Chapter 16

Question 1

Regulated Genes

Answer 1

Gene activity is only turned on when needed

Question 2

Constitutive genes

Answer 2

genes are always active

Question 3

Inducer

Answer 3

regulatory substance that brings about gene induction

Question 4

what is an operon

Answer 4

a cluster of genes that share a common operator, promoter, and are transcribed onto a single polycistronic mRNA

Question 5

Where does the RNA Pol bind

Answer 5

Promoter

Question 6

sign for promoter

Answer 6

lacI+

Question 7

What does lacI+ do?

Answer 7

produces the Lac repressor

Question 8

What does the Lac Repressor do?

Answer 8

negatively controls expression of the Lac operon by binding to the operator

Question 9

DNA binding site for lac repressor

Answer 9

lacO+

Question 10

beta- galactosidase breaks down

Answer 10

lactose into glucose and galactose

Question 11

beta-galactosidase catalyzes

Answer 11

isomerization of lactose to allolactose

Question 12

lacZ+ is

Answer 12

beta galactosidase

Question 13

lacY+ is

Answer 13

lactose permease

Question 14

Where is lactose permease found

Answer 14

the cell membrane

Question 15

What does lactose permease do

Answer 15

actively transports lactose into the cell

Question 16

lacA+ is

Answer 16

Transacetylase

Question 17

Transacetylase is responsible for

Answer 17

transferring acetyl group from acetyl-coA to beta-galactosidase

Question 18

structural genes that produce genes for lactose processing

Answer 18

• lacZ+
• lacY+
• lacA+

Question 19

What protein does the operator code for

Answer 19

does not code for a protein, is a site for lac repressor to bind

Question 20

What does the lac repressor inhibit

Answer 20

it prevents RNA pol from coding for the genes encoded for lactose metabolism

Question 21

How is the lac repressor transcribed

Answer 21

constitutively

Question 22

How does lac repressor prevent RNA pol from binding

Answer 22

the region where the repressor binds overlaps the RNA pol binding site

Question 23

why does Leaky Expression occur

Answer 23

occurs due to repressor binding and letting go repeatedly

Question 24

leaky expression

Answer 24

it causes a few of the structural enzymes to be produced even in the absence of lactose

Question 25

Why is leaky expression important (Permease)

Answer 25

Permease production allows the initial transport of lactose into the cell

Question 26

Why is leaky expression important (conversion)

Answer 26

beta- galactosidase causes the initial conversion of allolactose which acts as an inducer

Question 27

What is the inducer

Answer 27

allolactose

Question 28

Where does allolactose come from

Answer 28

it is synthesized from lactose by B gal

Question 29

Synthesis of lactose products (by B-gal)

Answer 29

1) galactose 2) Glucose 3) Allolactose

Question 30

order of structural enzymes made

Answer 30

1) B-Gal 2) Permease 3) Transacetylase

Question 31

Why is glucose a better carbon source than lactose.

Answer 31

B-gal is used to break down lactose into glucose, so it consumes more energy to than glucose would.

Question 32

when is operon turned on

Answer 32

lactose is present, but no glucose

Question 33

When is lac operon turned off

Answer 33

when glucose is present

Question 34

What binds to the CAP site and recruits RNA polymerase to operon

Answer 34

Catabolite activator protein (CAP)-cAMP complex

Question 35

what regulates level of cAMP

Answer 35

glucose

Question 36

glucose effect

Answer 36

turns off lac operon when glucose is present

Question 37

relationship between glucose levels and cAMP levels

Answer 37

as glucose decreases, cAMP increases

Question 38

What is catabolite expression

Answer 38

the direct regulation of cAMP by glucose

Question 39

positive control

Answer 39

CAP allows transcription.

Question 40

negative control

Answer 40

lac repressor blocks transcription

Question 41

what does Z^(-) mean?

Answer 41

B-Gal mutant non functional gene

Question 42

what does O^c mean

Answer 42

constitutive operator mutation

Question 43

Cis dominant

Answer 43

a gene or sequence that controls genes only located on same DNA molecule

Question 44

trans dominant

Answer 44

interaction with genes from other DNA molecule

Question 45

what does constitutive operator cause

Answer 45

it prevents the lac repressor from binding, constitutive synthesis occurs

Question 46

is lacO^c cis dominant?

Answer 46

YES, only affects genes downstream on same DNA molecule

Question 47

Effect of lacI^(-)

Answer 47

Mutant repressor cannot bind to operator, constitutive synthesis occurs

Question 48

is lacI+ gene trans dominant to lacI- ?

Answer 48

yes, can override a nonfunctional lacI gene on a different strand

Question 49

effect of lacI^s

Answer 49

no production of lac enzymes in presence or absence of inducer, which means inducer has no effect on lacI+

Question 50

Is lacI^s cis or trans dominant?

Answer 50

Trans, because the Is on the bottom segment is producing a super repressor that binds to the operon on the top segment

Question 51

what does lacI^d- do

Answer 51

it encodes dominant subunits which will make a bad repressor that loses its ability to repress the operon

Question 52

effect of Plac-

Answer 52

nonfunctional promoter that cannot make the 3 structural enzymes

Question 53

is Plac- cis or trans dominant?

Answer 53

It is cis because it only affects the genes in it's own DNA strand