E. coli Transcription Mechanisms

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What role does the sigma factor play in the function of RNA polymerase holoenzyme in E. coli transcription?

The sigma factor enables the RNA polymerase holoenzyme to recognize promoters and initiate RNA synthesis efficiently.

Describe the two steps involved in the binding of RNA polymerase holoenzyme to the promoter in E. coli.

First, the holoenzyme loosely binds to the -35 sequence, followed by a tight binding to the -10 sequence where it also unwinds about 17 bp of DNA.

What are the consensus sequences for the -35 and -10 regions of the common E. coli promoter?

The consensus for the -35 region is 5’-TTGACA-3’ and for the -10 region, it is 5’-TATAAT-3’.

Explain why variations in promoter sequences can affect transcription levels in E. coli.

<p>Promoters that deviate from consensus sequences can have different transcription levels based on sigma's recognition ability.</p> Signup and view all the answers

What constitutes the core enzyme of the RNA polymerase holoenzyme in E. coli?

<p>The core enzyme consists of four polypeptides: two α, one β, and one β’.</p> Signup and view all the answers

Why might E. coli produce different sigma factors in response to environmental changes?

<p>Different sigma factors allow E. coli to adapt its transcriptional response to changing conditions, regulating gene expression accordingly.</p> Signup and view all the answers

What is the main function of the terminator region in a gene's transcription process?

<p>The terminator region specifies where transcription will stop, ensuring proper termination of RNA synthesis.</p> Signup and view all the answers

How does the presence of the σ70 sigma factor influence the transcription of most E. coli genes?

<p>The σ70 sigma factor is typically the most abundant and enables transcription from σ70 promoters, facilitating efficient gene expression.</p> Signup and view all the answers

What are the three different RNA polymerases found in eukaryotes and their primary functions?

<p>RNA polymerase I transcribes rRNAs, RNA polymerase II transcribes mRNAs and some snRNAs, while RNA polymerase III transcribes tRNAs, 5S rRNA, and other snRNAs.</p> Signup and view all the answers

Why are eukaryotic RNA polymerases more challenging to study compared to prokaryotic RNA polymerases?

<p>Eukaryotic RNA polymerases are present at low concentrations, which makes them harder to isolate and study.</p> Signup and view all the answers

What is the role of core promoter elements in transcription?

<p>Core promoter elements specify where transcription starts and are located near the transcription start site.</p> Signup and view all the answers

What distinguishes promoter proximal elements from core promoter elements?

<p>Promoter proximal elements are located further upstream from the transcription start site and are crucial for high levels of transcription.</p> Signup and view all the answers

Identify the key activating proteins that interact with promoter proximal elements during transcription regulation.

<p>Activators are the key proteins that recognize and bind to promoter proximal elements to regulate transcription.</p> Signup and view all the answers

How do housekeeping genes relate to promoter proximal elements?

<p>Housekeeping genes feature common promoter proximal elements and are recognized by activator proteins common in all cell types.</p> Signup and view all the answers

Explain the significance of the TATA box in gene transcription.

<p>The TATA box assists in local DNA denaturation and sets the starting point for transcription at around -30.</p> Signup and view all the answers

What is the precursor to mature mRNA produced by RNA polymerase II during transcription?

<p>The precursor to mature mRNA is called pre-mRNA, which undergoes modifications to become mature mRNA.</p> Signup and view all the answers

What role do enhancers play in gene transcription?

<p>Enhancers are cis-acting elements that are required for maximal transcription of a gene by modulating transcription from considerable distances, sometimes thousands of base pairs away from the promoter.</p> Signup and view all the answers

How do general transcription factors (GTFs) contribute to transcription initiation?

<p>GTFs are essential for the assembly of the transcription initiation complex and facilitate the binding of RNA polymerase II to the core promoter.</p> Signup and view all the answers

How does the order of binding of GTFs and RNA polymerase II influence transcription initiation?

<p>The order of binding is important as it ensures the formation of a stable preinitiation complex, although the exact sequence in vivo remains less understood.</p> Signup and view all the answers

In what ways are eukaryotic transcription processes more complex than those in prokaryotes?

<p>Eukaryotic transcription involves more components, such as enhancers and GTFs, and is affected by nucleosome organization, making it slower and more flexible than prokaryotic transcription.</p> Signup and view all the answers

What is the significance of promoter proximal elements in gene expression?

<p>Promoter proximal elements are recognized by activator proteins specific to certain cell types or times, thereby influencing gene expression patterns.</p> Signup and view all the answers

Describe the involvement of activators in enhancer function.

