The lactose analog isopropyl-beta-D-thio-galactoside (IPTG) is often used to regulate gene expression systems in bacteria. IPTG does not act as a substrate for beta-galactosidase, but can bind to, and inactivate, the repressor. In this case, IPTG serves as a(n)

Question

A.  inducer.
B.  repressor.
C.  DNA-binding protein.
D.  operon.

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 already know about prokaryotic transcriptional regulation?

Consider Possibilities
· Consider the different answer options. Which can you rule out?
 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.  inducer.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses prokaryotic transcriptional regulation.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
· What key words does the question contain and what do they mean?
        o Beta-galactosidase is an enzyme that processes lactose.
        o A lactose analog is a small molecule very similar to lactose. Lactose is a disaccharide— that is, a two-ring sugar.
        o A substrate is a molecule that an enzyme acts upon, usually changing it to another molecule.

Gather Content
· What do you already know about prokaryotic transcriptional regulation?
        o We have seen several examples of prokaryotic transcriptional regulation.
        o For instance, we learned that the lac operon is activated in the presence of lactose. Lactose binds to the repressor protein, blocking it from preventing transcription. In this way, lactose “induces” transcription.

Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Can we call the IPTG in this case a repressor? No, because its role is to activate transcription. (This is true even if it technically acts by repressing a repressor.)
        o Can we call the IPTG in this case an operon? No, an operon is a set of genes in the DNA, under coordinated transcriptional control. The IPTG is a small sugar, not DNA.
        o Can we call the IPTG in this case a DNA-binding protein? No, because the IPTG is a sugar, not a protein. Also it does not directly bind the DNA – it binds to the DNA-binding repressor protein as a cofactor.
 Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o When a small molecule induces gene expression by interacting as a cofactor with a protein, we can call the molecule an “inducer”.

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 what term you would use to describe IPTG when it acts to turn on gene expression.
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that IPTG binds to a regulatory protein to activate gene expression?
        o Did you remember that that type of molecule is called an inducer?