Transcription

Question 1

transcription

Answer 1

DNA to RNA

Question 2

Types of RNA

Answer 2

Polycistronic = codes more than one protein
Monocistronic = codes single protein

Question 3

differences between DNA and RNA

Answer 3

Extra OH in RNA makes it more susceptible to hydrolysis, DNA uses ATGC, RNA uses AUGC, DNA = double helix and RNA = single stranded

Question 4

what’s needed for transcription

Answer 4

Template DNA = coding/sense strand, ribonucleoside triphosphates, RNA polymerase and transcription factors

Question 5

Phases of transcription

Answer 5

initiation, elongation and termination

Question 6

initiation

Answer 6

RNA polymerase slides along DNA and unwinds, recognises promoter, specific DNA sequence

Question 7

prokaryotic RNA polymerase

Answer 7

Has 5 polypeptide subunits but only recognises promote when 6th sigma factor associates with complex, sigma factor also anchors RNA polymerase to DNA stand so must dissociate before elongation

Question 8

strong promoters

Answer 8

frequent initiation

Question 9

Weak promoters

Answer 9

Initiate every 10 mins

Question 10

eukaryotic RNA polymerase

Answer 10

Bind to promote upstream of transcriptional start site eg TATA box, no direct equivalent to sigma subunit, instead assembles transcription factors which associate with specific DNA sequences in gene promoter and recruit RNA polymerase to start transcription

Question 11

elongation

Answer 11

As RNA polymerase moves along it unwinds, genes transcribed simultaneously by several RNA polymerases, nucleotides added to growing 3’ end of RNA molecule, transcription bubble formed throughout

Question 12

transcription bubble

Answer 12

Segment of DNA around 17 no that remains unwound throughout transcription

Question 13

prokaryote termination

Answer 13

polymerase stops transcription at end of terminator, mRNA translated without further modification

Question 14

prokaryotic factor-independent termination

Answer 14

relies on GC rich sequence near end of transcribed region, when transcribed into RNA it base-pairs with itself and forms stem loop, cases RNA polymerase to stall, short region of H-bonding between 3’ end of RNA transcript and DNA template is weak and easily dissociated and transcription is teminated

Question 15

Eukaryotic termination

Answer 15

RNA polymerase II transcribed polyadenylation signal sequence, RNA TRANSCRIPT RELEASED 10-35 nucleotides past poly-A sequence, actual 3’ end determines during RNA processing