Regulation pt. 1

Question 1

Why is regulation important

Answer 1

Saves energy and space (can’t make all proteins all the time - energetically costly/space), helps adapt to changing conditions, activities of some gene products are detrimental (spore formation)

Question 2

What is the exception to turning genes on and off

Answer 2

housekeeping genes are always expressed - constitutive enzymes (enzymes that metabolize glucose)

Question 3

what is an operon

Answer 3

genes under the same promoter - when it gets turned on, all the genes on operon turn on

Question 4

what do polycistronic mRNAs have multiple of

Answer 4

ribosome binding sites

Question 5

how do regulatory proteins regulate / what can they be

Answer 5

they regulate the target gene by binding the regulatory sequence on the opperator/ can be activators or repressors - can have positive or negative affect

Question 6

why is the inverted repeat symmetry important for regulatory sequences / what happens as the match of the symmetry grows

Answer 6

the regulatory proteins almost always bind as dimers / the closer to a perfect match the higher the affinity

Question 7

what is a ligand

Answer 7

specific low-molecular-weight compound that alters the DNA-binding of the regulator

Question 8

what is allosteric regulation

Answer 8

the ligand changing the shape of the regulatory protein which in turn changes the proteins affinity for DNA

Question 9

what do repressors do / where do they bind / what are the two types of ligands are there

Answer 9

they always block transcription / to the DNA sequence in front of a protein but after the promoter sequence / an inducer or a corepressor

Question 10

how does a corepressor ligand regulate / how does levels of ligand in cell change the repression of a gene

Answer 10

it binds to the repressor which then binds to the DNA and turns off operon / lower levels of the ligand in the cell means that the regulator protein will lose its corepressor and no longer bind to the DNA - leads to expression of the gene

Question 11

how does an inducer ligand regulate

Answer 11

the regulator protein is already bound to DNA - in presence of ligand it loses affinity for DNA and the transcription of the gene is induced

Question 12

what are activators / what do they almost all require

Answer 12

stimulate transcription / almost all require a ligand

Question 13

what is the activator ligand called / where does the activator+ligand complex bind

Answer 13

an inducer / before the promoter of the operon (bends the DNA to contact the RNA polymerase)

Question 14

what does LacZ (beta-glactidase) do

Answer 14

degrades lactose into constituents (saccharides which go into glycolysis & feed bacteria)

Question 15

what is diauxic growth / what kind of growth curve does the regulation of lactose exhibit

Answer 15

two phased growth / diauxic growth (very little lag phase, growth with glucose, lag, growth with lactose, stationary)

Question 16

what does LacY do

Answer 16

imports lactose & protons at the same time (symporter)

Question 17

what does induction mean for lacZ in lactose utilization

Answer 17

it turns the production of beta-galactosidase on only when lactose is present

Question 18

what is the key regulatory component 1 in lactose utilization

Answer 18

LacI - constitutavely expressed

Question 19

what does LacI bind to repress expression of lactose operon / why is it important that the lac operon is never fully off

Answer 19

lacO and lacOi / always up to 10 molecules of lacZ per cell because it allows for the production of allolactase

Question 20

what is allolactase / why is it important for presence of lactose

Answer 20

allolactase is the inducer ligand for lacI / allolactose is made from lactose by lacZ when there are low levels - keeps the operon sensitive to the levels of lactose

Question 21

what does the cyclic AMP receptor protein (cAMP CRP) do

Answer 21

binds to cAMP and activates lactose operon when bacteria are starving

Question 22

what is catabolite repression

Answer 22

the presence of a more favorable catabolite (glucose) prevents the expression of operons that enable catabolism of a second carbohydrate (lactose)

Question 23

what does inducer exclusion do

Answer 23

keeps lactose out of the cell in the presence of glucose due to the phosphorylation of the IIA protein involved with PEP

Question 24

what happens when glucose is not present in the cell

Answer 24

the phosphorylation status of the IIA changes and is now phosphorylated so it cannot inhibit lacY - also produces cAMP from ATP

Question 25

what is feedback inhibition

Answer 25

if end product of pathway is present the pathway will not be turned on

Question 26

what three types of regulation are used for the trp operon

Answer 26

feedback inhibition, transcriptional repression, transcriptional attenutation

Question 27

how does trp itself regulate expression

Answer 27

it binds to the aporepressor that makes the holorepressor (feedback inhibition)

Question 28

what is trpR / how does it prevent the transcription of the operon

Answer 28

the repressor of trp / binds to the corepressor which binds to the operator and prevents transcription

Question 29

what does transcriptional attenuation do for the trp operon

Answer 29

fine tunes the expression of the operon - used in conjunction with repression / functions to halt transcription before structural genes

Question 30

what does the attenuator site do / where is it located

Answer 30

forms two different loop structures that either terminate transcription (3:4) or promote (2:3) / between the transcriptional start site and the first structural gene

Question 31

what does region 1 (leader) do in the attenuator

Answer 31

does nothing except for contain two Trp next to each other - the ribosome stalls here due to the low trp levels as there is no charge on the Trp (allows for the 2:3 loop to form)

Question 32

would you expect transcriptional attenuation (down-regulation of the operon) to work in a eukaryotic cell

Answer 32

no as it requires the robosome to be present on the transcript