Transcription Overview and Steps
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Questions and Answers

What is a key difference between transcription and replication?

  • Replication is selective to one gene.
  • Transcription does not require a primer. (correct)
  • Replication occurs in eukaryotic cells only.
  • Both processes synthesize RNA.

Which characteristic is unique to RNA polymerase compared to DNA polymerase?

  • RNA polymerase requires a primer.
  • RNA polymerase synthesizes DNA.
  • RNA polymerase has proofreading activity.
  • RNA polymerase has no exonuclease activity. (correct)

What type of modifications occur after transcription?

  • Only methylation occurs.
  • Post-transcriptional modifications are involved. (correct)
  • No modifications occur post-transcription.
  • All genes undergo replication modifications.

Which of the following is NOT a feature of RNA polymerase?

<p>Has proofreading activity. (B)</p> Signup and view all the answers

How does termination of transcription primarily occur?

<p>By recognizing a specific sequence on the transcript. (D)</p> Signup and view all the answers

What is the role of the Rho factor during RNA transcription termination?

<p>It serves as a helicase to facilitate RNA release from DNA. (C)</p> Signup and view all the answers

Which of the following correctly describes p-independent termination of transcription?

<p>It is characterized by the formation of a hairpin loop. (B)</p> Signup and view all the answers

During the initiation phase of transcription in prokaryotes, which component is essential for the binding of RNA polymerase to DNA?

<p>Sigma factor protein (A)</p> Signup and view all the answers

Which antibiotic inhibits RNA synthesis by binding to the β subunit of prokaryotic RNA polymerase?

<p>Rifampin (C)</p> Signup and view all the answers

What happens to the RNA transcript after it forms a hairpin loop during transcription termination?

<p>The RNA separates from the DNA template due to weak bonding. (B)</p> Signup and view all the answers

What is the primary action of RNA polymerase during the elongation phase of transcription?

<p>It adds RNA nucleotides complementary to the DNA template. (B)</p> Signup and view all the answers

In p-dependent termination, what specific sequence does the Rho factor recognize?

<p>C-rich rho recognition site (B)</p> Signup and view all the answers

What is the role of the TATA box in transcription initiation?

<p>It serves as the site of initial DNA melting. (B)</p> Signup and view all the answers

What is the purpose of the transcription bubble created during the initiation of transcription?

<p>To separate DNA strands for RNA synthesis. (D)</p> Signup and view all the answers

Where is the TTGACA box located in relation to the transcription start point?

<p>35 bases upstream of the start point (C)</p> Signup and view all the answers

Which statement accurately describes the process of transcription elongation?

<p>RNA polymerase moves along the DNA template strand in a processive manner. (A)</p> Signup and view all the answers

What initiates the elongation phase of transcription?

<p>The RNA transcript exceeding ten nucleotides in length (D)</p> Signup and view all the answers

What differentiates RNA polymerase from DNA polymerase during transcription?

<p>RNA polymerase can synthesize RNA without a primer. (A)</p> Signup and view all the answers

What is the primary outcome of reaching a termination signal during transcription?

<p>Synthesis of mRNA ceases and RNA polymerase detaches. (B)</p> Signup and view all the answers

Which factor is crucial for the RNA polymerase to recognize promoter sites?

<p>Sigma subunit (A)</p> Signup and view all the answers

What is the first nucleotide that is typically transcribed in the elongation phase?

<p>Adenine (A) (C)</p> Signup and view all the answers

What is the role of the template strand during transcription?

<p>It provides the sequence for the newly synthesized RNA transcript. (C)</p> Signup and view all the answers

Which of the following statements is true regarding RNA synthesis?

<p>Uracil replaces thymine in the RNA transcript. (D)</p> Signup and view all the answers

What are the three types of RNA found in prokaryotic and eukaryotic cells?

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

Which phase of transcription involves the addition of ribonucleotides to the growing RNA chain?

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

In eukaryotic genes, which of the following describes the role of introns?

<p>They are non-coding regions that are removed during RNA processing. (A)</p> Signup and view all the answers

What is the primary enzyme responsible for RNA synthesis during transcription?

<p>DNA-dependent RNA polymerase. (B)</p> Signup and view all the answers

What distinguishes the coding strand from the template strand?

<p>The coding strand has the same sequence as the RNA produced. (B)</p> Signup and view all the answers

Which base pairing relationships are correct during RNA synthesis?

<p>G pairs with C and A pairs with U. (C)</p> Signup and view all the answers

What is a primary reason eukaryotic transcription is more complex than prokaryotic transcription?

<p>Eukaryotic transcription relies on specific transcription factors. (B)</p> Signup and view all the answers

Which transcription factor is responsible for recognizing the TATA box in the promoter region?

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

What is the role of transcription factors in the transcription process of eukaryotes?

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

What is the typical location of the CAAT box in eukaryotic promoters?

<p>70 - 80 nucleotides upstream of the transcription start site. (B)</p> Signup and view all the answers

How does amanitin affect RNA polymerase II during transcription?

<p>It inhibits mRNA synthesis by binding tightly to RNA polymerase II. (D)</p> Signup and view all the answers

What is the significance of the GC box in eukaryotic promoters?

<p>It increases the frequency of transcription in genes that lack a TATA box. (A)</p> Signup and view all the answers

Which of the following statements about eukaryotic RNA polymerase II is true?

<p>It recognizes promoters through transcription factors. (D)</p> Signup and view all the answers

What differentiates eukaryotic transcription factors from prokaryotic mechanisms?

<p>Eukaryotic transcription factors are encoded by different genes and act as trans-acting factors. (B)</p> Signup and view all the answers

What role does TFII H play in the transcription process?

<p>It phosphorylates RNA polymerase and unwinds the DNA. (C)</p> Signup and view all the answers

During the elongation phase of transcription, the RNA polymerase synthesizes RNA in which precise direction?

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

What is the significance of the AAUAAA sequence in RNA transcription termination?

<p>It marks the cleavage and release site for the transcript. (D)</p> Signup and view all the answers

What modification occurs at the 5' end of eukaryotic mRNA?

<p>Attachment of a 7-methylguanosine cap. (A)</p> Signup and view all the answers

What distinguishes eukaryotic transcription from prokaryotic transcription?

<p>Transcription factors are critical in eukaryotic transcription. (A)</p> Signup and view all the answers

Which of the following statements about the removal of introns is correct?

<p>RNA splicing is necessary for processing eukaryotic mRNA. (B)</p> Signup and view all the answers

Which class of RNA is NOT directly produced by RNA polymerase during transcription?

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

What effect does actinomycin D have on RNA transcription?

<p>It inhibits RNA polymerase's movement along DNA. (A)</p> Signup and view all the answers

Flashcards

Transcription

The process of creating RNA from a DNA template.

Template Strand (DNA)

The DNA strand used as a pattern to create the RNA.

Coding Strand (DNA)

The DNA strand that is similar to the created RNA.

RNA Polymerase

Enzyme that builds RNA by following a DNA template.

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Gene

A segment of DNA that contains instructions for making a protein or RNA.

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Gene Expression

The process of using a gene's instructions to create a protein.

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Transcription Steps

Initiation, elongation, termination (in order).

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mRNA, rRNA, tRNA

Types of RNA involved in protein synthesis.

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Transcription Termination

The process of ending RNA synthesis, where RNA polymerase detaches from the DNA template.

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ρ-Independent Termination

A method of transcription termination that relies on a specific DNA sequence leading to the formation of a hairpin loop in the RNA, causing RNA polymerase to detach.

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ρ-Dependent Termination

A process where a protein called Rho (ρ) binds to the RNA and moves along it, eventually causing RNA polymerase to release from the DNA template.

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Palindromic Sequence

A DNA sequence that reads the same backward as forward, essential for ρ-independent termination.

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Rifampicin's Action

This antibiotic inhibits bacterial transcription by blocking RNA polymerase, preventing the formation of the first phosphodiester bond.

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Transcription Bubble

A localized unwinding of the DNA double helix caused by RNA polymerase during transcription.

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RNA Polymerase Holoenzyme

The fully active form of RNA polymerase in prokaryotes, composed of a core enzyme and the sigma factor.

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Sigma Factor

A protein subunit of RNA polymerase that helps identify and bind to promoter DNA sequences, initiating transcription.

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Pribnow box

A six-nucleotide sequence (TATAAT) located -10 bases upstream from the transcription start site. It's where DNA unwinding begins for transcription.

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TTGACA box

A sequence located -35 bases upstream from the transcription start site. It's where RNA polymerase initially binds to the DNA.

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Transcription Initiation

The first step of transcription, where RNA polymerase binds to the promoter region and begins unwinding the DNA.

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Transcription Elongation

The second stage of transcription, where RNA polymerase moves along the DNA template, reading it and adding nucleotides to the growing RNA molecule.

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Sigma Subunit

A protein subunit of RNA polymerase that helps recognize the promoter region and initiates transcription.

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Holoenzyme

The complete RNA polymerase enzyme, including the core enzyme and the sigma subunit.

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Eukaryotic Transcription

The process of creating RNA from DNA in eukaryotic cells, involving multiple transcription factors and RNA polymerases.

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Transcription Factors

Proteins that bind to DNA and regulate gene expression in eukaryotes. They help RNA polymerase find the right spot on DNA to start copying.

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CAAT Box

A DNA sequence (CCAATC) located upstream of the TATA box. It influences the frequency of transcription.

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GC Box

A DNA sequence rich in G and C bases. It replaces the TATA box in some genes and also influences transcription.

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TFII D

A transcription factor that binds to the TATA box, initiating the formation of a transcription complex.

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Amanitin's Effect

A toxin from poisonous mushrooms that inhibits RNA polymerase II, preventing mRNA synthesis and ultimately protein synthesis.

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Eukaryotic Transcription Complex

A complex formed by RNA polymerase II and transcription factors at the promoter region, initiating transcription.

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Replication vs. Transcription

Replication copies the entire DNA molecule into a new DNA molecule. Transcription creates a RNA copy from a DNA molecule, selected genes are copied, not the entire molecule.

