Bacterial Genes and Transcription

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Questions and Answers

What is the primary role of RNA polymerase in bacterial transcription?

To synthesize RNA from the DNA template (correct)

To build cellular structures

To separate double-stranded DNA

To regulate gene expression

Which of the following best describes a gene?

A cellular structure providing genetic information

A sequence of RNA that regulates cellular activities

A segment of DNA coding for a functional RNA or protein (correct)

A protein that catalyzes metabolic reactions

During the process of transcription, which step involves creating a template from the DNA?

Proteins catalyzing RNA synthesis

Synthesis of cellular structures

Regulation of gene expression

Separation of double-stranded DNA (correct)

What is the result of transcription in bacterial cells?

The copying of DNA to produce RNA Signup and view all the answers

Which component is NOT part of a gene as defined in the content?

Nucleotide sequences for cellular signaling Signup and view all the answers

What is the consensus sequence for the -10 element in bacterial promoters?

TATAAT Signup and view all the answers

Which nucleotide is most commonly found at the first position of the -10 element in bacterial promoters?

T Signup and view all the answers

What is the significance of the relative positions of the -10 and -35 elements?

They indicate the direction RNA polymerase should move. Signup and view all the answers

In which direction does RNA polymerase synthesize RNA during transcription?

5' to 3' Signup and view all the answers

What is the role of the bottom DNA strand in the transcription process?

It serves as the template for RNA synthesis. Signup and view all the answers

Which base is replaced by uracil in the newly synthesized RNA?

Thymine Signup and view all the answers

What percentage of -10 promoters have an 'A' in the fourth position?

56% Signup and view all the answers

What represents the transcription start site in the schematic provided?

+1 position Signup and view all the answers

Which sequence represents the consensus -35 element in bacterial promoters?

TTGACA Signup and view all the answers

What should you learn regarding the -10 and -35 elements in bacterial promoters?

Relative locations and exact sequences. Signup and view all the answers

What sequence structure is formed during Rho-independent transcription termination?

A hairpin loop Signup and view all the answers

What component is primarily responsible for Rho-dependent transcription termination?

Rho protein Signup and view all the answers

Which region of the RNA structure has weaker hydrogen bonds to the DNA template in Rho-independent termination?

U-rich region Signup and view all the answers

How does the Rho protein move towards the RNA polymerase?

By hydrolyzing ATP Signup and view all the answers

What is the function of the Rho Utilization Site (RUT)?

Guide Rho protein binding Signup and view all the answers

What occurs just before the dissociation of RNA polymerase in Rho-dependent termination?

RNA polymerase interacts with Rho Signup and view all the answers

In bacterial transcription, which event follows the binding of RNA polymerase to the promoter?

Elongation Signup and view all the answers

What is the role of the GC-rich sequences in Rho-independent termination?

Facilitate hairpin formation Signup and view all the answers

What happens to the RNA polymerase as Rho approaches during Rho-dependent termination?

It slows down Signup and view all the answers

Which of the following best describes the type of protein Rho is?

A homohexameric protein Signup and view all the answers

Which strand of DNA serves as the template for transcription?

Template strand Signup and view all the answers

What is indicated by the sequence 'TTGACA' and 'TATAAT'?

They are promoter regions in DNA. Signup and view all the answers

Which of the following statements is true about the non-coding strand of DNA?

It does not code for the protein sequence. Signup and view all the answers

How does RNA polymerase synthesize mRNA during transcription?

By synthesizing it in the 5' to 3' direction. Signup and view all the answers

What can be inferred about genes found in an organism's genome?

Genes on different DNA strands usually do not overlap. Signup and view all the answers

Which direction does RNA polymerase move along the DNA during transcription?

5' to 3' Signup and view all the answers

Which sequence represents the coding strand of the given DNA?

5'-TTGACA TATAAT ATG TAA...-3' Signup and view all the answers

Which region of the gene corresponds to the initiation of transcription?

Promoter region Signup and view all the answers

Which of these sequences would likely NOT appear on the non-template strand of DNA?

ATG Signup and view all the answers

What is the function of the template strand during transcription?

It serves as a guide for synthesizing mRNA. Signup and view all the answers

What is the role of sigma factors in relation to RNA polymerase?

To assist RNA polymerase in binding to specific promoters Signup and view all the answers

What is produced when the core RNA polymerase binds with a sigma factor?

RNA Polymerase Holoenzyme Signup and view all the answers

Which sigma factor is primarily associated with general transcription in bacteria?

σ70 Signup and view all the answers

Which statement describes the process of transcription initiation in bacteria?

It requires RNA polymerase to first bind to the promoter sequence. Signup and view all the answers

What occurs during the abortive initiation phase of transcription?

RNA polymerase ceases activity after producing about 10 nucleotides. Signup and view all the answers

Once RNA polymerase enters the elongation phase, what happens to sigma factors?

