Basic Transcription Part 2

Question 1

operon

Answer 1

• group of contiguous, coordinately controlled genes

Question 2

inducible gene expression

Answer 2

• certain genes expressed under certain environmental conditions

Question 3

cells will go on which first

Answer 3

• glucose

- then lactose use lac operon

Question 4

one strategy to regulate gene expression

Answer 4

• group functionally related genes together

Question 5

Beta-galactosidase

Answer 5

• used to break down lactose into glucose and galactose

Question 6

all 3 genes transcribed together from

Answer 6

• 1 promoter to produce

- 1 mRNA = polycistronic mesage

Question 7

each gene has its own

Answer 7

• ribosome binding site

Question 8

lacY

Answer 8

• permease

- transports lactose into the cell

Question 9

LacA

Answer 9

• transacetylase

Question 10

lac operaton under negative control

Answer 10

• by the lac I repressor

Question 11

lac I repressor

Answer 11

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

Question 12

repressor is an allosteric protein

Answer 12

• binding of one molecule changes shape of remote site

- allows interaction with a 2nd molecule

Question 13

inducer

Answer 13

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

Question 14

discovery of lac operon

Answer 14

• 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

Question 15

jacob and monod suggest

Answer 15

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

Question 16

constitutive mutants

Answer 16

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

Question 17

idea of a repressor

Answer 17

• created merodiploids

Question 18

merodiploids

Answer 18

• 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

Question 19

predicted the existence of 2 key control elements

Answer 19

• repressor

- operator

Question 20

deletion mutants

Answer 20

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

Question 21

existence of a repressor suggested

Answer 21

• a DNA sequence that binds the repressor

- operator

Question 22

4 types of mutations

Answer 22

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

Question 23

recessive mutation in the repression (I^-)

Answer 23

• 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

Question 24

operator constitutive mutation (O^c)

Answer 24

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

Question 25

I^s mutations

Answer 25

- 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

Question 26

I^d

Answer 26

- 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)

Question 27

repressor-operator binding

Answer 27

- 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

Question 28

O^c lac operator binding to repressor

Answer 28

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

Question 29

what activates lac operon

Answer 29

- activation needed only in absence of glucose

Question 30

glucose present

Answer 30

- repression keeps lac operon off

Question 31

as glucose level drops

Answer 31

- cAMP level increases

Question 32

Catabolite activation

Answer 32

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

Question 33

catabolite activator protein (CAP)

Answer 33

- binds to cyclic AMP

Question 34

map near lac promoter

Answer 34

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

Question 35

cAMP and CAP effect on DNA

Answer 35

- cause the DNA to bend | - stabilizes the interaction

Question 36

DNA bending leads to

Answer 36

- induced fit