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Primer Requirement

Replication requires a primer to start DNA synthesis, transcription does not need a primer.

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Polymerase Differences

DNA polymerase has proofreading ability to correct errors, RNA polymerase does not have this ability.

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TFII F's Role

TFII F brings RNA polymerase to the promoter, which is like the starting line for transcription.

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TFII H's Double Duty

TFII H acts as both a helicase, unwinding DNA, and a kinase, activating RNA polymerase.

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Transcription Starts Where?

Transcription begins at the starting point of a gene, which is like the signal to start reading.

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RNA Elongation Process

RNA polymerase moves along the DNA template, unwinding it and building a new RNA strand in the 5' to 3' direction.

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RNA Transcript Similarity

The RNA transcript's sequence is almost identical to the coding strand of DNA, except that thymine (T) is replaced with uracil (U).

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Termination Signal

The specific sequence AAUAAA on mRNA signals to stop transcription, ending the RNA creation process.

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Splicing Out Introns

Splicing is the process of removing non-coding sections (introns) from RNA, leaving only the important coding sections (exons).

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5' Cap Purpose

The 5' cap at the beginning of eukaryotic mRNA protects it from degradation and helps it bind to ribosomes for translation.

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Poly (A) Tail for Stability

The poly (A) tail, a string of adenine bases, is added to the end of mRNA to increase its stability and lifespan.

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Eukaryotic vs. Prokaryotic Transcription

Eukaryotic transcription is more complex, involving multiple polymerases and transcription factors, and occurs in the nucleus.

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Dactinomycin's Blocking Action

Dactinomycin, an anticancer drug, inhibits transcription by binding to the DNA template and interrupting RNA polymerase's movement.

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Study Notes

Transcription Overview

  • Transcription is the process of synthesizing RNA from a DNA template.
  • Specific DNA sequences (genes) are copied into RNA.
  • DNA-dependent RNA polymerase is the enzyme that catalyzes this process.
  • The process occurs in the cytoplasm of prokaryotes and in the nucleus of eukaryotes.

Steps in Transcription

  • Initiation: RNA polymerase binds to a specific DNA region, called a promoter. Promoter sequences, such as the TATA box (Pribnow box), are crucial in initiation. The promoter area helps select the start site of RNA synthesis. The RNA polymerase binds to the promoter and begins to unwind the DNA double helix.

  • Elongation: RNA polymerase moves along the template strand, adding RNA nucleotides complementary to the DNA template strand. The RNA is synthesized in the 5' to 3' direction, and uses nucleoside triphosphates as substrates.

  • Termination: RNA synthesis stops at a termination signal on the DNA template. This can occur spontaneously (intrinsic termination), or involve a protein factor called Rho (rho-dependent termination).

Prokaryotic Transcription

  • Prokaryotes have a single RNA polymerase that synthesizes all types of RNA.
  • The RNA polymerase is a holoenzyme complex, consisting of a core enzyme and a sigma factor.
  • The sigma factor is involved in promoter recognition. Specific promoter sequences, like -10 and -35 regions, in the promoter are important for sigma factor binding.
  • Termination signals cause the release of the RNA transcript.

Eukaryotic Transcription

  • Eukaryotes have three distinct RNA polymerases (I, II, and III) that synthesize different types of RNA.
  • RNA polymerase II is responsible for mRNA synthesis.
  • Transcription often involves numerous transcription factors. These factors act as regulatory proteins, helping determine which genes are transcribed.
  • Several specific sequences exist in the promoter region, unique to eukaryotes, such as the TATA box, CAAT box, and GC boxes, that the transcription factors bind to.
  • Common eukaryotic transcription factors include TFII A, B, D, E, F, and H.
  • Termination in eukaryotes is less simple than in prokaryotes, and occurs at specific signals.

Post-transcriptional Modifications

  • Eukaryotic RNA transcripts undergo significant modifications after transcription.
  • RNA splicing removes introns (non-coding regions) and joins exons (coding regions).
  • Capping occurs at the 5' end of the mRNA. A 7-methylguanosine cap protects the mRNA.
  • Polyadenylation adds a poly(A) tail to the 3' end of the mRNA. The poly(A) tail also protects the mRNA from degradation.

Inhibitors of Transcription

  • Some antibiotics, such as Rifampin, inhibit prokaryotic RNA polymerase activity by interfering with the formation of the first phosphodiester bond as well as the initial stage of the transcription process.
  • Amanitin, a toxin from poisonous mushrooms, inhibits eukaryotic RNA polymerase II.

Comparing Replication and Transcription

  • Replication involves copying the entire genome, while transcription copies only specific genes or groups of genes.
  • Transcription uses RNA polymerase, while replication uses DNA polymerase.
  • Transcription does not require a primer or proofreading, while replication does.
  • Transcription produces a single-stranded RNA molecule. Replication produces double-stranded DNA molecule.

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Description

This quiz covers the process of transcription, the synthesis of RNA from a DNA template. It details the steps involved including initiation, elongation, and termination, as well as the role of RNA polymerase. Perfect for biology students seeking to understand gene expression.

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