1001(L18)-Transcription

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Questions and Answers

What is a key difference between RNA and DNA?

RNA uses ribose sugar while DNA uses deoxyribose. (correct)

RNA has a more stable structure than DNA.

RNA contains Thymine as a base while DNA contains Uracil.

RNA is double-stranded while DNA is single-stranded.

What are the components of ribonucleotides?

Nucleoside, ribose, and nucleotide

Base, sugar, and phospholipid

Deoxyribose, base, and phosphate

Heterocyclic base, sugar, and phosphate (correct)

Which statement about Uracil in RNA is true?

Uracil replaces Thymine in base-pairing. (correct)

Uracil is more stable than Thymine.

Uracil pairs with Cytosine.

Uracil does not pair with Adenine.

What kind of bond links nucleotides in RNA?

3',5'-phosphodiester bonds Signup and view all the answers

Which of the following statements is true about RNA structure?

RNA can form complex structures by folding. Signup and view all the answers

During transcription, which process follows initiation?

Elongation Signup and view all the answers

Which of the following components is not directly involved in RNA synthesis?

Ribosome Signup and view all the answers

What role do consensus sequences play in transcription?

They help recognize promoters for transcription initiation. Signup and view all the answers

What is the primary structural feature that enhances DNA stability compared to RNA?

Double helix structure Signup and view all the answers

Which type of RNA is primarily responsible for coding proteins?

mRNA Signup and view all the answers

What distinguishes RNA's susceptibility to hydrolysis from DNA?

Presence of a hydroxyl group on the 2' carbon Signup and view all the answers

Which type of RNA functions as an adaptor between mRNA and protein?

tRNA Signup and view all the answers

Which statement about RNA structures is correct?

RNA can form complex tertiary structures Signup and view all the answers

In terms of molecular weight, how is 1kb of mRNA related to protein coding?

1kb of mRNA codes for about 30kD protein Signup and view all the answers

Which types of RNA are classified as non-coding RNAs?

snoRNA and snRNA Signup and view all the answers

What is the measurement unit for RNA size?

Kilobases (kb) Signup and view all the answers

What effect does the presence of an OH group on Carbon 2 of ribose have on RNA?

Causes RNA to be unstable Signup and view all the answers

Which type of nucleoside triphosphate is more abundant in a cell?

NTPs (ribonucleic acids) Signup and view all the answers

Which enzyme is responsible for synthesizing RNA during transcription?

RNA polymerase Signup and view all the answers

During transcription, RNA synthesis occurs in which direction?

5’ to 3’ Signup and view all the answers

What unique characteristic does RNA polymerase possess regarding the DNA template?

It only transcribes one DNA strand (template strand) Signup and view all the answers

Which statement about RNA polymerase in E. coli is false?

It consists of multiple subunits Signup and view all the answers

Where is the promoter of a gene located in relation to the gene itself?

5’ of the gene Signup and view all the answers

What is the error rate for RNA polymerase during RNA transcription?

Approximately 1 x 10-4 Signup and view all the answers

What is the significance of E.coli in biotechnology?

It is used for the production of recombinant proteins. Signup and view all the answers

Which term describes a collection of genes regulated by the same stimulus?

Stimulon Signup and view all the answers

What is the primary enzyme responsible for transcription in bacteria?

RNA polymerase Signup and view all the answers

What is the function of transcriptional activators?

To increase the number of transcripts by facilitating RNA polymerase binding. Signup and view all the answers

What is the role of the promoter in transcription?

It is where RNA polymerase binds to begin transcription. Signup and view all the answers

Which of the following describes an operon?

One or more genes transcribed together under one regulatory site. Signup and view all the answers

Which of the following antibiotics specifically targets transcription?

All of the above Signup and view all the answers

What is the chain growth direction during RNA synthesis?

5′ to 3′ Signup and view all the answers

What is the primary role of the promoter in transcription?

It is a region of DNA where transcription factors can bind. Signup and view all the answers

What components make up the core RNA polymerase in E.coli?

2 α, 1 β, 1 β’, and 1 ω Signup and view all the answers

What are consensus sequences in the context of bacterial promoters?

Conserved nucleotide sequences determined by sequence comparison. Signup and view all the answers

What role does the sigma factor play in RNA polymerase activity?

It recognizes and binds to promoter regions. Signup and view all the answers

Which of the following is true about polycistronic mRNA?

It contains coding sequences for multiple proteins. Signup and view all the answers

What are the highly conserved sequences within the promoter that RNA polymerase binds to?

-35 and -10 regions Signup and view all the answers

How are different sigma factors significant in bacterial gene expression?

They allow expression of specific groups of genes. Signup and view all the answers

What is the Pribnow box known for?

It is the conserved -10 region of bacterial promoters. Signup and view all the answers

What is the primary role of the sigma factor s70 in E.coli?

To mediate the binding of RNA polymerase to specific promoters Signup and view all the answers

Which of the following sequences is part of the s70 promoter in E.coli?

TTGACA Signup and view all the answers

What is the role of transcriptional activators in relation to RNA polymerase containing s70?

They stabilize the binding to the promoter Signup and view all the answers

How does the sigma factor s38 differ from s70 in Escherichia coli?

s38 is specific for genes expressed during stationary phase Signup and view all the answers

What can inhibit the activity of sigma factors like s70 in E.coli?

