Question

Please help me with several of these questions, thank you very much.

1. During the propagation of an action potential along the axon of a neuron, what is

happening at the leading edge (the front) of the region of depolarization as it moves down

the axon?

a. Ligand-gated Na+channels are opening.

b. Voltage-gated Na+channels are opening.

c. Ligand-gated K+channels are opening.

d. Voltage-gated Na+channels have become inactive and refractory.

e. Voltage-gated Na+channels are closing.

2.

During transcellular transport of glucose across epithelial cells, how does glucose exit

the cell into the extracellular fluid?

a. by active transport in a Na+glucose symporter

b. by active transport in a Na+glucose antiporter

c. by active transport in a glucose uniporter

d. by passive transport in a glucose uniporter

e. by passive transport in a Na +glucose symporter

3. Chloride ion Cl- is close to equilibrium across the plasma membrane of many neurons.

What would happen to the membrane potential of a neuron if ligand-gated Cl- channels opened at the same time that the ligand-gated Na+channels opened?

a. There would be no effect of the Cl- channel opening and the membrane would depolarize normally.

b. The membrane potential would become more negative.

c. The depolarization would be suppressed and the membrane potential would depolarize less than normal.

d. The membrane potential would become more depolarized than normal.

4.

How is Ca 2+involved in the events at the neuromuscular junction when a signal from a neuron causes a muscle to contract?

a. Voltage-gated Ca2+channels open in the presynaptic neuron to cause the release of neurotransmitter into the synaptic cleft.

b. Voltage-gated Ca2+channels open in the muscle cell plasma membrane.

c. Ca2+ gated Ca2+release channels open in the sarcoplasmic reticulum.

d. Ca2+enters the muscle cell cytoplasm and causes muscle contraction.

e. all of the above

f. a and d only

5.

You are investigating the function of a membrane protein in epithelial cells and you

have labeled it with a fluorescent tag such as GFP. While observing it under the

fluorescence microscope, you carry out a FRAP (Fluorescence Recovery after

Photobleaching) experiment by bleaching a patch of your labeled proteins with a high-

powered laser and then watching what happens. What do you predict would happen if

your protein is a component of the tight junctions that are found between epithelial cells?

a. The fluorescence would not recover because the protein mobility is restricted.

b. The fluorescence would recover very quickly because fresh GFP-labelled proteins

would insert into the membrane from the cytosol.

c. The fluorescence would recover quickly because unbleached GFP-labelled proteins

would diffuse into the patch from surrounding membrane areas and replace the bleached

proteins.

d. The fluorescence would not recover because the lipid membrane is much less fluid in that region.

Answer 1

1. d.Voltage-gated Na+ channels have become inactive and refractory.

During Depolarisation,the membrane potential become less negative(more positive)

Depolarisation and hyperpolarisation occur only when ion channels in the membrane open or close

And also altered the ability of ions to enter or exit the cell

The positive flow of ions in a opened channels cause depolarization,i.e, opening of channels let Na+ ions into the cell

Two types of channels:

Ligand gated ion channels(the open and closing of channels determined by the binding of signaling molecules transmitters)

Voltage gated ion channels- Voltage across the membrane.

The following image  will explain detail about depolarisation:

The action potential travelled down the length of a neuron,and from axon hillock to the tip of the axon,with the receiving neuron, a synapse formed.

Initially, an action potential undergoes in one patch of membrane(right at the axon hillock).

So that Na+ ions rush into the cell through the patch.

These ions later spread inside the cell and depolarized the neighbouring patch of membrane

And also triggered the neighbouring membrane and caused the patch to undergo its own action potential.

Second, the action potential travelled in only one direction from the cell body to the axon terminal

Occuring because the patch of membrane undergone one action potential - Refractory period (nerve cell cannot respond to additional stimulation).

This refractory period occurs due to the inactivation of voltage gated sodium ions and failed to keep of potassium ions in closing

This occurs at the peak of action potential,the slow closure of potassium channels also contribute to the refractory period by makes it harder to depolarize the membrane

This refractory period clears that action potential can travel only forward down the axon,never backwards through the potion of axon where action potential undergone.

The action potential reaches the end of axon cause a neurotransmitter containing vesicles

It fused with the membrane and released these molecules into the synaptic cleft(space between neurons).

The neurotransmitter binds to the ligand gated channels and caused depolarization of that cell which undergo its own action potential.