AP Biology : AP Biology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understanding Prokaryotic Genes

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

Possible Answers:

None of the other answers

Rho unwinds the DNA-RNA helix at the transcription bubble

Rho uses GTP as a source of energy

Rho is a nuclease that terminates transcription by cutting template DNA

Rho attaches to a Rho recognition site on the DNA template 

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 : Understanding Prokaryotic Genes

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

Possible Answers:

Clusters

Promoter sequences

Operator sequences

Linked genes

Operons

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 #11 : Genes And Dna

Bacterial plasmids can __________.

Possible Answers:

be present in multiple copies

carry antibiotic resistance genes

transfer between bacterial cells

All of these

integrate into the bacterial genome

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 #2 : Understanding Prokaryotic Genes

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

Possible Answers:

Restriction endonucleases

Viral vectors

Sanger sequencing

cDNA libraries

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 : Understanding Prokaryotic Genes

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 point mutation in the LacZ gene that abolishes enzyme activity

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

A frameshift mutation in the LacZ coding region

A mutation in the operator that blocks the activator from binding

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 #2 : Understanding Prokaryotic Genes

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

Possible Answers:

promoter

terminator

operator

gene

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 #11 : 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

Only eukaryotes perform translation

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

Eukaryotes perform translation before transcription, while prokaryotes perform transcription first

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.

Example Question #11 : Understand Regulation Of Transcription

Hydrogen bonds form between RNA nucleotide residues and DNA nucleotide residues, forming a temporary DNA-RNA hybrid. This process is a part of which phase of prokaryotic transcription?  

Possible Answers:

Template recognition

Initiation

Elongation

Termination

Correct answer:

Elongation

Explanation:

Prokaryotic transcription has three essential steps: initiation, elongation, and termination. The initiation process involves the binding of RNA polymerase to the correct region of DNA, and is characterized by the binding of the sigma factor to the RNA polymerase. Elongation occurs as the RNA strand is synthesized from the DNA template. Termination occurs when the RNA polymerase enzyme encounters a rho factor or particular DNA structure that causes it to release the DNA strand and cease RNA synthesis.

It is during the elongation process that RNA nucleotides are matched to the DNA template. The temporary DNA-RNA hybrid exists only briefly at the point of transcription before phosphodiester bonds form between adjacent ribonucleotides.

Example Question #12 : Understand Regulation Of Transcription

Which of these does not contribute to the termination of RNA transcription in bacteria?

Possible Answers:

Rho factor

Disruption of uracil-adenine RNA-DNA hybrid

Reattachment of the sigma factor

Hairpin loops

Correct answer:

Reattachment of the sigma factor

Explanation:

The sigma factor is an important part of initiation for prokaryotic transcription. Once transcription has been initiated, however, the sigma factor is released during elongation. RNA polymerase synthesizes the RNA product until it is interrupted in one of two ways. In rho-dependent termination, a rho factor protein interferes with RNA polymerase binding and causes it to release the DNA strand. In rho-independent termination, structural features of the DNA cause RNA polymerase to become detached. The structures include hairpin loops, which generate steric hindrance, and adenine-rich sequences, which lead to weak binding of the RNA product to the DNA template.

Example Question #13 : Understand Regulation Of Transcription

In prokaryotic transcription, which of the following is recruited to facilitate the binding of the synthesis enzyme to the DNA template?

Possible Answers:

A promoter sequence

The sigma factor

RNA polymerase

Messenger RNA

Correct answer:

The sigma factor

Explanation:

Inactive RNA polymerase must bind to a specific sigma factor in order to become active in gene transcription. Sigma factors are specialized transcription factors involved in recruiting and activating RNA polymerase. Only once RNA polymerase has bound the sigma factor can it identify promoter sequences and initiate transcription.

mRNA is the product of transcription and is not involved in prokaryotic RNA polymerase recruitment. An RNA primer is essential to recruiting DNA polymerase for DNA replication.

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