AP Biology : Understanding Prokaryotic Differences

Study concepts, example questions & explanations for AP Biology

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Understanding Prokaryotic Differences

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

Possible Answers:

Only eukaryotes perform translation

Prokaryotes do not use RNA; eukaryotes do

Eukaryotes perform translation before transcription, while prokaryotes perform transcription first

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

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

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 #2 : Understanding Prokaryotic Differences

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:

Termination

Elongation

Template recognition

Initiation

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 #3 : Understanding Prokaryotic Differences

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

Possible Answers:

Rho factor

Hairpin loops

Reattachment of the sigma factor

Disruption of uracil-adenine RNA-DNA hybrid

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 #991 : Ap Biology

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

Possible Answers:

Messenger RNA

The sigma factor

A promoter sequence

RNA polymerase

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.

Example Question #4 : Understanding Prokaryotic Differences

Which of the following is not true about prokaryotic transcription?

Possible Answers:

Transcription occurs in the cytoplasm

mRNA is not subject to post-transcriptional modifications

RNA polymerase binds directly to the Shine-Delgarno sequence for some promoters

RNA polymerase interacts directly with the DNA

Correct answer:

RNA polymerase binds directly to the Shine-Delgarno sequence for some promoters

Explanation:

RNA polymerase does not interact with the Shine-Delgarno sequence. The Shine-Delgarno sequence is present on some prokaryotic mRNAs and serves as a ribosomal binding site for the initiation of translation. RNA polymerase is only involved in transcription and will bind to DNA, not RNA.

The other answers are all true and unique to prokaryotic transcription. Eukaryotic transcription is much more tightly regulated by transcription factors and DNA packaging (chromatin), and is confined to the nucleus.  

Example Question #5 : Understanding Prokaryotic Differences

Which of these are characteristic of transcription in eukaryotes? 

I.  Transcription can occur at the same time as translation

II.  The resulting RNA molecule is functionally mature

III.  The resulting RNA molecule must undergo splicing and other modifications before it is functional

IV.  Transcription occurs in the cytoplasm

Possible Answers:

I, II, and IV

I and III

I and IV

III only

II only

Correct answer:

III only

Explanation:

Prokaryotic transcription occurs in the cytosol, since prokaryotes lack a nucleus. This allows ribosomes to interact with RNA even while it is still be synthesized.

In contrast, eukaryotic transcription occurs in the nucleus. Once RNA has been synthesized it must be transported from the nucleus to the cytoplasm before it can interact with ribosomes. The newly-synthesized RNA undergoes splicing to remove introns, addition of a 5'-cap, and addition of a poly-A tail before it can exit the nucleus. These modifications help prevent degradation of the RNA. Only after these modifications can the RNA leave the nucleus and becomes functionally active.

Example Question #994 : Ap Biology

What is a Shine-Delgarno sequence?

Possible Answers:

A polymerase binding site in prokaryotic DNA

A site for restriction endonuclease digestion

A polymerase binding site in eukaryotic RNA primers

A ribosomal binding site in eukaryotic mRNA

A ribosomal binding site in prokaryotic mRNA

Correct answer:

A ribosomal binding site in prokaryotic mRNA

Explanation:

Shine-Delgarno sequences are ribosomal binding sites slightly upstream of start codons on prokaryotic mRNA. Eukaryotic mRNA is more complicated (it does not contain Shine-Delgarno sequences) and contains promoter regions that are responsible for recruiting translation factors and ribosomal subunits. 

Example Question #6 : Understanding Prokaryotic Differences

How does prokaryotic transcription differ from eukaryotic transcription?

Possible Answers:

Prokaryotic transcripts are polycistronic

Prokaryotic RNA polymerase transcribes the coding strand, rather than the template strand

Only prokaryotes use promoters

Prokaryotic transcripts are translated directly in the nucleus

Correct answer:

Prokaryotic transcripts are polycistronic

Explanation:

While prokaryotic and eukaryotic transcription processes are quite similar, there are some key differences. One significant difference is that prokaryotic transcripts can contain multiple genes, which will then transition as a single RNA strand to the ribosome. This is referred to as a polycistronic transcript. Eukaryotes have only one gene per transcript.

Both prokaryotes and eukaryotes use promoters. Prokaryotes do not have nuclei, though transcription and translation can occur simultaneously and in close proximity in these cells.

Example Question #7 : Understanding Prokaryotic Differences

In a bacterial cell, RNA polymerase binds to a promoter. What needs to bind to RNA polymerase for transcription to initiate?

Possible Answers:

A gamma factor

A metal cofactor

A prosthetic group

A sigma factor

An alpha factor

Correct answer:

A sigma factor

Explanation:

In bacterial cells, binding of a sigma factor to RNA polymerase is required for the initiation of transcription. Once the sigma factor binds, RNA polymerase is referred to as a holoenzyme and begins to make the RNA transcript.

Learning Tools by Varsity Tutors

Incompatible Browser

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