Genetics : Regulation of Gene Expression in Prokaryotes and Eukaryotes

Study concepts, example questions & explanations for Genetics

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1

Example Question #1 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Which of the following describes a single genetic locus that controls more than one trait?

Possible Answers:

Polysomatic

Epistatic

Polygenic

Pleiotropic

Somatic

Correct answer:

Pleiotropic

Explanation:

The ability of a gene to affect an organism is multiple ways is called pleiotropy. During post-transcriptional modification, introns are removed from the mRNA sequence and exons are spliced together to create the desired protein product. By splicing the gene in different ways, different proteins can be produced, which will affect different traits.

Consider the sentence: The man ran on the track, but fell.

By splicing different portions of the sentence, it can take on different meanings: The man ran. The man on the track fell. The man fell. The man ran, but fell.

Where pleiotropic genes affect more than one trait, polygenic traits are affected by multiple genes. Epistatic genes are regulated by the activation of other genes.

Example Question #2 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

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

Possible Answers:

All of these would silence the gene

methylation

acetylation

phosphorylation

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 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Which of the following is the correct function of the eukaryotic enzyme analogous to DNA gyrase?

Possible Answers:

Prevent extreme supercoiling of the double helix

Catalyze the synthesis of an RNA primer

Recognize and bind to origins of replication

Ligate Okazaki fragments on the lagging strand
Correct answer:

Prevent extreme supercoiling of the double helix

Explanation:

Topoisomerases unwind supercoiling of DNA by breaking and rejoining DNA chains. 

Example Question #4 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Which DNA repair mechanism removes DNA damage caused by ultraviolet light? 

Possible Answers:

Mismatch repair

Direct repair

Base excision repair

Nucleotide excision repair

Correct answer:

Nucleotide excision repair

Explanation:

Nucleotide excision repair (NER) is used to repair thymine dimers, which are caused by ultraviolet damage. It also repairs bulky DNA adducts caused by carcinogens.

Example Question #3 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Which is a function of DNA polymerase III that occurs in the 3' to 5' direction of the template DNA strand?

Possible Answers:

Polymerization of the lagging strand

Removal of primers

Exonuclease proofreading

Polymerization of the leading strand

Correct answer:

Exonuclease proofreading

Explanation:

DNA polymerase III has these two functions:

1. 5'-3' polymerase requiring a 3' hydroxide primer and a DNA template

2. 3'-5' exonuclease proofreading

Both DNA polymerase I and DNA polymerase III are prokaryotic only. DNA polymerase I excises RNA primers with a 5' to 3' exonuclease.

Example Question #4 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

RNA primers are removed by which of the following exonucleases?

Possible Answers:

5'-3' DNA polymerase I

3'-5' DNA polymerase III

5'-3' DNA polymerase III

3'-5' DNA polymerase I

Correct answer:

5'-3' DNA polymerase I

Explanation:

5'-3' exonuclease removal of primers by DNA polymerase I.

DNA polymerase I is prokaryotic only, it degrades RNA primer and fills in the gap with DNA.

Example Question #7 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Glycosylases are required for which type of DNA repair?

Possible Answers:

Nucleotide excision repair

Direct repair

Mismatch repair

Base excision repair

Correct answer:

Base excision repair

Explanation:

Base excision repair (BER) requires glycosylases.

BER steps:

1. Glycosylases recognize incorrectly paired or damaged bases and 'flip' them out of the DNA chain without disrupting the phosphodiester backbone. The N-glycosidic bond of the flipped base is cleaved, leaving an AP site (site without a base).

2. AP site is removed by AP endonucleases and an AP lyase.

3. DNA polymerase I (prokaryotes) or DNA polymerase beta (humans) replaces the gap with a new base and DNA ligase seals the strand.

Example Question #8 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Which of the following is a DNA control element?

Possible Answers:

General transcription factors

Transcriptional repressors

TATA box

Transcriptional activators

Correct answer:

TATA box

Explanation:

DNA control elements are contained within the DNA helix.

DNA control elements:

1. TATA box: 25-35 basepairs (bps) upstream from start site, determines site of transcription and directs RNA polymerase II binding

2. Proximal promoter elements: 200 bps upstream of start and are roughly 20bps long

3. Enhancers are short regions of DNA that can be 50-1500bp long. They can be bound by activators to increase transcription. Can be far from the site of transcription and still be functional

NOT DNA control elements:

Transcription factors: bind to DNA control elements to influence transcription but are not considered control elements themselves.

Transcriptional repressors and activators: proteins coded by one gene that act to regulate transcription

Example Question #9 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

What type of chemical modification occurs when DNA is damaged by ultraviolet light?

Possible Answers:

Alkylation

Oxidation

Thymine dimerization

Depurination

Correct answer:

Thymine dimerization

Explanation:

Ultraviolet light causes thymine dimers in DNA. 

Example Question #10 : Regulation Of Gene Expression In Prokaryotes And Eukaryotes

Alternative splicing can result in which of the following?

Possible Answers:

Reversal of an exon

Duplication of an intron

Duplication of an exon

Removal of an exon

Correct answer:

Removal of an exon

Explanation:

Alternative splicing can:

1. Retain/remove exons.

2. Retain/remove introns.

3. Truncate/extend at 5' or 3' ends.

4. Have mutually exclusive exons (one or the other, but never both).

← Previous 1
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: