Transcription Processes
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Questions and Answers

What distinguishes RNA polymerases from DNA polymerases in their ability to initiate polynucleotide synthesis?

  • Both RNA and DNA polymerases require a primer for polynucleotide synthesis.
  • RNA polymerases require a pre-existing primer to begin synthesis, whereas DNA polymerases can start from scratch.
  • Neither RNA nor DNA polymerases require a primer for polynucleotide synthesis.
  • DNA polymerases require a pre-existing primer to begin synthesis, whereas RNA polymerases can start from scratch. (correct)

A mutation occurs in the terminator sequence of a bacterial gene. What is the most likely consequence of this mutation?

  • Transcription will terminate prematurely.
  • The rate of elongation during transcription will decrease.
  • RNA polymerase will fail to bind to the promoter.
  • Transcription will continue past the normal termination point. (correct)

In molecular biology, what do the terms 'upstream' and 'downstream' refer to?

  • They indicate the relative position of nucleotide sequences with respect to the direction of transcription. (correct)
  • They determine the stability of the mRNA molecule after transcription.
  • They define the speed at which RNA polymerase moves along the DNA template.
  • They describe whether the DNA sequence is located on the leading or lagging strand.

If a researcher identifies a new bacterial RNA polymerase, what RNAs would it most likely synthesize?

<p>mRNA, tRNA, and rRNA. (B)</p> Signup and view all the answers

Which of the following is NOT a stage of transcription?

<p>Replication (B)</p> Signup and view all the answers

A certain segment of DNA is transcribed into RNA. Which strand serves as the template?

<p>The template strand (A)</p> Signup and view all the answers

In eukaryotes, which RNA polymerase is responsible for transcribing pre-mRNA?

<p>RNA polymerase II (A)</p> Signup and view all the answers

Which of the following is the correct order of events in transcription?

<p>Initiation -&gt; Elongation -&gt; Termination (B)</p> Signup and view all the answers

What role do transcription factors play in eukaryotic transcription initiation?

<p>They recognize and bind to the promoter, facilitating RNA polymerase II binding. (B)</p> Signup and view all the answers

What is the primary role of transcription factors in eukaryotic transcription?

<p>To guide and facilitate the binding of RNA polymerase to the promoter. (A)</p> Signup and view all the answers

During transcription elongation, in which direction is the RNA transcript synthesized?

<p>5' → 3' (C)</p> Signup and view all the answers

A mutation occurs in the TATA box of a eukaryotic promoter. What is the most likely consequence?

<p>Transcription factor binding will be disrupted, reducing transcription. (C)</p> Signup and view all the answers

During transcription elongation, what prevents the synthesized RNA molecule from continuously binding to the DNA template?

<p>The newly synthesized RNA molecule peels away from the DNA template as the DNA double helix reforms. (B)</p> Signup and view all the answers

What is the primary difference in how bacterial and eukaryotic cells handle the RNA transcript immediately after transcription?

<p>Bacterial transcripts can be immediately used as mRNA; eukaryotic transcripts need processing. (B)</p> Signup and view all the answers

In bacterial transcription termination, what directly causes the RNA polymerase to detach from the DNA and release the transcript?

<p>A terminator sequence in the transcribed RNA functions as the termination signal. (C)</p> Signup and view all the answers

Which of the following components is NOT directly involved in the initiation of transcription in eukaryotes?

<p>Ribosomes (D)</p> Signup and view all the answers

How does the process of transcription termination differ between bacteria and eukaryotes?

<p>Bacteria use a terminator sequence, while eukaryotes use a polyadenylation signal sequence. (C)</p> Signup and view all the answers

What is the immediate consequence of RNA polymerase II transcribing the polyadenylation signal sequence (AAUAAA) in eukaryotes?

<p>Proteins bind to the signal, cleaving the RNA transcript and releasing pre-mRNA. (C)</p> Signup and view all the answers

During transcription, what is the role of the non-template strand of DNA?

<p>It is not directly involved in transcription. (D)</p> Signup and view all the answers

Which event signals the termination of transcription?

<p>A specific sequence causing the polymerase to detach. (B)</p> Signup and view all the answers

If X-rays induce DNA sequence changes in the TATA box of a gene's promoter, how would this affect the process of transcription?

<p>It would disrupt the binding of transcription factors, affecting the initiation of transcription. (D)</p> Signup and view all the answers

During the elongation of the RNA strand, approximately how many DNA nucleotides are exposed at a time for pairing with RNA nucleotides?

<p>10-20 (B)</p> Signup and view all the answers

How does the binding of RNA polymerase to the promoter influence the process of transcription?

