GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Epigenetics

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Help With Epigenetics

Which of the following is an example of epigenetic inheritance?

Possible Answers:

Histone methylation patterns

Coding regions of genes

Purine dimers

Mismatch mutations

Correct answer:

Histone methylation patterns

Explanation:

Epigenetic inheritance is a term that describes heritable changes in gene expression that are not caused by DNA sequence. Purine dimers, mismatched bases, and the coding regions of genes are all describe information that is contained within the DNA sequence. Histone methylation patterns, however, are not contained within the DNA. This heritable information has various effects on gene expression that is not due to the sequence of DNA, thus making it an example of epigenetic inheritance. Expression patterns based on histone methylation affect the accessibility of a DNA sequence and the ability of RNA polymerase to bind the sequence for transcription, silencing a gene without actually altering it.

Example Question #2 : Help With Epigenetics

Commonly, _________ of histones leads to the silencing of genes.

Possible Answers:

phosphorylation

methylation

All of these would silence the gene

acetylation

Correct answer:

methylation

Explanation:

Out of the choices, only methylation of histones is commonly associated with the silencing of genes. Proteins known as histone methyltransferases bind a methyl group to amino acids in the histone, most commonly lysine or arginine. The result is a change in chromatin structure, most commonly blocking transcription sites and preventing expression.

Acetylation of histones is often found in activated genes. Phosphorylation of histones has been seen in DNA regulation, but it is unclear whether or not this modification affects the expression of genes.

Example Question #3 : Help With Epigenetics

Physical barriers between euchromatin and heterochromatin that often block enhancers from interacting with promoters, subsequently preventing transciption, are best characterized as  which of the following?

Possible Answers:

Nuclear lamins

Insulators

Mediators

Chromosomal looping

None of the other answers

Correct answer:

Insulators

Explanation:

The correct answer is insulators. Insulators are regions of DNA that serve as boundary elements, preventing the formation of euchromatin from heterochromatin. Mediators and chromosomal looping promote transcription factor recruitment to the DNA and promoter-enhancer interactions. Nuclear lamins provide structure to the nuclear envelope.

Example Question #4 : Help With Epigenetics

One mechanism by which the cell can stably alter gene transcription is through DNA _________, which will repress expression of the gene that is altered. This is an example of an epigenetic modification. 

Possible Answers:

phosphorylation

lipidation

carboxylation

acetylation

methylation

Correct answer:

methylation

Explanation:

Methylation is one of the most common epigenetic modifications that can be made to DNA sequences, and it typically results in repression of transcription at that site. This is typically achieved by modifying activity of the promoter region of a given gene. 

Example Question #5 : Help With Epigenetics

Which of the following best describes the mechanism by which histone acetylation results in increased transcription of a given chromosomal segment?

Possible Answers:

Acetylation removes methyl groups from the DNA sequence, thus relieving the repression that they induce on transcription. 

Acetylation activates transcription factors near the histone; this permits increased transcriptional activity at a given locus. 

Acetylation increases the interaction between the histones and the DNA strand; this conformation permits increased activation of polymerases. 

Acetylation reduces the interaction between the histones and the DNA strand; this relaxed conformation permits increased interaction with transcriptional machinery. 

Acetylation increases phosphorylation at crucial enhancer sites on the DNA sequence, thereby increasing transcription at those loci. 

Correct answer:

Acetylation reduces the interaction between the histones and the DNA strand; this relaxed conformation permits increased interaction with transcriptional machinery. 

Explanation:

Acetylation induces a change directly to the histone; the histone is typically positively charged and thus has a high level of interaction with the negatively charged DNA. Acetylation makes the histone less positive, and therefore it is less attracted to the DNA. This reduced interaction reduces the tight coiling of DNA around the histones, and transcriptional machinery has more access to the strand to increase transcription of genes at those sites. 

Example Question #6 : Help With Epigenetics

Histones are proteins that bind to and order the DNA into tight clusters, making it inaccessible to transcription machinery. How does the cells loosen the interaction of the histone and DNA.

Possible Answers:

By removing acyl groups from the histone

By methylating the DNA

By adding acetyl groups to the DNA

By adding methyl groups to the histone

By adding acetyl groups to the histone

Correct answer:

By adding acetyl groups to the histone

Explanation:

By adding acetyl groups to the positively charged histone tails, the cell can loosen the binding of DNA to a histone since DNA is largely negatively charged. This DNA can now be accessed by transcription machinery such as RNA polymerase. In this way acetylation of histones promotes transcription of genes on that piece of DNA. Deacetylation does the opposite - replaces positive charges onto histones so that they can interact more tightly with the DNA, ultimately suppressing expression of the DNA. 

Example Question #7 : Help With Epigenetics

Bees use enzymes called DNMT1 and DNMT3 (DNA methyltransferases) to create epigenetic changes that differentiate social castes at a common site pattern. What is this type of epigenetic change called?

Possible Answers:

Histone modification

ApT methylation

CpG methylation

Lysine acetylation

None of these are correct

Correct answer:

CpG methylation

Explanation:

CpG (cytosine-phosphate-guanine) methylation is a common type of epigenetic change caused by this set of enzymes. In this case, the bees use this to create difference castes of bees out of the same shared genome.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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