Lecture 7 - Four Genetics for Operon Control

Question 1

What does the binding of the lactose repressor protein to the operator do?

Answer 1

Blocks transcription of the lactose operon

Question 2

What kind of feedback system is the binding of the lactose repressor protein to the operator?

Answer 2

Negative feedback system

Question 3

How did Jacob and Monod determine the regulatory mechanism of the lactose operon before the advent of gene cloning and DNA sequencing?

Answer 3

• use of strains of E.coli that had mutants in the lactose operon and its regulatory gene, lacI
• construction of partial diploids (or merodiploids) with mutations in the lactose operon and its regulatory gene, lacI

Question 4

What pumps lactose into the cell?

Answer 4

Permease

Question 5

What does it mean when the E.coli phenotype is constitutive?

Answer 5

that the gene is not regulated

Question 6

What is an example of induction of enzyme synthesis?

Answer 6

the activity of enzymes involved in lactose metabolism

Question 7

What is an example of repression of enzyme synthesis?

Answer 7

The activity of enzymes involved in tryptophan metabolism (when tryptophan is added, enzyme synthesis is dramatically decreased)

Question 8

What happens when ligand binds to the inner oppressor?

Answer 8

it turns off transcription at the tryptophan operon

Question 9

Describe inducible operons and give an example.

Answer 9

• substrate is the effector molecule

- ex. lactose operon: ( lactose -> glucose +galactose)

Question 10

Describe repressible operons and give an example.

Answer 10

• end product of the metabolic pathway is the effector molecule
• ex. tryptophan operon (A -> B -> C -> D -> Trp)

Question 11

What kind of control are the inducible and repressible operons?

Answer 11

negative control

Question 12

What does the ligand do?

Answer 12

Either the substrate (catabolic pathway) or the end-product (anabolic pathway) induces or represses synthesis of the enzymes encoded by the operon

Question 13

What does the regulatory protein (repressor or activator) do when bound to the oprator?

Answer 13

stops or enhances transcriptional initiation of the operon

Question 14

What are the three rules to remember for the 4 types of prokaryotic operon regulation?

Answer 14

1) cell’s DON’T waste energy
2) inducible vs. repressible operons
3) negative vs. positive control

Question 15

For the negative control of operons, what is the regulatory protein and signal molecule and inducible operon and a repressible operon? Give an example for each

Answer 15

• Inducible operon (catabolic pathway): regulatory protein is the repressor, the signal molecule is the precursor or substrate of the catabolic pathway. Ex. Lactose operon
• Repressible operon (anabilic pathway): regulatory protein is the repressor, the signal protein is the end-product of the anabolic pathway. Ex. Tryptophan operon

Question 16

What is the regulatory protein for the inducible and repressible operon under positive control and what are an example of each?

Answer 16

• Regulatory protein: activator
• inducible operon ex. Arabinose operon
• repressible operon ex. there’s a few