Chapter 24 - The Operon

Question 1

Genes with related function are clustered together under the control of a single

Answer 1

promoter

Question 2

multiple genes transcribed on a single mRNA are called

Answer 2

polycistronic

Question 3

operon

Answer 3

Group of bacterial structural genes transcribed together
Also contains a promoter and an operator

Question 4

structural genes

Answer 4

Multiple genes transcribed into one mRNA
Under control of one promoter

Question 5

regulator gene

Answer 5

Under control of separate promoter
Transcribed and translated into regulator protein
Influences transcription of structural genes

Question 6

in a negative operon, the regulator protein is a

Answer 6

repressor

Question 7

in a negative operon the Trans-acting repressor binds to the cis-acting operator and

Answer 7

reduces the rate of transcription

Question 8

in a positive operon the regulator protein is

Answer 8

an activator

Question 9

in a positive operon the Trans-acting activator binds to a cis-acting element to …

Answer 9

activate transcription

Question 10

inducible operons

Answer 10

Transcription is off by default and must be turned on (induced)

Question 11

repressible operons

Answer 11

Transcription is on by default and must be turned off (repressed)

Question 12

four types of operons

Answer 12

Negative inducible
Negative repressible
Positive inducible
Positive repressible

Question 13

what kind of operon is the lac operon

Answer 13

negative inducible

Question 14

what is the inducer in the lac operon

Answer 14

allolactose

Question 15

lacI

Answer 15

repressor

Question 16

lacZ

Answer 16

Beta-galactosidase

Question 17

lacA

Answer 17

transacytylase

Question 18

lacY

Answer 18

permease

Question 19

Properties of lacI transcription

Answer 19

Unregulated gene with a low level of constitutive expression
Transcribed into a mRNA with almost no 5’-UTR

Question 20

lacOc

Answer 20

constitutive cis-acting mutation

Question 21

lacI-

Answer 21

constitutive trans-acting mutation

Question 22

lacIs

Answer 22

uninducible trans-acting mutation

Question 23

lacI-d

Answer 23

is a dominant negative trans-mutation when found in a heterozygous merozygote
One mutant subunit in the tetramer will block repressor action

Question 24

lac repressor

Answer 24

The repressor binds to an inverted repeat in the operator
Binds more tightly to the upstream side of the repeat
Within the major groove of DNA
Inducer binding changes the structure of the repressor core so that it can no longer bind into the minor groove

Question 25

three lac operators

Answer 25

lacO1 lacO2 lacO3

Question 26

lacO1

Answer 26

is the classic operator at the promoter-lacZ boundary

Question 27

lacO2

Answer 27

is 410 bp downstream of the transcription start site within lacZ

Question 28

lacO3

Answer 28

is 88 bp upstream of lacO1 within lacI

Question 29

the repressor has a higher affinity for which operator

Answer 29

O1

Question 30

each dimer on the repressor can bind to

Answer 30

a palindromic operator sequence

Question 31

When the repressor binds to O1-O2 or O1-O3, it induces a

Answer 31

loop into the DNA between the two binding sites

Question 32

Repressor binding ... RNAP binding to the promoter

Answer 32

enhances

Question 33

Active repressor has ... affinity for random DNA

Answer 33

low

Question 34

Almost all active repressor is bound to either

Answer 34

low-affinity sites in the genome or the operator

Question 35

Less than what percent of active repressor is free in cell

Answer 35

0.01%

Question 36

The difference in affinities between the low-affinity and high-affinity sites is large enough that

Answer 36

active repressor is usually bound to the operator

Question 37

Operator is occupied by repressor ...% of the time

Answer 37

96%

Question 38

what level of transcription allows cell to always be poised for operon induction

Answer 38

basal

Question 39

When the repressor is inactivated by inducer, affinity of binding to the operator is

Answer 39

reduced

Question 40

Repressor tetramers are ... on DNA

Answer 40

stored

Question 41

What are the general parameters that influence the ability of a regulator protein to bind to a specific site?

Answer 41

1. The size of the genome dilutes the ability of a protein to bind a specific target 2. The specificity of a protein counters the effect of genome size 3. The amount of protein that is required for effective binding to a specific site increases with increased genome size 4. Amount of protein must be in excess of total number of binding sites