<p>Activators bind to specific sequences within enhancers, facilitating the formation of protein complexes that bring enhancers close to the promoter to enhance transcription.</p> Signup and view all the answers

Why is the understanding of the binding sequence of GTFs important in transcription research?

<p>Understanding the binding sequence helps decipher the complexities of transcription initiation and how different factors interact to regulate gene expression.</p> Signup and view all the answers

What challenges arise from nucleosome organization during eukaryotic transcription?

<p>Nucleosome organization complicates transcription by obstructing access to DNA, which requires additional regulatory mechanisms and protein factors to facilitate transcription.</p> Signup and view all the answers

What are the three main regions of a prokaryotic gene involved in transcription?

<p>Promoter sequence, RNA-coding sequence, and terminator region.</p> Signup and view all the answers

Explain the significance of the Central Dogma as proposed by Francis Crick.

<p>The Central Dogma describes the flow of genetic information from DNA to RNA to protein.</p> Signup and view all the answers

How does RNA polymerase differ from DNA polymerase in initiation requirements?

<p>RNA polymerase does not require a primer to initiate synthesis, while DNA polymerase does.</p> Signup and view all the answers

What role does Uracil play in transcription compared to Thymine?

<p>Uracil is inserted in RNA instead of Thymine, which is used in DNA.</p> Signup and view all the answers

Describe the direction of RNA synthesis and DNA template reading during transcription.

<p>RNA is synthesized in a 5’-to-3’ direction while the DNA template is read in a 3’-to-5’ direction.</p> Signup and view all the answers

What types of RNA are produced during transcription and their respective functions?

<p>mRNA encodes polypeptides, tRNA brings amino acids to ribosomes, rRNA forms ribosomes, snRNA is involved in RNA processing.</p> Signup and view all the answers

Why is the process of elongation conserved between prokaryotes and eukaryotes?

<p>Elongation is highly conserved due to the fundamental nature of transcriptional mechanisms across life forms.</p> Signup and view all the answers

What is the role of gene regulatory elements in transcription?

<p>Gene regulatory elements help regulate the initiation and expression of transcription for specific genes.</p> Signup and view all the answers

What sequences does σ32 recognize and at which positions?

<p>σ32 recognizes CCCCC at -39 and TATAAATA at -15.</p> Signup and view all the answers

What are the five subtypes of eukaryotic RNA polymerases and their primary functions?

<p>RNAP I synthesizes rRNA, RNAP II synthesizes mRNA and snRNA, RNAP III synthesizes tRNA and rRNA, mitochondrial polymerase synthesizes mRNA, and chloroplast polymerase synthesizes cRNA.</p> Signup and view all the answers

Describe the role of the core enzyme during RNA synthesis after initiation.

<p>The core enzyme untwists the DNA helix and completes the RNA transcript once sigma factor is released.</p> Signup and view all the answers

How does the relative RNA content in eukaryotic cells compare among rRNA, tRNA, and mRNA?

<p>rRNA constitutes about 75% of the RNA content, tRNA about 15%, and mRNA makes up less than 10%.</p> Signup and view all the answers

What characteristic feature distinguishes rho-independent terminators from rho-dependent terminators?

<p>Rho-independent terminators have two-fold symmetry for hairpin loop formation, while rho-dependent ones often lack this symmetry.</p> Signup and view all the answers

Explain the proofreading mechanism employed by RNA polymerase during RNA synthesis.

<p>RNA polymerase uses a mechanism similar to DNA polymerase, removing newly inserted nucleotides by reversing the synthesis or cleaving RNA to resume forward synthesis.</p> Signup and view all the answers

Explain the significance of transcription factors in the context of eukaryotic transcription.

<p>Transcription factors are essential for RNA polymerase binding to the DNA, facilitating the transcription process.</p> Signup and view all the answers

What is the significance of the hairpin loop in rho-independent termination?

<p>The hairpin loop destabilizes the RNA-DNA hybrid, leading to termination of transcription.</p> Signup and view all the answers

What are the primary differences in the transcription process between eukaryotes and prokaryotes?

<p>Eukaryotic transcription is more complex, slower, and more flexible than prokaryotic transcription, involving multiple RNA polymerases and processing steps.</p> Signup and view all the answers

Describe the role of RNA polymerase II in eukaryotic transcription.

<p>RNA polymerase II is responsible for synthesizing mRNA and small nuclear RNA (snRNA) in the nucleoplasm.</p> Signup and view all the answers

How does σ54 respond to stress in comparison to other sigma factors like σ32?

<p>σ54 recognizes GTGGC at -26 and TTGCA at -14 and also arises in response to heat shock and other stresses.</p> Signup and view all the answers

What is the function of the ρ protein in rho-dependent termination?

