Basic Transcription Part 2 Flashcards Preview

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Flashcards in Basic Transcription Part 2 Deck (36):
1

operon

- group of contiguous, coordinately controlled genes

2

inducible gene expression

- certain genes expressed under certain environmental conditions

3

cells will go on which first

- glucose
- then lactose use lac operon

4

one strategy to regulate gene expression

- group functionally related genes together

5

Beta-galactosidase

- used to break down lactose into glucose and galactose

6

all 3 genes transcribed together from

- 1 promoter to produce
- 1 mRNA = polycistronic mesage

7

each gene has its own

- ribosome binding site

8

lacY

- permease
- transports lactose into the cell

9

LacA

- transacetylase

10

lac operaton under negative control

- by the lac I repressor

11

lac I repressor

- tetramer of 4 identical polypeptides
- binds to operator next to promoter
- binds to operator and prevents RNA polymerase from binding to promoter and transcribing

12

repressor is an allosteric protein

- binding of one molecule changes shape of remote site
- allows interaction with a 2nd molecule

13

inducer

- binds repressor
- causes change in confirmation and dissociation from the operon.
- is lactose or allolactose

14

discovery of lac operon

- certain cryptic mutants expressed B-galactosidase, but could not metabolize lactose
- add radioactive galactoside to wild type and mutant bacteria
- only induced wild type took it up

15

jacob and monod suggest

- substance induced with b-gal to get galactosidase into cells
- mutants defective in this gene
- that gene was permease

16

constitutive mutants

- produced all 3 gene products all the time without induction
- also not capable of being repressed

17

idea of a repressor

- created merodiploids

18

merodiploids

- partial diploid bacteria
- had both wild-type (inducible) and constitute alleles
- wild-type dominant
- could turn off genes from constitutive and inducible parent
- wild type produces something that keeps lac genes off unless they are induced

19

predicted the existence of 2 key control elements

- repressor
- operator

20

deletion mutants

- also revealed promoter needed for expression of all 3 lac genes

21

existence of a repressor suggested

- a DNA sequence that binds the repressor
- operator

22

4 types of mutations

- (I^-) - recessive
- (O^c) - cis-dominant
- (I^s) - dominant in cis and trans
- (I^d) - uninducible

23

recessive mutation in the repression (I^-)

- I- mutations make a repressor that cannot recognize the operator
- mutations that eliminate the function of the repressor are recessive
- if combined with wild type will make inducible and repressible again

24

operator constitutive mutation (O^c)

- mutations in 1 of operators cause it to be active (unresponsive to repressor)
- other operator still repressible
- cis-dominant mutation

25

I^s mutations

- mutation in lac repressor
- some subunits can bind allolactose some cannot (make unresponsive to inducer)
- will poison system so neither lac operon will be inducible
- dominant in both cis and trans

26

I^d

- defect product can form defective tetramers with wild type repressor
- won't bind operator
- no way to repress operon
- whole tetramer inactive
- dominant negative (dominant in cis and trans)

27

repressor-operator binding

- add more repressor in presence of inducer - poor binding
- add more repressor in absence of inducer get increased binding till it levels off
- repressor binds to operator nicely in absence of inducer

28

O^c lac operator binding to repressor

- binds with lower affinity
- O^c lac operator requires more repressor for binding

29

what activates lac operon

- activation needed only in absence of glucose

30

glucose present

- repression keeps lac operon off

31

as glucose level drops

- cAMP level increases

32

Catabolite activation

- cAMP can activate lac operon even when some glucose is present

33

catabolite activator protein (CAP)

- binds to cyclic AMP

34

map near lac promoter

- at an activator site
- just upstream of promoter instead of downstream like activator
- called CAP binding site
- alpha-CTD of pol binds

35

cAMP and CAP effect on DNA

- cause the DNA to bend
- stabilizes the interaction

36

DNA bending leads to

- induced fit