Cell Signalling Pathways Questions and Answers

Answer: A

Pumps hold cytosolic calcium about ten thousand times below the level outside and in the endoplasmic reticulum, so opening a channel produces a sharp and unmistakable rise. Restoring the low resting level afterwards costs the cell energy.

Answer: B

Produced when a membrane lipid is cleaved, it diffuses to the reticulum and opens calcium channels there. The other product of that cleavage, diacylglycerol, stays in the membrane and activates protein kinase C. One cleavage event thus produces two distinct signals at once.

Answer: C

The first two are correct. The third misplaces their role, since the receptor carries the message across the membrane and the second messenger then spreads it within the cell. The two roles are sequential rather than interchangeable.

Answer: D

It diffuses through membranes directly and acts on an enzyme inside the target cell, relaxing smooth muscle in blood vessels. Its very short life limits its action to the immediate neighbourhood. Nitroglycerin relieves angina by releasing it in the vessel wall.

Answer: A

Correct answer: the shape of its binding site

Specificity is molecular complementarity: the binding site’s shape and its distribution of charge and hydrogen-bonding groups fit one molecule and not others. That is why a cell is deaf to every signal for which it lacks a receptor, however concentrated, and why a drug designed to fit the same site can mimic or block the natural ligand.

Answer: B

Occupying the site blocks the natural signal from binding, so the pathway is silenced. Beta blockers work this way on the receptors that adrenaline would otherwise activate. An agonist would do the opposite and stimulate the receptor.

Answer: C

Correct answer: True

An agonist binds the receptor and produces the same conformational change as the natural ligand, so it triggers the response - morphine at the opioid receptor. An antagonist binds without activating and so occupies the site, preventing the natural ligand from acting - a beta blocker at the adrenergic receptor. Both depend on fitting the same binding site, and they differ only in what happens after binding.

Answer: D

Both are true and the reason gives the mechanism: with the receptors blocked, circulating adrenaline cannot exert its usual stimulating effect, so the heart is left responding to a weaker signal than it otherwise would.

Answer: A

Vesicles carrying the transporter fuse with the surface, so glucose enters more rapidly. Withdrawing the signal causes the transporters to be retrieved again. The response is therefore quick to establish and quick to reverse.

Answer: B

The signal is present but the cells respond poorly, which is a failure of signal reception rather than of production. Type 1 diabetes, by contrast, is a failure to make the hormone at all. The two conditions share a name and a symptom but not a cause.