bacterial gene expression Flashcards Preview

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Flashcards in bacterial gene expression Deck (28):
1

transcription unit

-a sequence of DNA bases that is transcribed to give a single, discrete complementary RNA
-In bacteria, multiple genes can be in the same transcriptional unit, this is termed an operon

2

promoter site

-a special region of DNA where RNA pol binds for the purpose of initiating transcription (-35 and -10 regions are two key elements of most promoters)

3

termination site

-a site within the DNA or RNA product at which RNa synthesis stops

4

inhibitors of RNA synthesis

-bind to beta subunit of RNA pol
-rifamycin: blocks elongation (rifampicin)
-lipiarmycins: blocks initiation (fidaxomicin)

5

sigma subunit of RNA pol

-necessary for recognition of the promoter region of a gene

6

two forms of RNA pol

-holoenzyme and core enzyme
-holoenzyme releases the sigma subunit upon binding the promoter, transcription is initiated, and becomes the core enzyme

7

the role of the sigma subunit

-causes very stable binding at promoter regions
-reduces binding at non-promoter regions of DNA (specificity)
-removal of gama allows escape from the promoter (translocation) and elongation of the transcript
-only one type of RNa pol, but many types of gama subunit which recognize promoters with different sequences

8

holoenzyme composition

-2 alpha
-2 beta
-1 sigma

9

core enzyme composition

-2 alpha
-2 beta

10

how does transcription stop

-factor dependent termination
-factor independent termination

11

factor independent termination

-site is encoded in the DNA sequence appearing as a region of dyad symmetry

12

factor dependent termination

-Rho factor binds directly to RNa polymerase and causes the polymerase to stop and release when reaching the factor dependent terminator

13

regulation of transcription

-positive regulators bind upstream of the promoter
-negative regulators can overlap the promoter or be downstream

14

organization of toxin genes, pathogenicity locus

tcdR, tcdB, tcdE, tcdA, tcdC

15

tcdR

positive regulator

16

tcdB

toxin B

17

tcdE

holin

18

tcdA

toxin A

19

tcdC

negative regulator

20

operon of toxin genes

toxin B and holin

21

when is the toxin produced

during stationary phase

22

CodY

-represses the toxin gene by binding to the promoter of tcdR
-Ile dependent activation
-active during exponential growth phase due to abundant Ile
-inactive during stationary phase

23

toxin regulation: nutrient excess and nutrient limitation

-excess: cody is active and inhibits the RNA pol from binding, tcdC is synthesized which inhibits tcdR
-limitation: CodY is inactive, bacteria are in the stationary phase, and TcdR is promoting the

24

what causes high toxin production?

-mutation in tdcC that inactivates the protein

25

tcdR is inactive when

associated with tcdC

26

codY active when

associated wiht Ile
-in the active state, CodY represses toxin expression
-this is a negative regulator active in nutrient excess

27

rifamycin

ex: rifampycin: blocks elongation by the RNa pol

28

lipiarmycins

ex: fidaxomycin, blocks initiation