Gene Regulation in bacteria part 2

Question 1

Which hypothesis is right?

Answer 1

Hypothesis 1 which states the lacl si a repressor & lacl^- mutant is an inactive repressor to yield a constitutive operon

Question 2

The ________ strain is partial diploid

Answer 2

Merozygote

Question 3

The ______ strain is hemizygous because its monoploid for lacl & monoploid for operon

Answer 3

Mutant strain

Question 4

The _______ is heterozygous because its diploid for lacl & diploid for operon (it has lacl^- on the chromosome & lacl⁺ on the plasmid)

Answer 4

Merozygote

Question 5

In _________ the lacl^- is an activator repressor & the lacl⁺ on the plasmid is an active repressor which inhibits both lac operons

Answer 5

Hypothesis 1

Question 6

In hypothesis 1 the ______ is on the chromosome where it has no effect (l.o.f.)

Answer 6

lacl^-

Question 7

In hypothesis 2 where the ______ is a constitutive activator the lacl^- is on the chromosome (g.o.f.) (activated operon)

Answer 7

lacl^-

Question 8

What are the steps for testing the two hypotheses?

Answer 8

1. Grow mutant & merozygote strains separately
2. Each strain is divided into two test tube (4 test tubes)
3. One of the two test tubes (tubes 2 &4) gets lactose added
4. Incubation
5. The cells are lyse with sonicator
6. The substrate B-ONPG is added where if B-galaclactose is present it will cut it down in the test tube & the tube will turn yellow
7. Incubate
8. Measure the yellow color produced

Question 9

What are the results for the mutant strain?

Answer 9

For the mutant strain the lacl^- is constitutive where the operon is on without lactose & adding lactose has no effect where the operon stays on

Question 10

What are the results for the merozygote strain ?

Answer 10

The merozygote strain is het. where the lacl⁺ is on the plasmid (lacl⁺ dominated lacl^- therefore lacl^- is l.o.f.) the operon is off without lactose (consistent with hypothesis 1)

Question 11

For the ________ strain the lacl⁺ on the plasmid is inactivated by allolactose where operon is turn on by 200% (consistent with hypothesis 1)

Answer 11

merozygote

Question 12

Trans-effect

Answer 12

Form of regulation that occurs between two DNA sequences that aren’t adjacent (on the same molecule) (ex. lac repressor on the lac operon)

Question 13

The lac repressor is a __________ factor (regulates operon)

Answer 13

Trans-acting factor

Question 14

Cis-acting factor

Answer 14

A DNA segment that is adjacent (on the same molecule) to the gene it regulates (ex. lac operon is a cis-acting factor)

Question 15

A _________ is caused by genes that encoded regulatory proteins

Answer 15

Trans-effect

Question 16

________ is caused by DNA sequences that are bound by regulatory proteins

Answer 16

Cis-effect

Question 17

The ______ mutant is a binding site for lacl so its a cis factors as well

Answer 17

lacO

Question 18

A mutation in the ________ factor can be rescued by introducing a second gene with normal functions ( a second wild type gene that is het.)

Answer 18

Trans-acting factor

Question 19

A mutation in the _________ factor can’t be reused by introducing another cis-acting factor with normal function (can’t be rescued by second wild type factor that is het.)

Answer 19

Cis-acting factor

Question 20

Another way that the lac operon can be regulated is by _________ which is influenced by the presence of glucose where it represses the lac operon

Answer 20

Catabolite repression

Question 21

In __________ when glucose is gone then the operon is turned on

Answer 21

Catabolite repression

Question 22

In catalbolite repression glucose isn’t the effector molecule that binds to the regulatory protein but _________ is

Answer 22

Cyclic-AMP (cAMP)

Question 23

lac operon is regulated _______ & _________

Answer 23

Repressor lacl & activator called CAP

Question 24

For max transcription repressors are ______ & activators are ______

Answer 24

Off, On

Question 25

What are the 3 operator sites in lac operon?

Answer 25

1. O₁ - the operator site is slightly downstream from the promoter
2. O₂ - is located farther downstream past the lacZ coding sequence
3. O₃ - is located slightly before from the promoter

Question 26

So the lac operon can bind to O₁ & O₂ or to O₁ & O₃ but never to ________

Answer 26

O₂ & O₃

Question 27

When the lac repressor binds to two operator site a ______ must formed

Answer 27

Loop

Question 28

The lac repressor is a ______ where it has binding sites for each operator site (like dimer such as O₃)

Answer 28

tetramer

Question 29

Because each dimer in the tetramer recognizes a single promoter site, when two dimers are used (like O₁ & O₃) the tetramer requires that the two operator site are closer together and that is why a ______ forms in DNA

Answer 29

Loop

Question 30

The loop inhibits RNA polymerase from passing the ____ site & transcribing the operon

Answer 30

O₁