lectures 8 & 9 - control of gene expression in bacteria

Question 1

whats the def of a gene

Answer 1

a DNA segment that contributes to phenotype/function. In the absence of
demonstrated function a gene may be characterized by sequence, transcription,
or homology

Question 2

what is an operon

Answer 2

a unit of bacterial gene expression and regulation, including
structural genes and control elements in DNA recognized by regulator gene
product(s)

Question 3

how long are mRNA ½ lives

Answer 3

short: 1-3 min

Question 4

what is a promoter

Answer 4

where RNA polymerase binds

Question 5

what is an operator

Answer 5

where regulatory proteins bind and this controls what happens at the promoter

Question 6

where are the promoters/operators in regards to structural genes and each other

Answer 6

upstream but can be in either order

Question 7

what is constitutive gene expression

Answer 7

genes expressed most/all time

Question 8

what is inducible gene expression

Answer 8

set of genes that are transcribed only as response to something in the environment

Question 9

what is repressible gene expression

Answer 9

gene expression switched off in response to substance in env (often anabolic or biosynthetic pathways)

Question 10

what type of expression is the lac operon

Answer 10

inducible system

Question 11

when are lacZ,Y,A expressed and what prevents this when it is not there

Answer 11

only expressed when lactose (or analogues) are present

when no lactose, the lacI repressor binds to DNA at operator preventing RNA polymerase binding at promoter (there is a very low level of lac expressed)

when there is lactose, LacI has conformational change

Question 12

how do operon inducers usually compare to substrates for the enzymes

Answer 12

usually small molecules that are identical or very close to substrate for the enzymes

Question 13

what are trans-acting mutations

Answer 13

mutations that can act at a distance, not simply in the DNA
molecule in which they occur. (Usually affects production of a diffusible protein)

Question 14

what are cis-acting mutations

Answer 14

site affects the activity only of sequences on its own molecule of
DNA (or RNA) (if affects several genes, implies that the site does not code for
protein, but is in a regulatory region)

Question 15

is the lac mRNA stable and what does this mean

Answer 15

no its very unstable so induction can be rapidly reversed

Question 16

how many binding sites does the lac repressor have and what are they for

Answer 16

2, 1 for operator and one for inducer

Question 17

what type of mutations are mutations in lacI gene and why

Answer 17

trans-acting bc they affect expression of all lacZYA

Question 18

what type of mutations are mutations in operator gene and why

Answer 18

cis-acting bc they only affect genes on the contiguous stretch of DNA

Question 19

what is the inducer for the lac repressor

Answer 19

allolactose (changes the shape)

Question 20

what does it mean to be negatively regulated

Answer 20

in absence of induced, expression is blocked (neg controlled) by repressor

Question 21

what is glucose’s effect on the lac operon and why

Answer 21

regulates it positively becuase if you have glucose it’s more favorable to use glucose than lactose

Question 22

how do concentrations of glucose and cAMP relate and why

Answer 22

inversely related due to direct competition between glucose transporter and adenine cyclase for the cofactor

Question 23

how does cAMP affect CRP/lac operon

Answer 23

CAP or CRp is a positively regulator protein activated by cAMP. often needed for RNA pol to initiate transcription at operon. cAMP binds to CRP and activates it. the protein binds to DNA and increases operon transcription efficiency

Question 24

what type of operon is the tryptophan operon

Answer 24

repressible

Question 25

what regulates trp expression

Answer 25

trpR repressor protein and co-repressor

Question 26

what happens when trp is present

Answer 26

transcription starts but stops at trpL (leader)

Question 27

how does trp transcription termination work

Answer 27

leader region has region 1 & 2 which can base pair, same with 3 & 4 and 2 &3. region 4 is followed by a bunch of Us. if 1 &2 and 3 & 4 bind then it forms a transcription stop structure and will stop at L region

Question 28

what are riboswitches

Answer 28

part of an mRNA molecule that bind small molecules, and
control expression of the gene either by regulating translation of transcription