The process of conversion of DNA to RNA or genome to transcriptome is called transcription. Central dogma of life or molecular biology both with pre-bioinformatics era & bioinformatics era is shown in flow chart. All the 3 stages of transcription i.e; initiation, elongation & termination are explained in this presentation. Information regarding DNA dependent RNA polymarase along with core enzyme & sigma factor is given in pictorial representation. The promoter sequence, hair-pin loop, Rho factor dependent & independent termination of transcription,post transcriptional modification of prokaryotic transcription before entering translation is also explained in detail.

1. SEMINAR ON PROKARYOTIC
TRANSCRIPTION
BSC BIOTECHNOLOGY 4th Sem
FACULTY OF LIFE SCIENCES
JSS ACADEMY OF HIGHER EDUCATION & RESEARCH
MYSURU
Miss AMRITHA S R
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Dated on :10-04-2018

2. OVERVIEW
 Central Dogma
 Transcription
 Initiation
 Elongation
 Termination
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3. THE CENTRAL DOGMA OF LIFE 3
DNA GENOME
RNA TRANSCRIPTOME
PROTEIN PROTEOME
REPLICATION REPLICATION
TRANSCRIPTION
TRANSLATION
Conventional Concept
(pre-bioinformatics era)
Current Concept
(bioinformatics era)

4. TRANSCRIPTION (RNA Synthesis)
 RNA is synthesised from a DNA template strand
 Enzyme: DNA dependent RNA polymerase (RNA
P°1)
 It adds ATP, GTP, CTP & UTP.
 Direction of synthesis: 5¹- 3¹
 It is a ‘De novo’ synthesis & existing 3¹-OH is not
necessary
 Only one strand of DNA is copied which is called
Template strand or the non-coding strand. The
other strand is called coding strand.
 Identical to the coding strand except with
‘U’s in place of ‘T’s
 Promoter sequence determines
transcription start sites RNA polymerase
has high affinity for these regions.
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Khans academy

5. TRANSCRIPTION is selective
 The entire molecule of DNA is not expressed in transcription.
 RNAs are synthesised only from some selected regions of DNA.
 For certain other regions of DNA, there may not be any
transcription at all.
 The exact reason for selective transcription is not known.
 Transcription involves three different steps
1. Initiation
2. Elongation
3. Termination
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6. Initiation
 The binding of RNA polymerase to DNA for the transcription to start.
 The specific region where RNA polymerase binds is called promoter region.
 There are 2 base sequences on the coding DNA strand which the sigma factor of RNA polymerase
bind.
1. PRIBNOW Box or TATA box : –10 region (6 nucleotide bases TATAAT 10 bases away on the left side)
2. The -35 sequence :second recognition site (bases TTGACA 35 bases away from +1 region)
3. +1 region(transcription start site)
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PROMOTER REGION
U Satyanarayana pg no.41

7. Core enzyme = α2ωββ¹ (constant)
σ subunit = σ (variable)
Holoenzyme = α2ωββ¹+σ
Purpose of σ subunit
Aids in binding gene & starting transcription
Hops off after a few nucleotides are added
Core enzyme continues polymerizing until
termination
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TRANSCRIPTION MACHINERY (RNA P°1)
U satyanarayana pg no.39
Khans academy transcription part 3

8. Elongation 8
 As the holoenzyme , RNA polymerase recognises the promoter region,the sigma factor is
released & transcription proceeds.
 RNA is synthesised antiparallel to the DNA template strand from 3¹ -5¹
 RNA polymerase uses (ATP,UTP,CTP,GTP) ribonucleotide triphosphates for the
formation of RNA
 RNA polymerase differs from DNA polymerase as it does not require any primers & does
not involve proof reading activity. However mistakes in RNA synthesis is less
dangerous, since they are not transmitted to the daughter cells.
U satyanarayana pg no.40
ELONGATION

9. Termination
 The process of transcription stops by termination signals
 There are 2 types of termination
1. Rho independent termination (ρ)
2. Rho dependent termination (ρ)
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wikispaces.psu.edu/display/230/Transcription
 ρ protein is not used
 Termination occurs when a hairpin loop is
formed in the mRNA by inverted repeats in
the template DNA.
 The sequence highlighted in red indicates
the G-C-rich region that forms the stem of
the hairpin loop through intramolecular
base pairing.
1) Intrinsic termination or Rho
independent :

10. 10
 In Rho-dependent termination, the
RNA contains a binding site for a
protein called Rho factor.
 Rho factor binds to this sequence
and starts "climbing" up the
transcript towards RNA polymerase.
 When it catches up with the
polymerase at the transcription
bubble, Rho pulls the RNA transcript
and the template DNA strand apart,
releasing the RNA molecule and
ending transcription.
 Another sequence found later in the
DNA, called the transcription stop
point, causes RNA polymerase to
pause and thus helps Rho catch up
2) Rho dependent Termination :
https://www.khanacademy.org/science/biology/gene-
expression-central-dogma/transcription-of-dna-into-
rna/a/stages-of-transcription

11. Post-Transcriptional Modification
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 The RNAs produced during transcription
are called primary transcripts.
 In prokaryotes transcription & translation
takes place in the cytosol as it does not
contain nucleus as a result there is no
time gap for post transcriptional
modification.
 Only in t RNA addition of CCA bases at 3¹
end is seen . It is done for the amino acids
addition in translation.
themedicalbiochemistrypage.org/images/tRNA-structure.png

12. Overall process
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U satyanarayana pg no.40

13. References
 Textbook of Biotechnology – U Satyanarayana
 https://www.khanacademy.org/science/biology/gene-expression-
central-dogma/transcription-of-dna-into-rna/a/overview-of-
transcription
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