Lecture 7: Bacterial Genes File

Question 1

What is glucose ?

Answer 1

Monosaccharide - can enter E.coli metabolism directly

Question 2

What is Lactose ?

Answer 2

Disaccharide (made up of glucose + galactose) - must be split to enter E.coli metabolism

Question 3

If glucose is present …..

Answer 3

The lac operon is not expressed (OFF)

Question 4

If glucose is not present and lactose is not present ….

Answer 4

The lac operon is not expressed (OFF)

Question 5

If glucose is not present but lactose is present?

Answer 5

The lac operon is expressed (ON)

Question 6

what is lac operon made up of ?

Answer 6

Three genes closely linked on bacterial chromosome (lacZ,lacY and lacA)

Question 7

LacZ= ?

Answer 7

encodes b-galactosidase - catalyses conversion of disaccharide lactose into monosaccahride glucose +galactose

Question 8

Lac Y = ?

Answer 8

encodes lactose permease = membrane bound protein that facilitates uptake of lactose into cell

Question 9

LacA = ?

Answer 9

Nobody knows lol

Question 10

What is a gene promoter ?

Answer 10

DNA site where RNA polymerase binds before transcription starts

Question 11

what is the 4th lac gene ?

Answer 11

Lacl = always expressed, makes a repressor that binds to the operator, which blocks RNA polymerase so theres no transcription

Question 12

why do mutations in Lac genes not affect downstream genes ?

Answer 12

They each have their own translational start site

Question 13

What is the Lac Z mutant ?

Answer 13

Cannot make b-galactosidase , lactose enters cell but cannot be used

Question 14

What is the Lac Y mutant ?

Answer 14

cannot make permease, cannot get lactose into cell

Question 15

What is the Lac A mutant ?

Answer 15

Lactose can enter but cannot be used (same as lac Z mutant)

Question 16

What is the Lac l mutant ?

Answer 16

Makes no repressor, lac operon is always expressed (ON)

Question 17

What is the Lac Is (super-repressor) mutant ?

Answer 17

when lacl makes mutant repressor which cannot bind to lactose (lac operon always OFF)

Question 18

what is Lac Oc mutant ?

Answer 18

Operator site is mutant and doesnt recognise repressor (Repressor doesnt bind, lac operon always ON)

Question 19

When staining for Lac Z, what are the colours ?

Answer 19

LacZ+ = blue 
LacZ- = white

Question 20

When staining for Lac Z, what does it grow on ?

Answer 20

Bacterial Xgal

Question 21

What are the steps for LacZ reporter genes ?

Answer 21

1. Take control region of gene of interest
2. splice it to the coding region
3. make transgenic fly carrying reporter gene