Regulation of gene expression prokaryotes - lecture 2

Question 1

Operon definition

Answer 1

A group of bacterial structural genes that are transcribed together ( i.e with including the promoter)

Question 2

Lactose metabolism in E.Coli ; what enzyme converts Lactose into Allolactose

Answer 2

Beta - Galactosidase

Question 3

What are the products when Beta - Galactosidase acts on lactose/allolactose ?

Answer 3

Galactose and Glucose

Question 4

What is the lac operon an example of?

Answer 4

Negative inducible operon

Question 5

What happens in the absence of lactose to the lac operon?

Answer 5

The regulator protein ( a repressor) binds to the operator and inhibits transcription

Question 6

What happens in the presence of lactose to the lac operon?

Answer 6

• Some lactose converted to allolactose
• Allolactose binds to the regulator protein, making it inactive
• Regulator cannot bind to the operator, therefore genes can be transcribed and translated

Question 7

Definition of an inducible operon

Answer 7

Transcription is usually off and needs to be turned on

Question 8

Definition of a repressible operon

Answer 8

Transcription is normally on and needs to be turned off

Question 9

what happens when a substrate is added to a Negative inducible operon ?

Answer 9

The substrate makes the repressor inactive - transcription turned on

Question 10

what happens when a substrate is added to a positive inducible operon ?

Answer 10

The substrate makes the the activator active, transcription turned on

Question 11

What happens when a product is added to Negative repressible operon?

Answer 11

Th product binds to and makes the repressor active, transcription turned off

Question 12

What happens when a product is added to positive repressible operon?

Answer 12

The product binds and makes the activator inactive , transcription turned off

Question 13

What does antisense RNA do in regulating gene expression?

Answer 13

Bind to sequences of mRNA and inhibiting translation

Question 14

What does the ompF protein encode in bacteria?

Answer 14

codes for an outermsmbrane protein that functions as a channel for diffusion of water and ions

Question 15

What happens when osmolarity is low in a bacterial cell?

Answer 15

The ompf mRNA is translated to produce OmpF protein , letting water in

Question 16

What happens when osmolarity is high in a bacterial cell?

Answer 16

The micF gene is activated which produces micF RNA.
micF RNA pairs with the 5 prime end of the ompF RNA ,
blocking the ribosome binding site for the ompF gene. No protein produced

Question 17

What is a riboswitch?

Answer 17

affect gene expression by influencing the formation of the mRNA structure

Question 18

Action of a riboswitch

Answer 18

Regulatory protein binds the riboswitch and stabilise structure. Masks the ribosomes- binding site. No translation

Question 19

Ribozyme defintion

Answer 19

RNA enzyme that catalyses a chemical reaction

Question 20

What bacteria is the lac operon present in?

Answer 20

E.coli