Anti-sigma factors and proteins that regulate synthesis or degradation Signup and view all the answers

What is the approximate size of the sigma factor s70?

70 kDa Signup and view all the answers

What is one function of domain 2.3 in sigma factor s70?

To mediate binding to the -10 element Signup and view all the answers

How many different sigma factors are known to exist in E.coli?

Seven Signup and view all the answers

Study Notes

Lecture 18: RNA Synthesis - Transcription

Lecture delivered by Dr. Dinesh Balachandra, Lecturer (Non-Clinical), Biomedical Sciences, NUMed Malaysia.
Email address provided, but excluded as per instructions.
Previous lecture topics (L14-17) included DNA constituents (phosphate, deoxyribose, bases, nucleosides, nucleotides), Chargaff's rules, base pairing, DNA structure (fibre diffraction patterns and the Watson-Crick model), and DNA sequencing technologies.

RNA Synthesis: Transcription

DNA undergoes transcription to produce mRNA.
mRNA is then used to synthesize proteins.
The process involves a biological function.

What to Understand from Lecture 18

Understanding the components of the system for RNA synthesis (RNA polymerase and sigma factors).
Understanding promoters and consensus sequences.
Understanding transcription initiation, elongation, and termination stages.

RNA Structure

Images of RNA structure were presented.

RNA Characteristics

Chemically similar to DNA, but differing in key aspects.
Single-stranded, but can fold into complex structures.
Uses ribose instead of deoxyribose in its backbone, making it less stable.
Employs uracil (U) in place of thymine (T).

Ribonucleotides Components

Heterocyclic bases (adenine, guanine, cytosine, uracil, and thymine).
Sugar (ribose or deoxyribose).
Phosphate.
DNA uses A, G, C, T and deoxyribose.
RNA uses A, G, C, U and ribose.

Polymeric Structure of DNA and RNA

3',5'-phosphodiester bonds form the polymer backbone.

RNA Forms Secondary Structures

Uracil replaces thymine in base pairing (U-A base pairs).
Non-Watson-Crick base pairs are also common in RNA structures.
Image shows RNA structure.

RNA Size Measurement

Double-stranded DNA is measured in base pairs (bp). 1000 bp = 1 kbp, 1000 kbp = 1 Mbp
RNA is measured in bases (b). 1000 b = 1 kb
1 kb of mRNA codes for approximately 30 kD protein.

DNA vs RNA Stability

DNA is more stable than RNA due to its double-helix structure and the presence of repair mechanisms in the nucleus.
RNA is less stable and is susceptible to hydrolysis due to the presence of an OH group at the 2' carbon of the ribose sugar.

Classes of RNA Produced in Cells

mRNA: encodes proteins.
rRNA: structural component of ribosomes.
tRNA: adapts information between mRNA and proteins.
snRNA: involved in nuclear functions, including mRNA splicing.
snoRNA: processes/modifies rRNA.
Other RNAs involved in various cellular processes like telomeres, gene inactivation, and protein transport to the ER.

Transcription in E. coli

Illustrated diagram showing the process including promoter, transcribed region, and terminator.
mRNA can be polycistronic.

Transcription Promoters- Reminder

Promoter: located upstream (5') of a gene.
Contains specific nucleotide sequences for transcription factor association.
Transcription factors recruit RNA polymerase.
Conserved regions (consensus sequences) are identified.

How Consensus Sequences are Determined

Determined by sequence comparison across different promoters.
Diagrams and examples of promoter regions across various sequences are shown.

Identifying Consensus Sequences in Bacterial Promoters

Data presented in table and figure format to show consensus sequences and distances.

E. coli RNA Polymerase

Multisubunit enzyme, composed of core enzyme (β, β′, α, ω) and σ factor, to form the holoenzyme.

Transcription- RNA Polymerase

Core enzyme consists of 5 different subunits(β,β′, α, ω).
Sigma factor binds to the promoter.
Promoter region has highly conserved -35 and -10 sequences.

Sigma Factors

Different sigma factors allow the expression of different genes.
Sigma factor σ70 is the common one.
Other factors (σ38, σ32, σ28, σ24, σ19) exist for particular circumstances (stress response, stationary phase, etc.).

The E. coli σ70 Promoter

Diagram emphasizing the -35 and -10 consensus sequences.

Domains of σ70

Functions of the different domains (N- and C-terminal domains).

Alternative Sigma Factors

Alternative factors (e.g., σ38) are used for specific occasions and circumstances.

Termination

RNA polymerase stops transcription at terminator sequences.
Two types of termination (factor-independent and rho-dependent).

Factor-Independent Termination

Formation of a stem-loop structure in the newly synthesized RNA (complementary base-pairing).

Rho-Dependent Termination

Rho protein factor unwinds the RNA:DNA hybrid.

What We Covered Today (L18)

RNA structure.
Components of RNA synthesis (RNA polymerase, sigma factors, promoters, consensus sequences).
Transcription (initiation, elongation, termination).

Next Lecture (L19)

How transcription (and therefore gene expression) is controlled.

Points for Revision

Promoter definition, location and key sequence elements.
Consensus sequence definition.
Promoter influence on strength.
Core RNA polymerase subunit composition.
Promoter recognition subunit and related names.
Transcription initiation closed vs. open complex.
Sigma factor release time from RNA polymerase.
Transcription elongation process.
How self-complementary sequences drive termination.
Rho factor definition and function.

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