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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