W5 RNA synthesis and control in bacteria

Question 1

Transcription:

Answer 1

-Transfer of information from dsDNA template to a ssRNA molecule

Question 2

RNA synthesis:

Answer 2

-Transcription is catalysed by a single RNA polymerase in prokaryotes
-RNA is synthesised 5’-3’ to partner the template strand

Question 3

Important gene regions:

Answer 3

-Promoter region that is upstream of the start of the coding sequence (RNA polymerase interacts with this to determine the transcription start point)
-RNA coding region
-Transcription termination sequence (downstream sequence that stops transcription)

Question 4

Transcription promoters:

Answer 4

-2 sequences in E.coli that are critical for specifying the initiation of transcription, both located 35bp and 10bp before the start (-35 and -10 sequences).

Question 5

RNA polymerase holoenzyme:

Answer 5

-Consists of 4 polypeptide subunits bound to another polypeptide called the sigma factor which is essential for recognition of the promoter sequence

Question 6

RNA polymerase binding:

Answer 6

1) RNA polymerase binds loosely to -35 region with DNA still in double helix
2) Tighter binding follows involving local untwisting of ~17 nucleotides centered around -10 region

Question 7

RNA synthesis:

Answer 7

-RNA polymerase moves the ds DNA
-A ssRNA copy is synthesised by complementary base pairing with the template DNA strand
-RNA is synthesised from ribonucleoside triphosphates
-As RNA polymerase continues to move forward, the separated DNA strands reform the duplex

Question 8

Termination of transcription by hairpin loops:

Answer 8

-ssRNA forms secondary structures by folding up on itself
-Regions of complementary sequence within the RNA molecule produce antiparallel double stranded RNA regions separated by unpaired segments of RNA - forms ‘loops’
-Specific sequences at the transcription termination site cause the RNA molecule to assume a hairpin loop structure where RNA polymerase will stop transcription