RNA synthesis:

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Lecture 12 Chapter 11 RNA synthesis Transcription
of the genetic code
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DNA synthesis on the lagging strand.
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Proofreading in replication and DNA polymerase
I.
Goal lt 1 error (infidelity) in 109-1010 base
pairs.
Mismatch in hydrogen bonding causes 1 error in
104-105 base pairs. Need a way to correct
this. Also need to remove the primer. Mutations
uv light, chemicals.
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• Multiple layers to this process.
• DNA polymerase III can remove
• the last base added correct it.
• 2. DNA polymerase I can replace up
• to 10 bases.
• Other mechanisms which we are
• not going to talk about.

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DNA polymerase I can do more..
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1. DNA polymerase I can remove up to 10
nucleotides from the 3 end. 3-5
exonuclease. remove mistakes remove the primer

2. It can replace the nucleotides it has
removed with the correct ones.
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Transcription Synthesis of RNA from a DNA
template.
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• Table 10.1
• RNA is initially synthesized using
• a DNA template in the process
• called transcription.
• The enzyme is DNA-dependent
• RNA polymerase.

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Coding strand
Template Strand.
RNA polymerase
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• Two strands of DNA
• Template strand (-strand)
• 2) Coding strand (strand)

RNA polymerase reads this 3 to 5
The RNA synthesized will have the same sequence
as this except the T will be replaced by U.
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RNA is synthesized 5 to 3
The template strand of DNA is read 3 to 5.
By convention, control sequences are read 5 to
3 on the coding strand. 5 end upstream 3
enddownstream.
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How does RNA polymerase know where to
start? Site on the DNA promoter Sigma factor
part of the polymerase
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Recognition on the DNA
Promoter region (upsteam)
Consensus sequence
-35 region
TSS(1)
Pribnow box
Translation start site
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Recognition by the polymerase
RNA polymerase 4 kinds of subunits a2, b, b
and s.
b b make up the active site.
a2, b, b makes up the core enzyme.
s is loosely bound tells the enzyme where to
start which strand to read.
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The s binds to a promoter region on the DNA
tells it where to start which strand to
read. It drops off after about 10
nucleotides have been added. More than 1 type of
s factor.
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• Transcription can be divided into
• 3 parts.
• Chain initiation
• Chain elongation
• Chain termination.

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RNA pol
1. Chain initiation.
Step 1 s recognizes promoter
DNA template
Step 2 closed complex formed.
Fig 11.3
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Step 3 Open complex formed.
Purine NTP
Step 4 Add nucleotide triphosphate
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2. Chain elongation.
NTP
Step 5 Chain elongation takes places
Transcription bubble
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• 3. Chain termnation
• Intrinsic termination.
• inverted repeats.

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Inverted repeats.
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Tranlation termination by the rho factor.
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• Table 10.1
• RNA is initially synthesized using
• a DNA template in the process
• called transcription.
• The enzyme is DNA-dependent
• RNA polymerase.

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2. All four ribonucleotides are required
(ATP, GTP, CTP and UTP and Mg2.
3. A DNA template is needed but an RNA primer
is not.
4. Synthesis is from 5 to 3 The nucleotide
at the 5 end keeps its triphosphate. ppp
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5. The enzyme uses one strand of the
DNA as a template.
The base sequence of the DNA contains base
sequences for initiation and termination.
The template strand is read in the 3 to 5
direction.
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6. The template is unchanged.