<p>It determines the start point and direction of transcription. (A)</p> Signup and view all the answers

Following cleavage of the pre-mRNA from the polymerase after transcription of the polyadenylation signal sequence in eukaryotes, what happens to the remaining RNA being transcribed by RNA polymerase II?

<p>It is degraded by enzymes starting at the 5' end until the polymerase dissociates from the DNA. (E)</p> Signup and view all the answers

Flashcards

Promoter Sequence

DNA region that initiates transcription by binding RNA polymerase.

Transcription Initiation Complex

The complex formed when RNA polymerase and transcription factors bind to the promoter.

RNA Polymerase II

Enzyme responsible for synthesizing mRNA from a DNA template in eukaryotes.

Transcription Elongation

The process where RNA polymerase adds RNA nucleotides to the growing RNA strand.

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Termination of Transcription

The process by which RNA polymerase ceases transcription and releases the RNA transcript.

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Polyadenylation Signal Sequence

A specific DNA sequence (AAUAAA) that signals for the termination and processing of eukaryotic pre-mRNA.

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Transcription Factors

Proteins that assist RNA polymerase in binding to the promoter in eukaryotes.

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TATA Box

A DNA sequence in the promoter that is crucial for the binding of transcription factors.

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RNA Polymerase

Enzyme that synthesizes RNA from a DNA template during transcription.

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Eukaryotic Promoter

Contains a TATA box and is involved in the initiation of transcription in eukaryotes.

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Initiation of Transcription

The first step of transcription where RNA polymerase binds to the promoter and unwinds DNA.

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Elongation

Process where RNA polymerase moves along DNA, synthesizing RNA by adding nucleotides.

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Messenger RNA

RNA that carries information from DNA to ribosomes for protein synthesis.

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Transcription Unit

The DNA segment that is transcribed into an RNA molecule.

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Promoter

DNA sequence that signals where transcription begins by binding RNA polymerase.

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Terminator Sequence

DNA sequence that signals the end of transcription.

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Downstream

The direction in which RNA polymerase synthesizes RNA during transcription.

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Upstream

The direction opposite to where transcription occurs, referring to sequences before the transcription start site.

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Pre-mRNA

The initial RNA transcript processed to become mature mRNA in eukaryotes.

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Study Notes

RNA Polymerase Binding and Initiation

  • The promoter sequence of a gene includes within it the transcription start point—the nucleotide where RNA polymerase begins synthesizing mRNA—and typically extends several dozen or so nucleotides upstream from the start point (Figure 17.9). Based on interactions with proteins (transcription factors), RNA polymerase binds in a precise location where transcription starts. This binding determines which orientation on the promoter it will travel.

Stages of Transcription Initiation

  • The stages of transcription—initiation, elongation, and termination—apply to both bacteria and eukaryotes, but details of the RNA transcript, as described in the text, also apply to bacteria, the RNA transcript is immediately usable as mRNA
  • Figure details stages of transcription initiation in bacteria
  • Initiation: RNA polymerase binds to the promoter, the polymerase unwinds the DNA strands and initiates the synthesis of the RNA template strand.
  • Elongation: The polymerase moves along the unwinding DNA and elongating the strand. The DNA double helix re-forms.
  • Termination: The RNA polymerase detaches from the DNA.
  • Eukaryotic promoter
  • Eukaryotic promoters contain a core promoter, which includes a TATA box (a DNA sequence) located upstream of the transcriptional start site.
  • Transcription factors bind to the TATA box and help the RNA polymerase II bind to the promoter.
  • Additional transcription factors bind to the RNA polymerase II.

RNA Polymerase II

  • Figure 17.9 depicts the initiation of transcription at a eukaryotic promoter. In eukaryotic cells, protein called transcription factors mediate the initiation of transcription by RNA polymerase II.

Elongation of the RNA Strand

  • As RNA polymerase moves along the DNA, it unwinds the DNA helix, exposing about 10–20 DNA nucleotides at a time for pairing with RNA nucleotides (Figure 17.10). The enzyme adds nucleotides to the 3' end of the growing RNA molecule as it moves along the synthesized RNA molecule behind the polymerase. The DNA double helix reforms from its DNA template, and the RNA polymerase peels away. Transcription progresses at a rate of about 40 nucleotides per second in eukaryotes.
  • A single gene can be transcribed simultaneously by several RNA polymerase.

Termination of Transcription

  • Bacteria and eukaryotes differ in the way they terminate transcription. In bacteria, transcription proceeds through a terminator sequence in the DNA. The transcribed terminator sequence, (transcription termination signal), causes the polymerase to detach from the DNA and release before transcription. In eukaryotes, no further modification occurs.

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Description

Explore the complexities of transcription in both prokaryotes and eukaryotes. Topics include RNA vs. DNA polymerases, mutation consequences, transcription factors and RNA synthesis.

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