lecture 16- gene expression regulation: bacteria

Question 1

where in central dogma is gene expression most commonly regulated?

Answer 1

at step 1- transcription initiation
most energy efficient

Question 2

what steps can gene expression be regulated at?

Answer 2

transcription initiation, RNA processing, RNA stability, protein synthesis, modification, transport, and degradation

Question 3

gene regulation is important to control ___

Answer 3

diseases

Question 4

sigma factors can recognize diff sequences- specificity of sigma depends on sequence

Answer 4

higher affinity –> higher efficiency of transcription

Question 5

if E. coli is in high temps, bacteria survives by doing what?

Answer 5

changing expression of their genes
at 42 C: increase sigma 32 levels - affinity for genes related to heat-shock proteins
at 46 C: 30% of all proteins are heat-shock proteins
at 50 C: sigma 70 inactivated, high levels of sigma 32
at 57 C: RNAP core is inactivated

Question 6

activators and repressors are also called ___

Answer 6

transcription factors

Question 7

activators and repressors control ___

Answer 7

RNA polymerase function at promoter

Question 8

if there’s a repressor in promoter…

Answer 8

RNA polymerase cannot bind

Question 9

if there’s an activator in promoter…

Answer 9

interacts with both RNA polymerase and DNA to activate transcription

Question 10

name cis-acting elements

Answer 10

promoter, operator, activator-binding site, UP element

Question 11

name trans-acting elements

Answer 11

RNAP, repressor, activator

Question 12

transcription regulation is either positive or negative…

Answer 12

• negative control: repressor binds in promoter region and turns off or decreases expression of gene
• positive control: activator binds next to promoter region and recruits RNAP to the site

Question 13

TF’s can function by DNA ___…

Answer 13

DNA looping
- if regulatory binding site is far from promoter, DNA looping can bring them close together
- lac repressor located far from promoter, so DNA loops, bringing repressor to promoter

Question 14

describe how regulators often work together for signal integration

Answer 14

control of a gene by multiple regulators in response to more than one environmental signal
- related set of genes regulated together… in an operon, genes transcribed as a unit together by one promoter –> polycistronic mRNA to produce diff proteins
- operon lac produces proteins involving in making lactose

Question 15

do bacteria prefer glucose or lactose

Answer 15

glucose
lactose genes are under control of an activator protein needed for transcription of lac operon genes, even in absence of lac repressor

Question 16

describe the 3 scenariors: glucose, no lactose
no glucose, lactose
glucose and lactose

Answer 16

1- glucose present, lactose absent — operon lac turned off, lac repressor binds to operator (inside promoter)

2- no glucose, lactose present — use lactose as source for energy — lac operon activated (repressor dissociates & activator binds)

3- glucose and lactose present — bacteria use glucose as primary source, allolactose makes repressor dissociate from promoter, RNA polymerase binds but level of lac mRNA is very low (nonfunctional activator)