GRE Subject Test: Biology : Understanding Transcription Factors

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

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Example Questions

Example Question #1 : Understanding Transcription Factors

Consider the following scenario:

Gene-Z is a transcription factor required for transcribing the genes that contribute to populating the motor cortex with the proper number of neurons. Mutant mice for Gene-Z have 50% fewer motor neurons than controls (non-mutants). You genetically engineer a transgenic DNA construct that acts as a dominant negative to Gene-Z.

You transfect an embryonic mouse brain with this dominant negative and measure that all motor neurons get and expressed this construct. What would you expect the number of neurons in the transfected brain to be if the dominant negative works with 100% efficacy, and a normal motor cortex has 100,000 cells in the region you are examining?

Possible Answers:

Correct answer:

Explanation:

This question requires the knowledge that a dominant negative is expected to work in the same direction as a genetic mutant; it is a loss-of-function of the gene, by expressing a version of the gene that outcompetes the actual gene but cannot perform the proper biological process. Because we are assuming the dominant negative works perfectly, it should act just like the mutant and reduce cell number by 50%, giving us 50,000 cells. 

Example Question #2 : Understanding Transcription Factors

Which of the following statements about the function of transcription factors is not true?

Possible Answers:

Transcription factors can be activated by intracellular signaling cascades to modulate DNA expression in a context-dependent manner. 

Transcription factors can stabilize or destabilize the binding of RNA polymerases to DNA prior to transcription.

Transcription factors can bind to enhancer and promoter regions to upregulate DNA expression.

Transcription factors can only be activated by phosphatases.

Transcription factors can bind to enhancer and promoter regions to downregulate DNA expression.

Correct answer:

Transcription factors can only be activated by phosphatases.

Explanation:

Transcription factors can be activated or deactivated by any number of processes occurring within the cell and nucleus, and this it not limited to phosphatases (which remove phosphate groups from proteins). All of the other answers accurately describe possible activity and function of transcription factors.

Example Question #3 : Understanding Transcription Factors

Which of the following is true?

I. Transcription factors typically bind directly to the genes that they regulate.

II. Transcription factors can bind enhancer and promoter regions upstream of the genes they regulate. 

III. In eukaryotes, transcription factors frequently associate with coactivators.

IV. Transcription factors can either upregulate or downregulate transcription of a gene. 

Possible Answers:

II and III

II and IV

I, III, and IV

II, III, and IV

I and III

Correct answer:

II, III, and IV

Explanation:

Only the first statement in this question is false. Transcription factors typically (in fact, almost always) bind upstream of the gene to enhancer or promoter regions, and are rarely found interacting with the gene's coding region itself. 

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