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Medicine 1 > 7. Gene expression > Flashcards

7. Gene expression Flashcards

1
Q

what is the enzyme that carries out transcription

A

DNA- dependent RNA polymerase

  • multisubunit complexes
  • couples ribonucleoside triphosphates (driven by hydrolysis of PPi)
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2
Q

Difference between polymerase in bacteria and eukaryotes

A

bacteria contain one enzyme that makes most of the RNA and eukaryotees contain 4 or 5

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3
Q

describe prokaryotic RNA polymerase

A
  • holoenzyme: sigma subunit enables RNA polymerase to recognise promoter regions in DNA
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4
Q

holoenzyme

A

sigma subunit and core enzyme

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5
Q
A
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6
Q

name of template DNA

A

antisense/ non coding strand

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7
Q

DNA sequence that has the same sequence as RNA

A

sense/ coding strand

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8
Q

protein coding genes in eukaryotes and prokaryotes

A

structural genes

eukaryotes: transcribed individually
prokaryotes: tandem layout and transcribed together- operons giving rise to polycistronic mRNA

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9
Q

How does RNAP recognise the correct DNA strand and initiate at the beginnning of a gene?

A

Binds to base sequence promoters

in bacteria promoter regon is reocognised by sigma factor (adaptor)

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10
Q

What are promoters

A

40 bp sequence on 5’ side of transcription start site upstream of RNA starting nucleotide

written by sense strand so matches directionality of transcribed RNA

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11
Q

What is the number assigned to the first base pair

A

+1 (no zero base)

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12
Q

What is the pribnow box

A

a common sequence in the promoter region in prokaryotes

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13
Q

Why can we identify promoters?

A

RNAP’s tight binding protects the sequence from being broken down by endonucleas DNAse I

mutations can effect RNAP binding

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14
Q

what does RNAP holoenzyme binding lead to

A

DNA ‘melting’ (separation) in its vicinity

  • transcription bubble

allows complementary RNA strand synth.

bubble travels with RNAP

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15
Q

RNAP is processive- explain

A
  • does not dissociate from template
  • 1900 bp, up to 180 rotations
  • lots of reactions until it leaves
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16
Q

Describe the nature of transciption

feature of transcription in prokaryotes

A

rapid

RNA synth is initiated as often as sterically possible

protein synth can begin before RNA is completely synthesised

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17
Q

Do eukaryote RNAP contain a sigma factor

A

no

acessory proteins ID promoter and recruit RNAPs

18
Q

Transcription termination in prokaryotes

A
  • Contains series of 4-10 A•T bases
  • A G + C-rich region with a palindromic sequence

The RNA transcript (‘intrinsic terminator’) forms a self-complementary “hairpin”

  • causes RNAP to pause
  • permits RNAP conformational change allowing termination
19
Q

What happens if E.coli do not display the intrinsic terminator

A

need the Rho factor

  • a helicase that runs along RNA until encountering a paused RNAP
  • Pushes RNAP, causes rewinding of dsDNA & release of RNA
20
Q

Eukaryotic RNAP

A
21
Q

eukaryotic vs prokaryotic RNAP

A

eukaryotic have a larger mass and greater subunit complexity

22
Q

RNAP II promoters are…

A

complex/ diverse

if they are selectively expressed they contain consensous sequences such as TATA box ( equivilent to Pribnow box)

25 bp upstreat from TSS

23
Q

sequences that encourage transcription

A

enhancers

recognised by transcription factors which can stimulate RNAP II binding and mediate selective gene expression in eukaryotes

24
Q

what can DNA bending do

A

cause an enhancer that is far from the promoter to interact with transcription-initiation complex

25
Q

General transcription factors

A

required for RNAP II transcription

equivalent of σ factor

other gene specific factors can enhance

26
Q

General transcription factors combine with enzyme and DNA to form

A

preinitiation complex

27
Q

where are GTF targeted to

A

TATA box by TATA binding protein

28
Q

what do eurkaryotes lack and what is done to overcome this

A

precise transcription termination sites

transcript processing takes place later

29
Q

Inhibitors of transcription:

RIfamycin

A

inhibit prokaryotic but not eukaryotic transcription, side effects

Makes RNAPs stay in the promoter region, so proteins cannot be made until bacteria runs out of protein

Prevent elongation (not promoter binding /initial bond formation)

  • Inactivated RNA polymerase remains bound
  • blocks further initiation
30
Q

Inhibitors of transcription: Actinomycin D

A
  • Binds to duplex DNA (intercalates) RNAP and DNA polymerase cannot get past
  • Inhibits DNA replication & transcription of eukaryotes & prokaryotes
  • Interferes with polymerase passage
31
Q

Inhibitors of transcription: death cap

A

contains α-Amanitin

•tightly binds to RNAP II

  • blocks the elongation step
  • binds beneath the polymerase’s bridge helix
32
Q

post-transcriptional processing: prokaryotes

A

not processed much

33
Q

post transcriptional processing in eukaryotes

of hnRNA

A

5’ cap

polyadenylated 3’ end

splicing

RNA exported from nucleus

techinically processed whilst theyre being synthesised

34
Q

RNA capping

functions

A

RNAP contains C terminal domain

when phosphorylated it recruits capping enzyme complex

the 5’ end is modified to 7-methylguanosine (type O cap) joined by 5’-5’ triphosphate bridge

resist degradation

efficient initiation of translation

35
Q

Polyadenylation

A

influences mRNA stability

Complex with Poly(A)-binding Protein (PABP) & prevents degradation.

36
Q

intron consenscous sequences

A

Found in the “GU-AG” Introns- act as recognition for RNA-binding proteins.

37
Q

how are introns removed

A

hydrolysis

38
Q

what is needed for splicing

A

spliceosome –snRNAs and proteins = snRNP

39
Q

why are introns paradoxical

A

mutations can lead to disease

40
Q

why is splicing needed

A

can produce different proteins (different destination of cell and activity) by alternative splicing

Medicine 1 (53 decks)

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