High School Biology : Understanding Second Messenger Systems

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #11 : Transport And Signaling

What is the primary purpose of secondary messenger systems? In other words, what can a secondary messenger do in the body that a first messenger cannot?

Possible Answers:

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Secondary messengers help primary messengers cross the phospholipid bilayer by making them hydrophilic or hydrophobic.

None of these describe the unique role of secondary messengers.

Secondary messengers are able to bind to membranes, anchoring themselves in one place, whereas primary messengers float freely throughout the cell body and are unreliable.

Secondary messengers can take up extra space in a cell, thus limiting the ability of other chemical reactions to interfere with cell processes.

Correct answer:

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Explanation:

The primary ability of secondary messengers is their ability to leave the cell membrane and travel through the phospholipid bilayer by being selectively hydrophilic or -phobic, allowing egress. This enables, for example, a cascade effect that greatly amplifies the strength of the original primary messenger signal.

Example Question #2 : Understanding Second Messenger Systems

Which of the following is NOT an example of a second messenger molecule?

Possible Answers:

Cyclic AMP

Protein kinase C

Diacylglycerol

Cyclic GMP

Calcium

Correct answer:

Protein kinase C

Explanation:

All of the examples listed are considered second messengers except for protein kinase C, which interacts with second messenger pathways as an effector; however, it is not a second messenger itself.

Recall that second messengers are used to amplify signals within the cell. A ligand may bind to a receptor on the cell surface in order to activate a signaling cascade. Second messagers will help propagate this cascade throughout the cytosol. The messengers essentially help transfer the signal from the receptor on the cell membrane to the proteins in the cytosol that will ultimately be affected.

Example Question #12 : Transport And Signaling

Second messenger cascades can be triggered by the binding of an extracellular ligand to a membrane-spanning G-protein coupled receptor (GPCR).

Which of the following best describes what happens to the GPCR after a ligand has bound to it?

Possible Answers:

The GPCR is released from the membrane and enters the intracellular space to trigger downstream signaling cascades

The GPCR become inactivated

The GPCR undergoes a conformational change, making a binding site available for a G-protein within the cytosol

The GPCR remains unchanged, as no covalent modifications have been made

The GPCR opens to permit an influx of sodium ions (Na+)

Correct answer:

The GPCR undergoes a conformational change, making a binding site available for a G-protein within the cytosol

Explanation:

G-protein coupled receptors begin the signal transduction pathway by interacting with intracellular G-proteins. This interaction isn't possible until a ligand forces a conformational change in the GPCR, thereby freeing up a site for the G-protein to bind. This interaction permits the G-protein to exchange a GDP for a GTP, thereby activating the G-protein and continuing signal transduction.

Example Question #13 : Transport And Signaling

Which of the following is NOT a primary benefit of utilizing second messengers to transduce signals within a cell?

Possible Answers:

Second messengers can activate more than one pathway

Second messengers permit fine-tuned modulation of the signal through various intracellular enzymes

Second messengers eliminate the need for molecules to cross the semi-permeable membrane

Second messengers give cells direct access to extracellular material by permeabilizing the membrane

Second messengers permit amplification of the signal

Correct answer:

Second messengers give cells direct access to extracellular material by permeabilizing the membrane

Explanation:

The ligand binds the receptor on its extracellular terminus; therefore the ligand itself never enters the cell or passes through the membrane. Second messengers let the cell 'know' what is happening on the outside, but these extracellular molecules do not directly enter the cell.

All of the other answers describe benefits of the second messenger system. 

Example Question #1 : Understanding Second Messenger Systems

Which of the following is NOT an example of a second messenger?

Possible Answers:

IP3

Ca2+

cAMP

All of these are second messengers.

Epinephrine (adrenaline)

Correct answer:

Epinephrine (adrenaline)

Explanation:

Second messengers are intracellular signaling molecules. Epinephrine is a hormone that is released into the bloodstream and is thus never inside the cell. cAMP, Ca2+ and IP3 are all examples of second messengers. They respond to primary messengers—which are often hormones—by amplifying their effects and/or turning on downstream effectors.

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