<p>The ρ protein binds RNA and utilizes ATP hydrolysis to move along the transcript and destabilize the RNA-DNA hybrid.</p> Signup and view all the answers

How do the transcription processes differ between prokaryotes and eukaryotes?

<p>Prokaryotes have one RNA polymerase for all RNA types, while eukaryotes have three distinct polymerases for different RNA classes.</p> Signup and view all the answers

Flashcards

Transcription

The process of copying genetic information from DNA to RNA.

RNA polymerase

The enzyme that catalyzes the synthesis of RNA using a DNA template.

Promoter

A sequence of DNA that signals the start of transcription.

RNA-coding sequence

The region of DNA that contains the coding sequence for a gene.

Signup and view all the flashcards

Terminator

A sequence of DNA that signals the end of transcription.

Signup and view all the flashcards

Initiation of transcription

The first step in the transcription process, where RNA polymerase binds to the promoter and initiates RNA synthesis.

Signup and view all the flashcards

Elongation of transcription

The second step in transcription, where RNA polymerase elongates the RNA molecule using the DNA template.

Signup and view all the flashcards

Termination of transcription

The final step in transcription, where RNA polymerase releases the newly synthesized RNA molecule and detaches from the DNA template.

Signup and view all the flashcards

Sigma factor

A subunit of RNA polymerase responsible for recognizing and binding to specific promoter sequences, enabling initiation of transcription.

Signup and view all the flashcards

Start site (+1)

The location on a promoter DNA sequence where RNA polymerase initiates transcription.

Signup and view all the flashcards

Consensus sequences

The region on a promoter sequence (-35 and -10 bp upstream of the start site) where specific DNA sequences are recognized and bound by RNA polymerase.

Signup and view all the flashcards

Sigma factor regulation

The process in which different sigma factors, recognizing different promoter sequences, direct RNA polymerase to transcribe specific genes.

Signup and view all the flashcards

Sigma 32

A type of sigma factor that recognizes specific sequences in promoters and initiates transcription in response to heat shock and other stress conditions.

Signup and view all the flashcards

Sigma 54

A type of sigma factor that recognizes specific sequences in promoters and initiates transcription in response to heat shock and other stress conditions.

Signup and view all the flashcards

Sigma 23

A type of sigma factor that recognizes specific sequences in promoters and initiates transcription in phage T4-infected cells.

Signup and view all the flashcards

Transcription Elongation

The process of extending the RNA chain during transcription after the sigma factor has been released.

Signup and view all the flashcards

Terminator Sequence

A sequence of nucleotides that signals the end of transcription, allowing RNA polymerase to detach from DNA.

Signup and view all the flashcards

Rho-independent Terminator

A type of terminator sequence that does not require a specific protein to function. It relies on a hairpin loop and a poly(U) sequence.

Signup and view all the flashcards

Rho-dependent Terminator

A type of terminator sequence that requires the Rho protein to function. It lacks the poly(U) sequence and sometimes also the hairpin loop.

Signup and view all the flashcards

RNA polymerase II

RNA polymerase II transcribes messenger RNA (mRNA) which is used to make proteins - think of the 'II' as in 'protein production'.

Signup and view all the flashcards

RNA polymerase III

RNA polymerase III is responsible for transcribing transfer RNA (tRNA) and 5S rRNA. Think of the 'III' as in 'tRNA and 5S rRNA'.

Signup and view all the flashcards

Pre-mRNA

The initial transcript of protein-coding genes is called pre-mRNA. It undergoes further processing before becoming a mature mRNA.

Signup and view all the flashcards

Core Promoter Elements

The core promoter elements are located near the transcription start site and determine where transcription begins. The Inr is a pyrimidine-rich sequence spanning the start site.

Signup and view all the flashcards

TATA Box

The TATA box (or Goldberg-Hogness box) is a DNA sequence located -30 bases upstream from the start site. It helps unravel the DNA double helix, allowing the transcription machinery to access the gene.

Signup and view all the flashcards

Promoter Proximal Elements

Promoter proximal elements are located further upstream from the start site (-50 to -200) and enhance the rate of transcription.

Signup and view all the flashcards

Activator Proteins

Activator proteins bind to promoter proximal elements and enhance the transcription of genes.

Signup and view all the flashcards

rRNA (Ribosomal RNA)

The largest portion of RNA in a cell, accounting for about 75% of the total RNA. It is synthesized by RNA Polymerase I and plays a crucial role in protein synthesis.

