GRE Subject Test: Biology : GRE Subject Test: Biology

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

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Example Questions

Example Question #3 : Genetic Sequences, Transcription, And Translation

Some inherited diseases of the liver, including Wilson's Disease, are primarily or entirely genetically determined. Wilson's Disease results when a defect in a copper transporter in the small intestine occurs, leading to copper level disregulation in both the hepatocytes and the systemic circulatory system. Mutations have primarily been found in the copper transporter that helps load copper onto a transport protein, apoceruloplasmin, which normally creates serum-soluble ceruloplasmin with the addition of copper. Given this defect, serum studies of an individual with Wilson's Disease would likely show what kind of change in serum ceruloplasmin compared with a normal individual?

Possible Answers:

Decreased serum apoceruloplasmin

Decreased serum ceruloplasmin

Increased serum ceruloplasmin

The comparison cannot be estimated

Equivalent serum ceruloplasmin

Correct answer:

Decreased serum ceruloplasmin

Explanation:

The question informs us that the mutational defect in the gene involves the enzyme's ability to load copper onto apoceruloplasmin. Healthy individuals are able to load copper to apoceruloplasmin, creating serum-soluble ceruloplasmin. With this process disrupted in an individual with Wilson's Disease, we would expect that less ceruloplasmin would be produced because copper could not be transported. We would expect to see reduced serum levels of the complete protein, and high levels of copper building up in hepatocytes and circulatory serum.

Example Question #1 : Understanding Genetic Patterns

An error occurs during DNA replication, resulting in the insertion of a base pair. Replication of the original 3' DNA strand (template) produces a mutant 3' strand (mutant), as diagrammed below:

Template

3' - AUGGCCATTTTTATA - 5'

Mutant

3'- AUGCGCCATTTTTATA - 5'

Of the answers below, which best describes the type of mutation depicted above?

Possible Answers:

Duplication mutation

Nonsense mutation

Frameshift mutation

Repeat expansion

Missense mutation

Correct answer:

Frameshift mutation

Explanation:

The addition of a number of nucleotides that is not a multiple of three shifts the reading frame of the codons in the gene. One base pair was inserted early in the strand, thus shifting the codon reading frame +1 to the right.

Missense and nonsense mutations imply base pair substitutions, which did not occur in the diagram. Similarly, nothing was duplicated, and repeat expansion would require multiple repetitions of a short DNA sequence.

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 #1 : Understanding Transcription Factors

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

Possible Answers:

Transcription factors can only be activated by phosphatases.

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

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

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 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 #2 : 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

I and III

II, III, and IV

II and IV

I, III, and IV

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. 

Example Question #1 : Understanding Transcription

Which of the following are commonly found in a eukaryotic RNA-polymerase-II-dependent promoter?

I. Shine-Delgarno sequence

II. TATA element

III. Ribosomal binding site

Possible Answers:

I and III

I, II, and III

II only

I only

Correct answer:

II only

Explanation:

Of the three choices, the only element commonly found in a eukaryotic promoter is a TATA element. This is the site where TBP (TATA binding protein) binds and begins to recruit other transcriptional machinery.

The Shine-Delgarno sequence is commonly found on prokaryotic mRNA and serves as a ribosomal binding site. Because promoters are regions of DNA, both option I and II do not really apply.

Example Question #2 : Understanding Transcription

In eukaryotes, promoter sequences are regulatory elements found upstream of the transcription start site. Promoter sequences are required for transcription factors and RNA polymerase to recognize and bind to the DNA strand, thus promoting transcription of the genes on that strand and production of mRNA.

mRNA is ultimately translated into proteins, i.e. gene products. Consider a mutation in the promoter sequence that increases the affinity of RNA polymerase for the DNA strand. Compared to a sequence where the promoter sequence is wild-type, which of the outcomes below is most likely for this mutated promoter region?

Possible Answers:

The process described above has nothing to do with quantity of gene product

Overexpression of the gene product

20% reduction in gene product

Loss of the gene product

Altered tertiary structure of the gene product

Correct answer:

Overexpression of the gene product

Explanation:

The binding of RNA polymerase and transcription factors is tightly modulated by promoter elements. If affinity was increased compared to a wild-type sequence, we would expect that RNA polymerase would bind more easily to the sequence and produce more mRNA. Nothing about the nature of this mRNA is altered (since the coding sequences are unchanged); there is simply more of it, which would mean overexpression of the protein for which it codes.

Example Question #52 : Genetics, Dna, And Molecular Biology

What is the region of DNA where transcription factors and RNA polymerase bind, and that is also responsible for regulating transcription?

Possible Answers:

Insulator

Enhancer

Promoter

Intron 

Exon

Correct answer:

Promoter

Explanation:

The correct answer is promoter. The promoter is directly upstream of the start of transcription for a given gene. It is the site of transcription factor and RNA polymerase binding, and interacts with distant enhancers to regulate transcription. 

Example Question #53 : Genetics, Dna, And Molecular Biology

Eukaryotic transcription requires many proteins interacting in a coordinated fashion to drive the process of converting DNA to RNA. RNA polymerase, the enzyme that initiates transcription, needs a number of factors and components to being transcribing a gene. Which of the following answers is not one of these factors? 

Possible Answers:

DNA polymerase

Transcription factors

Core promoter sequence

Each of these are required for initiation of transcription

Activators

Correct answer:

DNA polymerase

Explanation:

DNA polymerase is a crucial factor required for replication of DNA, but is not a component utilized in the process of transcription. The core promoter sequence, activators, and transcription factors are all needed in order for RNA polymerase to begin the process. 

Example Question #1 : Understanding Translation

A protein that will be embedded in the plasma membrane is likely to be translated by __________

Possible Answers:

cytosolic ribosomes

ribosomes bound to the endoplasmic reticulum

nuclear ribosomes

ribosomes bound to the Golgi apparatus

Correct answer:

ribosomes bound to the endoplasmic reticulum

Explanation:

Most proteins that will be embedded in the plasma membrane are translated on ribosomes located in the rough endoplasmic reticulum. There are specific mechanisms and proteins that help insert the proteins into the membrane while they are being translated. Free-floating proteins are more likely to be translated in the cytosol. The nucleus and the Golgi do not have ribosomes used for translation, though the Golgi can play an important role in transporting proteins from the rough endoplasmic reticulum to the membrane.

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