Hipfner lecture 25 prokaryotic transcrption

Question 1

What is transcription initiation?
What is an operon?

Answer 1

-one of the main mechanisms for regulating genes in prokaryotes
-onetranscript unit coding for multiple proteins under a single promoter

Question 2

What is the is the sigma factor subunit of RNA polymerase binding, to do what?
What s the default state of genesis in prokaryotes

Answer 2

binds to -35/-10 promoter sequences to properly position the holoenzyme at transcription start site
-in prokaryotes, RNA polymerase easily binds the promoter – default state of genes is “ON”

Question 3

What is the positive regulation vs negtaive regulation, when is there transcription vs no transcription?

Answer 3

positive regulation: when activator is bound to DBD and when promoter is bound to rna pol, there is transcription
negative regulation-when repressor binds operator no transcription

Question 4

What happens when there is too much trp present?

Answer 4

-it will bind to trp repressor protein and shut off

Question 5

What are the components of the lac operon?

Answer 5

Lac I= repressor protein
-promoter P=where RNA pol binds to start transcription
operator O=where lac repressor can bind
Lac Z (beta gal gene)
Lac Y (permease Gene

Question 6

What happens when repressor binds lac operon?
What happens when there is lac permease in the cell?

Answer 6

-it prevents RNA pol from transcribing genes
-it binds to lac repressor protein to chnage its shape to not bind DNA, allowing inducible transcription

Question 7

What approach did Jacob and Monod take?
What did they use/

Answer 7

-they took mutagensis approach
-used biochemical assays to measure ß-
galactosidase and/or Lac permease activity in presence and absence of a synthetic inducer (IPTG)

Question 8

What did jacob and monod do to test the dominance/recessivness of the lac operon?
what did this also determine

Answer 8

J+M used “partial diploid” bacteria harbouring a plasmid that contains a second copy of the lac operon
-cis and trans acting factors

Question 9

Is the promoter a cis or trans acting element?

Answer 9

-cis acting
-it will affect the ability of Z )beta gal)and y (permease) to turn on

Question 10

What does an operator mutant affect?
WHat type of activity does it lead to?

Answer 10

-Oc (= O -) : constitutive… both β–Galactosidase and Permease are
constitutively active - failure to “keep off”
-similar to P, O only affects transcription of genes physically attached to it on the same DNA molecule – operator is a cis-acting element

Question 11

How does Operator mutant lead to constituitive activation?

Answer 11

-repressor is unable to bind to Oc, so Z and Y are induced when present