BC 16 Transcription Flashcards Preview

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Flashcards in BC 16 Transcription Deck (19):
1

Similarities to Replication

phosphodiester bonds linking nucleic acids

5-3

new strand complementary to tamplate strand

2

Differences

ribonucleotides

Uracil instead of thymine

RNA product gets displaced

RNA pol does not need primer

Only for specific genes

Many copies

3

Types of RNA

mRNA: coding sequence

tRNA: protien synthesis

rRNA: ribo RNA, makes ribos

snRNA: mRNA splicing

4

RNA pol

Prok: single RNA pol

Euk
RNA Pol 1: transcribe three major rRNA (5.8s 18s 28s)

RNA pol II mRNA

RNA pol III: tRNA (some rRNA and snRNA)

5

Transcribed region

5' UTR (untranslated region)

AUG, protien coding region

3' UTR,

STOP

6

Prokaryotic transcription

RNA pol Six subunits
-catalyzes RNA synthesis but cannot initiate elong.
2 alpha
1B
1B'
1 omega

-facelitates polymerase binding to DNA at -35 and -10 promoter elements
Sigma subunit
1 sigma

7

Prokaryotic promoter

from +1 back to -35. Includes -10.

Binds RNA pol

-10 = AT rich- easier to unwind and bend to initiate transcription:
-consesnsus sequence:conserved across genes. Polymerase will always recognize the appropriate binding site



8

Prokaryotic transcription

1. Initiation: RNA pol holoenzyme binds to -10 and -35 using sigma subunit (below) (DNA not unwound) (promoter melting)

2. open promoter complex- Unwinding of DNA around the initiation site. (does not need helicase)

3. RNA pol makes 10 nucleotides short transcript, the sigma subunit is then released.

4. elongation begins
-only about 15 bp long bubble, RNA pol unwinds and religates

5. TERMINATION: signal sequence DNARNA is released
-Rho independant: intrinsic, spontaneous, no protein needed. Hairpin disrupts RNA pol releases it
-Rho dependent term: rho binds to rho recognition site, when RNA pol is paused at term site, ATP dependant helicase activity of Rho separates RNA DNA hybrid helix. releases RNA


WHY have two??

9

Rifampicin

antibiotic interfere with RNA synthesis

usd to treat TB, wims and Weings tumors, test. cancer, carcomas, (dactinomyycin)

-action: inhibits transcription by binding to B subusing of prok polymerase. Prevents growth

10

Eukarytotic Transcription differences

THREE RNA pols

numerous IF's and GTF (general transcription factors) to initiate transcription

11

Eukaryotic Trancription Initiation complex

DRAW

1. TFIID Binds to the AT rich promoter (TATA Box)
-multisubunit compled of TFIID contains Tata binding protiens (TBP)(allows TFIID to recognize tata)

2. TFIIA assists with TFIID binding to tata

3. TFII B orients the polymerase

4. RNA pol II bound to GTF at teh promoter -carboxy terminal domatin (CTD) or RNApol II held in place by GTF's

5. TFII E intereactes with promoter bound RNA pol II

6. TFII E recruits and regulates TFIIH
-binding of TFIIH completes the pre initiation complex (PIC)

12

Euk Transcription Initiation

7. TFIIH is a multisubunit protein that has two activities
-helicase: ATPase unwinds dna at initiation site
-kinase: phosphorylates C terminal domain of RNA pol II

-phosphorylated CTD no longer binds to GTF's and releases GTF's

-elongation begins wit just RNA pol II

terminated at stop codon

13

5' Cap

Occurs first, addition provides direction of where go to and stabilizes

-7-methylguanosine (methylated guanasine molecule at position 7 of purine ring) as soon as mRNA synthesis begins. first and second nucleotides can be methylated too

protects from DNA by stabilization

positions mRNA for initiation of translation

14

3' pA addition

Occurs after 5' cap. pA added for stabilization

15

Splicing of Introns

Last post transcription mod

not yet spliced referered to as primary transcript or pre mRNA

15% inherited human disease splicing errors

GU- 5" splicing
A: branch point of lariat formation
AG: site of splicing at 3" end.

1. cleavage of 5" end
2. folding for intron to a lariat stucture at branch point
3. cleave at 3' end
4. assembly of neighboring exons
5. lariat degraded in nucleus

snRNA: splicosomes, five types of RNA combined with over 200 snRNP.
Splice AND ligate exons

16

alternate splicing:

most premRNA contains multiple introns diffeerent mRNA ca be produced from the same gene by diff. combinations.
variants of muscle cells

17

polyadenylation

promary transcript cleaved 10-35 nucleotides downstream from AAUAAA sequence in nucleus.

Enzyme poly A polymerase adds othe at a time ~200 nucleotides to the 3' end produced b cleavage

-stability
-signal for transport out of nucleus
-translation, intereacts with 5' cap

18

Reverse transcription

DNA-> RNA

lacks introns, found in genomic version of same gene.

cDNA

virus can integrate DNA to be replicated and transcribed.

19

chart

differences chart at end