channel; the Ca²? equilibrium potential is +130 mV. ( ) Cl- channel; the Cl- equilibrium potential is -90 mV.

In neurons, the synaptotagmin-1 protein is localized to presynaptic axon terminals. When activated, it facilitates the fusion of neurotransmitter-containing synaptic vesicles to the plasma membrane, leading to neurotransmitter release into the synaptic cleft. Which of the following would you expect to directly activate synaptotagmin-1 for this function?

A membrane potential is plotted over time in the following graph. The Nernst equilibrium potentials for four ions (A to D) that affect the membrane potential in this system are indicated in the graph. What happened in the time period indicated by a question mark?

Why do cells not have membrane transport proteins for O₂?

Which of the following situations in a neuron results in action potentials that have extended depolarization phases?

Myelination of axons in the peripheral nervous system …

The lactose permease in Escherichia coli is an H⁺-lactose symporter that mediates the inward active transport of lactose if this sugar is present in the environment instead of glucose. Which of the following is true about this transporter?

MscS and MscL are mechanosensitive channels that ...

Which of the following graphs better represents the change in the relative conductance of Na⁺ and K⁺ channels during an action potential in a neuronal membrane?

Which of the following is the reason why an aquaporin does not pass ions (such as Na⁺) through?

Astroglial cells in the brain can actively import the amino acid glutamate from the synaptic cleft, convert it to the amino acid glutamine, and release the glutamine into the cleft to be subsequently taken up by the presynaptic neurons. The neurons then convert it back to glutamate. Why is this function of glial cells important?

Each single neuron acts as a computational device. Typically, the magnitude of the combined postsynaptic potential is encoded in the ... of firing of action potentials in the postsynaptic neuron.