Download DNA ------------> RNA Transcription RNA processing

Gene expression
DNA ------------> RNA ------------>
Transcription RNA processing
----------->Protein
Translation
1) 5’ capping
2) 3’ Poly A tails
splicing
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Gene expression
DNA ------------> RNA ------------>
Transcription RNA processing
----------->Protein
Translation
1) 5’ capping
2) 3’ Poly A tails
splicing
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Translation
Bacterial mRNA
Ribosome
Binding site
Coding sequence
Determines seq of amino acid
Start codon
Stop codon
Fig 12.11
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Translation
Codon:
A sequence of 3 nucleotides that specifies a particular amino acid
Genetic code is
Degenerate
(=more than one codon
specifies
a particular amino acid
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Discovery of The Genetic Code
Use of synthetic RNA
AAAAAAAAAAAAAAA
=> Lys-Lys-Lys-Lys-Lys
UUUUUUUUUUUUUUU
=> Phe-Phe-Phe-Phe-Phe
15 NT => 5 a.a
3 NT / 1 a.a
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Discovery of The Genetic Code
1) Add RNA triplet : e.g., CCA
Ala*+
19 other aa
Leu*
19 other aa
pro *+
19 other aa
2) Add mixture of 20 tRNA(next page
) attached to each a.a with only one a.a being
radioactively labeled
+ribosome
tRNA
Specialized RNA that functions in transferring an amino acid
to growing peptide sequence
Structure of tRNA
3’ single
stranded
region
Amino acid
attach site
Fig 12.14
Anti-codon
Complementary to
codon sequence
CCA
G
G
U
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Translation
3) Isolate tRNA bound ribosome by filtering
4) Determine which tube has radioactivity
CCA codes for proline
Ala*+
19 other aa
Leu*
19 other aa
pro *+
19 other aa
Translation
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Translation
mRNA,
tRNA,
ribosomes,
translation
factors
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tRNA
Fig 12.14
Structure of tRNA
3’ single
stranded
region
Amino acid
attach site
Anti-codon
Complementary to
codon sequence
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Aminoacyl-tRNA -synthetase
Fig 12.15
- Catalyzes the attachment of amino acids to tRNA by using ATP
- 20 types of amino acyl-tRNA synthetase exits (one for each a.a)
1) Binding of Amino acid & & ATP
a.a is tansfered to
tRNA
Charged
tRNA
Aminoacyl-tRNA -synthetase
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Ribosome
Fig 12.16
Large
subunit
Exit site for
tRNA
E site
P site
Actually synthesis
Of a.a chain
A site
Charged tRNA come in
small
subunit
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3 stages of translation
Initiation
Elongation
Termination
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3 stages of translation
Initiation
1) Small subunit binds to
mRNA
2) Initiator tRNA comes in
3) Large subunit comes in
Initiator tRNA
mRNA
Use
GTP as energy source
Fig 12.18
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3 stages of translation
Initiator
tRNA
mRNA
Initiation
Elongation
Synthesis
from start
codon to stop codon
Termination
Disassembly of the complex
at stop codon releasing
Polypeptide
Fig 12.18
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Translation
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Gene regulation
DNA ------------> RNA ------------>
Transcription RNA processing
----------->Protein
Translation
1) 5’ capping
2) 3’ Poly A tails
splicing
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Gene regulation at the level of translation
Example
Iron toxicity in mammals
Iron
is a vital cofactor for many cellular enzymes
However, it is toxic at high levels
Ferritin : protein that can bind to excess iron
When there is high iron
=> Hight ferritin
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Gene regulation at the level of translation
Iron toxicity in mammals
Low iron in cytosol
IRP (iron regulatory
protein) binds to IRE
ferritin
mRNA
Inhibition of ferritin
translation
high iron in cytosol
Iron binds to
IRP=>inhibit binding
of IRP to IRE
ferritin translation
Fig 13.22
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Gene regulation
DNA ------------> RNA ------------>
Transcription RNA processing
----------->Protein
Translation
Point of regulation
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