GABA receptors play an essential role in neurotransmission in the central nervous system. In response to the appropriate signal, these receptors open up and allow Cl- to flow into the cell. Given this information, GABA receptors can be classified as a

Question

A.  gated ion channel.
B.  gated carrier protein.
C.  symporter.
D.  Cl- pump.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you know about protein transporters? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  gated ion channel.

Clarify Question
· What is the key concept addressed by the question?
        o The question asks about the transport of molecules across a membrane.
· What type of thinking is required?
        o You are being asked to apply your knowledge of transport proteins to explain how Cl- ions cross a membrane.
· What key words does the question contain and what do they mean?
        o GABA receptors – these are proteins in a membrane that bind to aligand, in this case the neurotransmitter GABA.
        o Open up and allow Cl- into a cell – the GABA receptors are normally closed and when the open Cl- can cross the membrane.
        o Cl- - this is a chloride ion with a negative charge.

Gather Content
· What do you know about protein transporters? How does it relate to the question?
        o Charged and polar molecules cannot cross a membrane without the assistance of a protein channel. GABA receptors can bind aligand (GABA) and then open up a channel that allows Cl- ions to move through. In this way the GABA receptor is acting as a gate that can open to allow ions to flow through, down their concentration gradient.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Symporters open channels that allow two molecules to enter a cell simultaneously. One of the molecules is flowing down its concentration gradient and that energy is used to move the second molecule against its concentration gradient. In the case of the GABA receptor, no mention is made of a second molecule moving through the channel.
        o A pump is a protein that uses ATP or another energy source to drive active transport of a molecule against its concentration gradient. No mention is made of ATP being used in the case of the GABA receptor.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The best answer is that the GABA receptor is a gated ion channel. When it is closed, no ions can move across the channel. When GABA binds to the receptor, the channel opens and the Cl- ion can move down its concentration gradient and enter the neuron.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply the definition of a gated ion channel to a specific example. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you understand that Cl- was an ion? Did you recognize that the GABA receptor was acting as a gate, preventing Cl- ions from crossing the membrane until GABA bound to the receptor? Did you observe that no mention was made of ATP or another molecule moving across the membrane?