chapter 14

Question 1

what does allosteric mean?

Answer 1

regulation of a proteins activity by binding of a small molecule to part of protein different from active site, causing conformational change

Question 2

gene regulation def.

Answer 2

level of gene expression can vary
under different conditions

Question 3

what is the benefit of regulation genes?

Answer 3

encoded proteins or RNAs will
be produced only when required (energetically efficient)

Question 4

what cellular processes is gene regulation important for?

Answer 4

metabolism
response to environmental stress
cell division

Question 5

when can gene regulation happen?

Answer 5

at any point on the pathway of gene expression but often occurs at the start- intiation of transcription (Energetically efficient place to regulate gene expression)

Question 6

organization of lac operon

Answer 6

1. The lacZYA genes
2. The lacI gene
3. DNA elements: CAP site, lac promoter, operator site (lacO)
4. CAP, another regulatory protein, is not shown here

Question 7

lacZYA genes

Answer 7

encode proteins involved in lactose metabolism

Question 8

lacZ

Answer 8

Encodes b-galactosidase
- Enzymatically cleaves lactose and lactose analogs
- converts lactose to allolactose (an isomer, important for signaling)

Question 9

lacY

Answer 9

Encodes lactose permease
- Membrane protein required for transport of lactose and analogs

Question 10

lacA

Answer 10

Encodes galactoside transacetylase
- Covalently modifies lactose and analogs

Question 11

lacI gene ( makes lac repressor)

Answer 11

encodes a regulatory protein
- in the start so not part of lac operon bc it has its own promoter

• expressed at low levels
• encodes lac repressor
  functions as a tetramer and only a small amount is needed to repress lac operon

Question 12

regulation of lac operon expression by lactose relies on what

Answer 12

• lacl / lac repressor protein
• lacO (operator) DNA elements

Question 13

in the absence of lactose, lac repressor___ expression of lac operon by ____ to lacO

Answer 13

inhibits the expression of lac operon by binding to the lacO

Question 14

enzyme beta-galactosidase carries out what reaction(s) in E. coli bacteria?

Answer 14

1. Breaks down lactose into
   glucose and galactose
2. Converts lactose into
   allolactose

Question 15

are lac ZYA genes expressed when there is no lactose?

Answer 15

NO … 2 explanations: evolutionary vs mechanistic

evolutionary- energetically inefficient to make these proteins when there’s no lactose

mechanistic- The lacI repressor protein binds to lacO, which keeps RNA polymerase from transcribing lacZYA.

Question 16

when there is lactose how is expression of lacZYA turned on?

Answer 16

Allolactose binds to the lacI
repressor protein so it no longer
binds to lacO, so RNA polymerase
can transcribe lacZYA

Question 17

whats hte effect of the following mutations on expression of lacZ in presence and absence of lactose?
- mutation in lac l that no functional repressor protein is made

Answer 17

lacZ will be expressed whether lactose is present or not

Question 18

if theres a mutation in lacO that makes lacl not bind to it (lacO^c mutation), what will the effect on lacZ expression be

Answer 18

lacZ will be expressed whether lactose is present or not

Question 19

if there is a mutation in lacl so that the protein cannot bind to allolactose but the rest it unaffected, what will be the effect on lacZ expression be

Answer 19

lacZ will not be express whether lactose is present or not
because lacl repressor will bind to lacO whether or not lactose is present and will shut off transcription of lacZYA in all conditions

Question 20

is allolactose/lactose is present will operon be expressed?

Answer 20

yes
allolactose is made from lactose

Question 21

why do cells prefer to use glucose instead of lactose?

Answer 21

glucose is metabolizes more easily than lactose

Question 22

breakdown of glucose for cells to get energy from it

Answer 22

cells get ATP from glucose and break it by glycolysis / citric acid cycle and oxidative phosphorylation.

Question 23

breakdown of lactose to yield energy for cells to use

Answer 23

its broken down into glucose and galactose then thats converted to glucose then it can be broken down more to make ATP

Question 24

will lacz be expressed at high (on) or low level (off) when glucose + lactose are both absent?

Answer 24

off / low levels since there is no reason to make lacZ bc theres no lactose for lacZ to breakdown

Question 25

will lacz be expressed at high (on) or low level (off) when glucose is absent + lactose is present?

Answer 25

on / high levels since only lactose is present so it needs lacZ to get energy

Question 26

will lacz be expressed at high (on) or low level (off) when glucose is present + lactose is absent?

Answer 26

off /low level since theres no lactose so no reason to make lacZ

Question 27

will lacz be expressed at high (on) or low level (off) when both glucose + lactose are present?

Answer 27

off /low levels since cells prefer to use glucose over lactose

Question 28

regulation of lac operon expression by glucose with low glucose

Answer 28

cAMP is high in concentration CAP binds to cAMP and binds to the CAP site next to promoter - helps RNA polymerase bind to promoter and leads to high rate of transcription (if no repressor is bound to operator)

Question 29

regulation of lac operon expression by glucose with high glucose

Answer 29

cAMP is low - Without cAMP, CAP cannot bind the CAP site in front of the lac operon - Without CAP’s help, RNA polymerase binds only weakly to the promoter - Operon expression is low

Question 30

cAMP

Answer 30

small molecule, cyclic AMP

Question 31

CAP

Answer 31

catabolite activator protein

Question 32

What’s the function of the genes in the lac operon in E. coli bacteria?

Answer 32

To encode proteins that take up and metabolize lactose as a source of energy

Question 33

When glucose is present, why can the lac operon be expressed at only a low level even if lactose is present?

Answer 33

Because cells prefer to use glucose instead of lactose + Because CAP does not bind to the CAP site

Question 34

high [lactose], high [glucose]

Answer 34

cAMP low (bc high glucose) allolactose high - cap doesnt bind to cap site bc not bound to cAMP - lacl repressor doesnt bind to lacO bc bound to allolactose - RNA poly. is only active at low levels bc no CAP bound to CAP site so it will transcribe - lazZYA is expressed at low levels

Question 35

high glucose = low or high cAMP

Answer 35

low!

Question 36

no [lactose], high [glucose]

Answer 36

cAMP is low (bc glucose is high) allolactose low - CAP doesnt bind to CAP site because it is not bound to cAMP -lacl repressor binds to lacO bc not bound to allolactose -RNA poly. is inactive because no CAP bound to CAP site and lacl binds to lacO -lacZYA not expressed lacl binds to lacO blocking RNA poly. + CAP doesnt bind to CAP site, reducing RNA poly. activity

Question 37

high [lactose], low [glucose]

Answer 37

cAMP is high allolactose is high - CAP binds to CAP site because bound to cAMP - lacl repressor does not bind to lacO because it is bound to allolactose - RNA poly. is active (high level of transcription) bc CAP IS bound to CAP site + lacl not bound to lacO - lacZYA is expressed at high levels

Question 38

no lactose, low [glucose]

Answer 38

cAMP is high allolactose is low -CAP binds to CAP site bc bound to cAMP - lacl repressor binds to lacO bc not bound to allolactose -RNA poly. is inactive bc lacl binds to lacO - lacZYA is not expressed low level of allolactose allow lac repressor to shut off expression by binding to lacO even though CAP binds to CAP site

Question 39

What would be the effect on expression of the lac operon of a loss-of-function mutation in the gene for CAP?

Answer 39

lac operon would not be expressed at a high level regardless of what sugars were present

Question 40

why is cap necessary?

Answer 40

for a high level pf expression of lac operon under any condition- it helps RNA poly. bind to promoter