AP Biology : Understand regulation of transcription

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Transcription

What is the main difference between prokaryotic and eukaryotic genes?

Possible Answers:

Prokaryotes have one large gene, but eukaryotes have many smaller genes

Eukaryotes stores genes together in operons, but prokaryotes do not

Prokaryotic genes only have exons, but eukaryotic genes have exons and introns

Prokaryotic genes are not replicated, and only transcribed to RNA to then become protein

Prokaryotes do not have gene regulatory sequences, but eukaryotes do

Correct answer:

Prokaryotic genes only have exons, but eukaryotic genes have exons and introns

Explanation:

The correct answer is that prokaryotes only have exons, whereas eukaryotes have exons and introns. As a result, in eukaryotes, when mRNA is transcribed from DNA, the introns have to be cut out of the newly synthesized mRNA strand. The exons, or coding sequences, are then joined together. Prokaryotes do not have to process their mRNA to this extent. 

Example Question #1 : Understanding Prokaryotic Genes

A segment of prokaryotic DNA that binds transcription factors, usually as repressors that prevent transcription, are best known as __________.

Possible Answers:

Exons

Enhancers

Operators

Untranslated regions

Promoters

Correct answer:

Operators

Explanation:

The correct answer is operator. In most operons, repressors bind operators to prevent transcription of downstream genes.

Promoters are sequences of DNA upstream of genes that usually promote transcription by recruiting polymerases and other transcription factors. Enhancers are distant DNA sequences that promote transcription, whereas exons are the coding segments of a gene. 

Example Question #1 : Understand Regulation Of Transcription

What is the function of RNA polymerase in prokaryotes? 

Possible Answers:

None of the other answers 

Transcribe RNA from a DNA template

Replicate DNA during cell division

Translate RNA to protein

Repress transcription by binding operators

Correct answer:

Transcribe RNA from a DNA template

Explanation:

The correct answer is transcribe RNA from a DNA template. RNA polymerases are DNA-dependent, meaning that they require a DNA template; however, the new daughter strand that they create is composed of RNA. This RNA will then be translated into a functional protein by prokaryotic ribosomes. 

Example Question #3 : Understand Regulation Of Transcription

Which of the following is true of Rho-dependent transcription termination in prokaryotes?

Possible Answers:

Rho attaches to a Rho recognition site on the DNA template 

Rho is a nuclease that terminates transcription by cutting template DNA

Rho unwinds the DNA-RNA helix at the transcription bubble

Rho uses GTP as a source of energy

None of the other answers

Correct answer:

Rho unwinds the DNA-RNA helix at the transcription bubble

Explanation:

Rho attaches to a Rho recognition site on the mRNA strand and uses ATP to move along the mRNA strand towards RNA polymerase. When RNA polymerase pauses at the terminator, Rho unwinds the DNA-RNA hybrid. RNA polymerase, Rho, and the newly synthesized mRNA are released. 

Example Question #1 : Understand Regulation Of Transcription

Prokaryotic genes are often grouped together based on function. What are these groups of genes called?

Possible Answers:

Clusters

Operons

Linked genes

Promoter sequences

Operator sequences

Correct answer:

Operons

Explanation:

Bacteria organize some of their genes into operons. Operons contain genes of a similar function grouped together, and these genes are all transcribed together. For example, the lac operon involves the three genes required for breaking down lactose. There is no point in only transcribing one or two of the three genes since they are all required to break down lactose. Thus, they are under the control of a single operator and are all transcribed when the operator is active.

Example Question #1 : Understand Regulation Of Transcription

Bacterial plasmids can __________.

Possible Answers:

All of these

integrate into the bacterial genome

be present in multiple copies

transfer between bacterial cells

carry antibiotic resistance genes

Correct answer:

All of these

Explanation:

Plasmids are small pieces of DNA that are not part of a bacteria's genome. The genes contained on plasmids are not necessary for proper function of the bacteria. However, bacterial plasmids can carry genes to confer antibiotic resistance, and commonly do. Plasmids can be transferred between bacteria via conjugation, and can be integrated into their genomic DNA.. Plasmids are usually present in more than one copy per cell.

Example Question #1 : Understanding Prokaryotic Genes

Which of the following technological advances allows for the creation of a “recombinant plasmid”? 

Possible Answers:

cDNA libraries

Restriction endonucleases

Sanger sequencing

Viral vectors

Watson-Crick base pairing

Correct answer:

Restriction endonucleases

Explanation:

Restriction Endonucleases, or otherwise known as restriction enzymes, allows biologist to “cut and paste” different DNA sequences together. The use of restriction endonucleases is critical for the creation of recombinant plasmids. Viral vectors is incorrect, as viral vectors are useful in the application of recombinant DNA plasmids, delivery to host cell, but not in forming.

Example Question #1 : Understand Regulation Of Transcription

A mutation in the bacterial cell escherichia coli makes it unable to break down the sugar lactose. Which of the following is not a potential mutation that could result in this phenotype?

Possible Answers:

A frameshift mutation in the LacZ coding region

A mutation in the operator that blocks the activator from binding

A mutation in the region DNA polymerase binds to in the promoter

A point mutation in the LacZ gene that abolishes enzyme activity

Correct answer:

A mutation in the region DNA polymerase binds to in the promoter

Explanation:

DNA polymerase is not involved in the process of transcription. The incorrect answer could be corrected if it was rewritten as "a mutation in the promoter region where the RNA polymerase binds to."

Example Question #1 : Understanding Prokaryotic Genes

When a repressor binds to the __________, the LacZ gene does not get expressed. 

Possible Answers:

operator

gene

terminator

promoter

Correct answer:

operator

Explanation:

The region of a gene where activator/repressors bind in prokaryotic organisms is called an operator. The protein that's bound to the operon strongly influences the level of gene expression.

Example Question #9 : Understand Regulation Of Transcription

What is an important distinction between the process of translation in prokaryotes versus eukaryotes?

Possible Answers:

Prokaryotes produce a different set of amino acids from translation than eukaryotes

Eukaryotes perform translation before transcription, while prokaryotes perform transcription first

Only eukaryotes perform translation

Translation may occur at the same time as transcription in prokaryotes; they always occur separately in eukaryotes

Prokaryotes do not use RNA; eukaryotes do

Correct answer:

Translation may occur at the same time as transcription in prokaryotes; they always occur separately in eukaryotes

Explanation:

The lack of a nuclear membrane in prokaryotes has the advantage of allowing the cell to translate RNA as it is transcribed from DNA. This means that even before the full RNA is produced, the protein coded by that RNA can start being made. Eukaryotes produce RNA inside the nucleus, so it must first be fully transcribed and undergo modifications before it can be moved to the cytoplasm, where translation occurs.

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