GRE Subject Test: Biology : Understanding Receptors

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Receptors

When presented with its ligand, glutamate, a metabotropic glutamate receptor (mGluR) can do any of the following except __________.

Possible Answers:

modulate transcription factor activation

change conformation to go from inactive to active

open to permit passage of sodium ions through the channel pore

activate the pathway that results in PKC activation

trigger an increase in intracellular calcium ion concentration

Correct answer:

open to permit passage of sodium ions through the channel pore

Explanation:

The key here is knowing that metabotropic receptors are NOT ion channels. They exert their effects through downstream signaling cascades. Ions cannot travel through a metabotropic receptor.

All other answers are potential outcomes of activating an mGluR.

Example Question #1 : Understanding Receptors

Once a G-protein coupled receptor (GPCR) has bound to its ligand, which of the following steps allows the  subunit to dissociate from the receptor and trigger downstream cascades?

Possible Answers:

Exchanging the G-protein's bound GDP for a GTP

Degradation of the GPCR's C-terminal tail that is bound to the  unit

None of these

Exchanging the G-protein's bound ADP for an ATP

Exchanging the G-protein's association with a magnesium ion for a calcium ion

Correct answer:

Exchanging the G-protein's bound GDP for a GTP

Explanation:

The G-proteins associated with the intracellular terminal of a GPCR dissociate when the change in conformation of the G-protein allows for a GTP to replace a GDP bound to the G-protein. ATP and ions are not at play here, nor is there degradation of the receptor's intracellular tail. It is the binding of GTP alone that triggers the cascading results of the protein's activation.

Example Question #2 : Understanding Receptors

Toll-like receptors (TLRs) are known for their role in innate immunity in humans and in many other organisms. How do these receptors induce downstream signaling to induce an innate immune response? 

Possible Answers:

Recognition of pathogen-associated molecular patterns (PAMPs)  

Recruitment of macrophages

Recognition and dimerization of integrins

Recognition of coagulation factors (platelet clotting factors)

Recruitment of natural killer cells

Correct answer:

Recognition of pathogen-associated molecular patterns (PAMPs)  

Explanation:

TLRs are transmembrane receptors that have an extracellular leucine-rich region that recognize PAMPs. Recognition of a pathogen factor causes the intracellular toll-interleukin-1 domain to bind adaptor proteins to induce expression of genes responsible for initiating an innate immune response. 

Example Question #3 : Understanding Receptors

Paracrine signaling refers to which type of cell signaling?

Possible Answers:

Same cell signaling

Long range cell signaling

Intracellular signaling

Close range cell signaling 

Cell signaling across a synapse

Correct answer:

Close range cell signaling 

Explanation:

Paracrine signaling refers to close range cell to cell signaling. This is different from endocrine signaling in which signaling molecules (hormones) are released into the blood stream in order to communicate with distant cells.

Autocrine signaling is a type of signaling in where the signaling molecule and the receptor for that messenger are found on the same cell. Cell signaling across a synapse is called synaptic signaling. 

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