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Medical Cell Biology And Genetics > Topic 13.2: Transcription > Flashcards

Topic 13.2: Transcription Flashcards

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1
Q

what does transcription do

A

DNA -> mRNA

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2
Q

what does gene expression in transcription require

A

template - DNA
enzymes - RNA polymerase
substrates - NTPs
3 steps - initiation, elongation, termination

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3
Q

what are some key features of transciption

A

catalysed by RNA polymerase
hydrolysis of PPi by pyrophosphate drives reaction to form NTP
double stranded DNA template required and read from 3 to 5 end
NTP’s and Mg2+ needed
synthesis from 5 to 3 prime end

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4
Q

how is rRNA made

A

by RNA polymerase I

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5
Q

how is mRNA made

A

by RNA polymerase II

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6
Q

how is tRNA made

A

by RNA polymerase III

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7
Q

how many RNA polymerase are there in eukaryotes

A

3 in nucleus, 1 in mitochondria, 2 in chloroplasts

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8
Q

how many RNA polymerase are there in prokaryotes

A

1 copy: RNAP = bacterial RNA polymerase
the core enzyme of RNAP has 5 subunits - make random RNA
the holoenzyme has 6 subunit (core + sigma) - for the sigma binds to specific regions on the promoter to make specific mRNA

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9
Q

what is present in the promoter region and what occurs during transcription intiation

A

transciption factors
Transcription factors recognize the promoter. RNA polymerase II then binds and forms the transcription initiation complex.

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10
Q

in what direction to transcription factors binds

A

binding is directionally towards the TATA box
recognised by transcription factor in a directional way, so the polarity is important as otherwise transcriptional factor binds in the wrong direction and directionally bind the promoter

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11
Q

Transcription factors bind

A

to upstream sequences

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12
Q

how is gene expression regulated

A

the way transcipton factors bind to promoter controlls when a gene is expressed

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13
Q

what are the steps involved in transcription initiation

A
  1. TF binds to TATA
  2. more TF’s bind to upstream sequences
  3. RNA polymerase is recruited
  4. unwinding of DNA helix
  5. formation of a transcription bubble (17 base pairs)
  6. transcription initiates, directionally 5 to 3 end
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14
Q

why is only one of the double DNA strands being used as a template

A

as making RNA which is single stranded

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15
Q

what is involved in transcription elongation

A
  1. RNA synthesis from 5 to 3
  2. template strand is read 3 to 5
  3. single stranded RNA molecule is made
  4. as transcription bubble advance, DNA helix reforms behind it
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16
Q

what is being used as a template, coding and coding strand

A

DNA template is transcribed
- will be complementray to new RNA strand
- will be complementary to other DNA strand
thus, the non transcribed DNA strand is also the coding strand (same sequence of new RNA) and the transcribed DNA strand is the non coding strand/template strand

17
Q

what are some features of transcription termination

A

sequence dependent
results in primary RNA molecule
RNA processing needed to proudce mature RNA

18
Q

what is RNA processing

A

post transcriptional modification

19
Q

what is involved in RNA processing in rRNA and tRNA

A

chemical modifications and cleavage

20
Q

what is involved in RNA processing in mRNA

A

eukaryotes - capping (5 prime), slicing (middle) and tailing (3 prime)

21
Q

what is capping

A

a 5 prime Cap is being added and a methylaed G linked molecule added, which forms a 5-5 prime linkage
- provides protection and plays role in translation

22
Q

what is tailimg

A

lots of A being added to 3 prime end

- for protection and regulation

23
Q

what is splicing

A

highly accurate removal of introns and exons joined together
by spliceosomes
mature mRNA contains open reading frame plus 5 prime and 3 prime untranslated regions

24
Q

how many exons are there

A

always one more than intron

25
Q

splicing errors can cause

A

disease

26
Q

how is splicing used in regulation

A

can make different polypeptides from the same gene by splicing

27
Q

Chronological ‘replication order’

A 
Origin of replication recognition
Unwinding of DNA helix
RNA primers generated
DNA elongation from 5 to 3
Further helicase and primase activity 
DNA polymerase catalyse leading strand extension
Ozaki fragments joined by ligase 
Replication forks meet

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