Transcription

11/24/2014
1
TRANSCRIPTION
Department of Biochemistry, Kathmandu Medical College
Monday, November 24, 2014
1
Rajesh Chaudhary | @bloggerjesh
2
3
4
Prokaryotes vs Eukaryotes
Prokaryotes
rRNA: 23S, 16S, 5S
Eukaryotes
rRNA: 28S, 18S, 5.8S and 5S
Introduction of RNA
How is genetic information is executed?
Types of RNA
mRNA
tRNA
rRNA
Does our body have just these RNA or some more?
What is the role of RNA? (Structural, Catalytic)
5
Transcription
6
Catalytic RNAs are also known as RIBOZYMES.
What is the functional difference between DNA and RNA?
What are the differences and similarities between replication and transcription?
Entire structure or part of structure?

11/24/2014
2
Transcription / RNA synthesis
7
Similarities
Fundamental chemical mechanism
Its polarity (direction of synthesis)
Use of template
Similarities in phages (initiation, elongation and termination)
Differences
Use of primer
Segment
What is cellular transcriptome?
Transcription
8
DNA template is copied in the 3’  5’ direction
Synthesis of new RNA molecule = 5’  3’
Process of transcription
Initiation
Elongation
Termination
RNA polymerase
9
Core enzyme vs Holoenzyme
Termination factor
Steps in RNA synthesis
10
How long is a transcription unit? (I.e. Its extension)
What is the name of the product formed after transcription?
Initiation
RNA binding at promoter
Initiation of transcription
11
Pribnow box
-35 sequence
Mutation in either the Pribnow box or the -35 sequence can affect the transcription of the gene controlled by mutant promoter!
Elongation in transcription
12

11/24/2014
3
13
14
Supercoils are disentangled by topoisomerase I and II.
RNA polymerase synthesizes short transcript (<11 nucleotides) of DNA sequence.
Elongation begins when transcript is over 10 nucleotide in length.
RNA polymerase has no known proofreading function.
1.How fast nucleotides are added during the elongation step?
2.What is the error rate in transcription process?
15
1.Transcription is regulated at several steps
Termination of transcription
16
Termination
r-independent
r-dependent
r-dependent termination
17
r-factor: hexameric ATPase with helicase activity
Binds C-rich “rho” recognition site near 3’-end of the nascent RNA using ATPase activity.
ATP-dependent RNA-DNA helicase activity of rho separates the hybrid  new RNA
What does ATPase do?
18
s cycle

11/24/2014
4
Action of antibiotics
19
Antibiotics prevent bacterial growth by inhibiting RNA synthesis.
E.g.: rifampin, Actinomycin D
Transcription in Eukaryotes
20
Transcription in Prokaryotes Vs Eukaryotes
21
Differences
In terms of RNA polymerase
Eukaryotes: Pol I, Pol II and Pol III
a)Pol I: transcribes rRNA
b)Pol II: transcribes RNA that becomes mRNA
c)Pol III: transcribes tRNA & 5S RNA
Binding of polymerase is affected by enhancer sequence.
Similarities
Polymerase, dNTP, 3 steps of transcription
Chromatin structure and gene expression
22
DNA, histone, nucleosome and chromatin – how are they arranged?
Nucleosome
Chromatin
Euchromatin
Heterochromatin
Mechanism of chromatin remodeling
23
Chromatin
Inactive chromatin
Active chromatin
(Acetylation)
Enzyme: histone acetyl transferase
(Deacetylation)
Enzyme: histone deacetylase (restores +ve charge)
Eukaryotic gene promoter consensus sequences
24
Transcription factors recognize DNA through a variety of DNA-binding motifs, such as zinc fingers and leucin zippers.

11/24/2014
5
Transcription factors
25
26
Enhancer vs Silencer
27
What is transcription factors? Why is it necessary? Different transcription factor for different genes.
Coactivator: include the histone acetyltransferase proteins involved in chromatin remodeling.
Role of enhancers in eukaryotic gene regulation
28
Special cis-acting element
Increases process of transcription by RNA polymerase II
Located on the same chromosome where gene is located
Presence can be upstream or downstream to the gene
Possible locations of enhancer sequence
29
Inhibitors of RNA polymerase II
a-amanitin of Amanita phalloides
Post transcriptional modification
30
Both prokaryotic and Eukaryotic tRNA and rRNA is posttranscriptionally modified.
Prokaryotic mRNA is generally identical while eukaryotic mRNA is extensively modified.
tRNA are further modified to give a unique identity to each species.

11/24/2014
6
Post transcriptional modification of rRNA
31
ribonuclease
Post transcriptional modification of tRNA
32
nucleotidyltransferase
Post-transcriptional modification of eukaryotic mRNA
33
Primary transcripts are heterogeneous nuclear RNA (hnRNA).
Modification occurs in nucleus.
Modifications 1. 5’-capping 2. Addition of poly-A tail 3. Removal of introns
References
34

Transcription

Recommended

Recommended

More Related Content

More from Nepalgunj Medical College and Teaching Hospital

More from Nepalgunj Medical College and Teaching Hospital (20)

Recently uploaded

Recently uploaded (20)

Transcription