Lecture 11

Question 1

Constitutive genes

Answer 1

Housekeeping genes that are expressed continuously by the cell

Question 2

Inducible genes

Answer 2

Genes that code for inducible enzymes

Question 3

Which takes fewer steps to metabolize to obtain energy, glucose or lactose?

Answer 3

Glucose b/c lactose needs to break its bond

Question 4

Do you think E.coli prefers to metabolize lactose, glucose, or both?

Answer 4

Glucose b/c lactose takes more energy to break down
-Glucose directly does glycolysis

Question 5

Is bacteria polycistronic or monsocistronic

Answer 5

Polycistronic

Question 6

True or false: the mRNA in eukaryotes is polycistronic

Answer 6

False
Monocistronic

Question 7

Where does RNA polymerase bind?

Answer 7

Promoter

Question 8

In the presence of lactose where does the repressor bind?

Answer 8

It does not bind
-if lactose is present then allolactose is also present
-allolactose–>binds to repressor so repressor will not bind to promoter

Question 9

How does the lac operon prevent RNA polymerase from accessing promoter?

Answer 9

Lac repressor is made from Lacl gene
-repressor binds to the promoter and bends the DNA strand
-Bent DNA strand–>prevents RNA pol from binding
-DNA strand is straight when repressor is off

Question 10

Diauxic growth

Answer 10

-uses one carbon source over another (glucose over lactose)

Question 11

Why is there a lag/plateau in growth curve

Answer 11

Metabolic pathway needs to switch/change from glucose to lactose which takes time

Question 12

True or false: CAP is active without cAMP

Answer 12

False
CAP is only active when bound to cAMP

Question 13

What regulates cAMP?

Answer 13

cAMP levels depend on phosphoenolpyruvate (PE-P) and the sugar phosphotransferase system
-High glucose levels: glycolysis will occur and PEP turns into pyruvate, no cAMP is made
-Low/no glucose: Phosphate activates adenylyl Cyclase, cAMP is made

Question 14

Is cAMP synthesized when there is little/no glucose or a lot of glucose

Answer 14

-Little/no glucose
-PE-P transfers phosphoric group to AC (adenyl cyclase)
-cAMP is synthesized

Question 15

What happens to cAMP and CAP when there is high glucose

Answer 15

CAP is inactive because there is no/low production of cAMP

Question 16

In low/no glucose CAP is?

Answer 16

Active

Question 17

In high glucose CAP is?

Answer 17

Inactive

Question 18

What happens to lac operon when there is HIGH glucose and NO lactose

Answer 18

-Repressor binds–>b/c no allolactose
-CAP is not active b/c cAMP is not made
-No gene expression–>b/c RNA pol cannot bind since DNA is bent

Question 19

What happens to lac operon when there is LOW glucose and NO lactose

Answer 19

-Repressor binds–>b/c no allolactose
-cAMP activates CAP–>b/c glucose levels are low
-No gene expression–>b/c RNA pol cannot bind since DNA is bent

Question 20

What happens to lac operon when there is HIGH glucose and LACTOSE

Answer 20

-allolactose IS present–>prevents repressor from binding to promoter
-DNA is no longer bent, RNA pol CAN bind
-Low level/no cAMP b/c high glucose–> does not activate CAP
-Low level of gene expression

Question 21

What happens to lac operon when there is LOW glucose and LACTOSE

Answer 21

-allolactose IS present–>prevents repressor from binding to promoter
-DNA is no longer bent, RNA pol CAN bind
-cAMP activates CAP b/c low glucose–>CAP helps RNA pol bind
-High level of gene expression

Question 22

True or False: When CAP is active RNA polymerase cannot bind efficiently to the promoter

Answer 22

False
-When CAP is active RNA pol can bind efficiently to promoter b/c it bends DNA in the correct formation

Question 23

How is the Lac operon induced first/ Where is allolactose coming from at the beginning?

Answer 23

-Leaky promoter: RNA pol binds & falls off–>overtime produces allolactose
-When there is no lactose–> 10 molecules of allolactose are produced per cell , overtime it accumulates

Question 24

What does LacZ gene make

Answer 24

B-galactosidase

Question 25

What does LacY gene encode

Answer 25

lactose permease

Question 26

What does lacA encode

Answer 26

galactoside transcetylase

Question 27

What does lacl endode

Answer 27

represser genes

Question 28

Are lacl and lacZ, lacY, and lacA under the same promoter

Answer 28

No
Lacl has its own promoter
-LacZ, lacY, and lacA are under the same promoter

Question 29

The lacl gene is a constitutive gene, what does this mean?

Answer 29

The repressor is always on

Question 30

How does allolactose work?

Answer 30

-binds to repressor
-causes conformational change to repressor
-repressor can longer bind to promoter