They are lost from the complex, allowing RNA polymerase to move freely. Signup and view all the answers

How does the RNA polymerase Holoenzyme interact with the promoter?

It bends the DNA to facilitate binding. Signup and view all the answers

What are the two distinct complexes formed during transcription initiation?

Closed Complex and Open Complex Signup and view all the answers

Which sigma factor would be involved in the response to heat shock?

σ32 Signup and view all the answers

What type of interaction is essential for loading DNA onto RNA polymerase Holoenzyme?

Protein-DNA interactions Signup and view all the answers

In the context of sigma factors, how are different sigma factors characterized?

They recognize unique promoter sequences. Signup and view all the answers

What happens to the double-stranded DNA when the RNA polymerase Holoenzyme transitions from closed to open complex?

The dsDNA is opened to expose the template strand. Signup and view all the answers

Why is the presence of sigma factors important for transcription specificity?

They facilitate binding to specific promoter sequences. Signup and view all the answers

What signifies the +1 site in a bacterial promoter?

The transcription start site Signup and view all the answers

Study Notes

Bacterial Genes

A gene is a segment of DNA that codes information to produce protein or functional RNA
The expression of a gene is regulated by cellular mechanisms
A gene has two major components:
- Information to make functional protein or RNA
- Regulatory elements for expression

Bacterial Transcription, Schematic

RNA polymerase recognizes and binds to promoter elements (-35 and -10) causing DNA to open up
Transcription starts at the +1 site
RNA polymerase moves along the DNA template strand in the 5’ to 3’ direction
The non-template strand has the same sequence as the newly synthesized RNA (except for T replaced with U)

Template vs Non-template DNA strands

Template strand (non-coding): used as a template for transcription, does not code for the protein sequence
Non-template strand (coding): codes for the protein sequence, is not used as a template for transcription

Sigma Factors

Sigma factors assist RNA polymerase core to bind to specific promoters
Different types of sigma factors exist in a single cell
Sigma 70 (σ70) recognizes the typical bacterial promoter sequence (-35 and -10) and helps RNA polymerase core bind
RNA polymerase core bound to a sigma factor is called RNA polymerase Holoenzyme

Bacterial Transcription Initiation and Elongation

RNA polymerase creates a transcription bubble (approximately 10-20 bp) as it moves along the DNA template strand
The bubble exposes the template strand between positions -10 to +10

Three Stages of Transcription

Initiation: binding of RNA polymerase to a promoter sequence
Elongation: sequential addition of nucleotides to the 3’ end of the growing RNA using DNA as a template
Termination: Dissociation of RNA polymerase and release of a primary transcript from template

Transcription Initiation in Bacteria

RNA polymerase Holoenzyme carrying σ70 recognizes -35 and -10 elements
α subunits of RNA polymerase core recognize and bind to the UP element
When DNA binds to RNA polymerase, it gets bent. Initially, the DNA is not separated (Closed Complex)
RNA polymerase opens up the DNA (Open Complex) and generates the transcription bubble

Transcription Initiation: Abortive Initiation

RNA polymerase initiates synthesis on the opened template strand starting at the +1 site
Sigma factor blocks RNA polymerase core from moving too far from the promoter
Sigma factor disrupts polymerization and brings the core back to the +1 site
After a few attempts, RNA polymerase core breaks off from the sigma factor and enters the elongation phase

Transcription Elongation in Bacteria

RNA polymerase moves down the DNA and synthesizes the new RNA strand
The sigma factor is absent during elongation

Transcription Termination - Rho-independent

Occurs in regions of DNA where there is a highly GC-rich sequence followed by a U-rich region.
The GC-rich sequences are complementary to each other, resulting in a hairpin structure.
The U-rich region forms a weaker hydrogen bond with the template DNA.
The hairpin structure pulls the RNA away from the template DNA, destabilizing the bond and causing transcription to terminate.

Transcription Termination - Rho-dependent

Rho is a homohexameric protein that binds to the Rho Utilization Site (RUT) on the growing RNA.
Rho uses ATP hydrolysis to move along the RNA in the 5' to 3' direction.
When Rho approaches RNA polymerase, it interacts with the stem-loop structure of the RUT site on RNA, slowing down RNA polymerase.
This interaction causes RNA polymerase to dissociate from the DNA and RNA.

RNA Polymerase and Transcription

Initiation: RNA polymerase binds to a promoter sequence.
Elongation: RNA polymerase adds nucleotides to the growing RNA chain using DNA as a template.
Termination: RNA polymerase dissociates from the DNA, releasing the RNA transcript.

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Description

Explore the fundamentals of bacterial genes, including their structure and function. This quiz covers transcription mechanisms, the role of RNA polymerase, and the distinction between template and non-template strands. Test your understanding of gene expression regulation and sigma factors in bacterial systems.