1 gene transcription,post- transcriptional processing & reverse transcription
TRANSCRIPT
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Gene transcription,post-transcriptional processing & reverse transcription
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1.Concept
A. Enzymes involved in
transcription
a. RNA polymerase
( DNA-dependent RNA
polymerase,DDRP )
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require:
(1) four NTP
(2) Mg 2+ or Mn 2+
(3) DNA template
(4) synthesis direction
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Products:
single strand RNA
containing DNA heredity
information
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• RNA pol in prokaryotes
( E.coli RNA polymerase )
* functions
* constitute
four subunites
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core enzyme & holoenzyme
• RNA pol in eukaryotes
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• RNA pol in eukaryotes
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Type I II III
location nucleoli nucleoplasm ucleoplasm
products 18s,5.8s, pre-mRNA, RNA,5sRNA
28s rRNA hnRNA U6
sensitivity none +++ +
to a amantin
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B. Process of transcription
initiation, elongation, termination
a. the initiation stage
• promoter
* concept
* characteristics
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*Promoter of prokaryotes
-10bp-------TATAAT
(TATA box)
(pribnow box)
-35bp------- TTGACA
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Promoter of eukaryote -25bp-------TATAAT (TATA box) (hogness box -40bp------- GCbox -110bp-----CAAT box
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-110 -40 -25 +1
CCAAT
box
GC
boxTATA
box
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GC or CAAT box both in
sense or antisense strand all
effective
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antisense strand
(template strand, (-)strand,)
Sense strand
(coding strand,(+)strand)
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DNA: antisense
5’AACGTTACCGATC 3’
3’TTGCAATGGCTAG 5’
sence
mRNA
UUGCAAUGGCUAG
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• synthesis direction
5’ 3’
• characteristic of
transcription-----
asymmetrical transcription
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• enhancer
*concept
* characteristics
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• cis -acting element
*concept
• trans-acting element
*concept
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b.elongation stage
• the transcription
products elongate along
the 5’to 3’
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• the RNA pol moves
along the 3’ to 5’
• 50 nucleotides/second/per
molecular enzyme
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• newly synthesis
DNA-RNA hybridized
strand is unsteadiness
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C.termination
* concept
*the type of termination
a.Rho()-dependent
termination
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*the structure of Rho factor
*the functure of Oho factor
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b.Rho()-independent
termination
the special region in the
DNA template
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B.inhibitors of transcription
E.summarize
a.RNA pol
b.process
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initiation
elongation
termination
c. characteristics
of transcription
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d. the different of mRNA
transcription in prokayotes
& eukaryotes
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Prokaryotes eukaryotes
Policistronic transcript monocistronic transcrip
Transcription coupled with translation seprate
No processing processing
Shorter half life longer half life
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C.post –transcriptional
processing in eukaryotes
1.processing of mRNA
(1) capping of mRNA
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* The structure of cap
mGpppG
* The process of capping
*the functure of cap
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(2) Added poly A tail in
mRNA 3’end
* The structure of tail
* The process
*the functure of tail
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(3) Splicing
remove intron,
join exon,
mature mRNA
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snRNA & snRNP
exit RNA processing
event
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(4) RNA editing
* concept
* significant
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2.processing of rRNA
* quantity
* type & arrangement
* site
* process of processing
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Ribozyme
discovery
concept
structure
functure
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3. processing of tRNA
* remove 5’end sequence
* CCA is added in 3’end
* multiple internal bases
are modified
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D. reverse transcription
1.retrovirus & reverse-
transcriptase
(1) History
1964 Temin
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found RNA virus
1970 found reverse -
transcriptase
(2) The function of reverse -
transcriptase
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RNA as template
Four dNTP
Produce DNA containing
RNA heredity information
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reverse – transcriptase
(RNA dependent DNA polymerase,RDDP)
its function:
RNA dependent DNA polymerase
RNA hydrolyse
DNA-dependent DNA synthetase
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(2) Genome of ASV
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(3) Life cycle of retrovirus
two stage:
* RNA reverse transcription
DNA provirus
intergrate into host cell
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* DNA transcription
mRNA
Protein
virus particles
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2.oncogen& tumer suppressor
gene
(1) concept of oncogen
& pro-oncogen
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(2) proto-oncogen
become oncogene
*enhanced expression
*mutatiom
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(3) Products &function of
pro-oncogene
* grows factors
*trans-membrane receptors
*transducers in the cell
*transcriptional factors