Signup and view all the flashcards

Eukaryotic RNA Polymerases

RNA Polymerase I, II, and III are the primary RNA polymerases in eukaryotes, each responsible for synthesizing different types of RNA molecules. RNA Polymerase I makes rRNA, RNA Polymerase II makes mRNA and snRNA, and RNA Polymerase III makes tRNA and small rRNA.

Signup and view all the flashcards

mRNA Processing in Eukaryotes

Eukaryotic mRNA undergoes several processing steps before it can be translated into protein. This includes capping, splicing, and polyadenylation.

Signup and view all the flashcards

Eukaryotic Transcription vs. Prokaryotic Transcription

Eukaryotic transcription is a complex process, involving multiple proteins and steps. It is also slower and more flexible than prokaryotic transcription.

Signup and view all the flashcards

mtRNAP (Mitochondrial RNA Polymerase)

A specialized RNA polymerase found in mitochondria, responsible for transcribing mitochondrial DNA into mitochondrial mRNA.

Signup and view all the flashcards

Enhancers

DNA sequences that can be located at varying distances from the promoter and enhance transcription.

Signup and view all the flashcards

General Transcription Factors (GTFs)

A group of protein factors required for transcription initiation by all three RNA polymerases in eukaryotes.

Signup and view all the flashcards

Preinitiation Complex (PIC)

The fully assembled complex of RNA polymerase II and GTFs ready to initiate transcription.

Signup and view all the flashcards

In Vitro Transcription Initiation

The binding order of GTFs and RNA polymerase II to form the PIC in a test tube.

Signup and view all the flashcards

In Vivo Transcription Initiation

The less well-defined order of binding of GTFs and RNA polymerase II in a living cell.

Signup and view all the flashcards

Nucleosomes

Chromosomes in eukaryotes are organized into repeating units called...

Signup and view all the flashcards

Nucleosome Organization

Eukaryotic transcription is more complex than in prokaryotes because of...

Signup and view all the flashcards

Study Notes

Transcription in Prokaryotes and Eukaryotes

  • The central dogma outlines the flow of information: DNA → RNA → protein.
  • Transcription is the synthesis of RNA from a DNA template.
  • RNA polymerase is the enzyme that catalyzes transcription.
  • Prokaryotes have one type of RNA polymerase, while eukaryotes have three different types.
  • Eukaryotic RNA polymerase I creates ribosomal RNAs (rRNAs).
  • Eukaryotic RNA polymerase II creates messenger RNAs (mRNAs) and some small nuclear RNAs (snRNAs).
  • Eukaryotic RNA polymerase III creates transfer RNAs (tRNAs), 5S rRNA, and additional snRNAs.
  • Prokaryotic genes have three regions: promoter, RNA-coding sequence, and terminator.
  • A promoter sequence attracts RNA polymerase to initiate transcription.
  • The RNA-coding sequence specifies the RNA transcript.
  • A terminator region specifies the end of transcription.
  • E. coli promoters often have -35 and -10 consensus sequences, for efficient transcription.
  • Eukaryotic transcription initiation requires general transcription factors (GTFs) and RNA polymerase II binding to the core promoter.
  • Promoters in E. coli may deviate from consensus, affecting transcription levels.
  • RNA is transcribed in the 5' to 3' direction.
  • The template strand for transcription is read in the 3' to 5' direction.
  • Transcription initiation involves the RNA polymerase holoenzyme binding to the promoter.
  • Eukaryotic transcription is more complex than prokaryotic, slower, and more flexible.
  • Eukaryotic transcripts are processed before translation (e.g., removal of introns).
  • Eukaryotic RNA polymerase requires GTFs and has a more complex regulatory structure.

Transcription Process

  • Transcription is initiated by RNA polymerase binding to a promoter.
  • DNA unwinds locally, allowing RNA synthesis to begin.
  • RNA is synthesized using NTPs (not dNTPs) as precursors.
  • Uracil (U) substitutes for thymine (T).
  • RNA polymerase reads the template DNA strand in a 3' to 5' direction and produces RNA in a 5' to 3' direction.
  • Elongation is similar to DNA synthesis, but without a primer.
  • Transcription proceeds in the 5' → 3' direction, with nucleotides added to the 3' end of the growing RNA transcript.
  • Two types of termination sequences exist in prokaryotes: Rho-independent and Rho-dependent.
  • Rho-independent termination involves a hairpin loop structure to destabilize the RNA-DNA hybrid.

Promoter, RNA-coding Sequence, and Terminator Regions of a Gene

  • Promoters are DNA sequences that initiate transcription.
  • The RNA-coding sequence specifies which RNA will be produced.
  • The terminator sequence specifies the end of transcription.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

MB 6 Transcription in Prokaryotes and Eukaryotes PDF

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser