6.8.3 lac Operon: The Summary

Question 1

operon

Answer 1

• a unit of function consisting of regulated clusters of genes. An operon provides control of a sequence of
  genes that are related in metabolic activity

Question 2

note

Answer 2

• The lac operon is an inducible operon that controls the transcription of three enzymes that metabolize lactose.
  A wrap-up of its elements follows

Question 3

The lac operon has a strategic design, enabling the cell toefficiently manage transcriptional control of lactose-digesting enzymes:

Answer 3

1. Looking at the picture, you can see that the gene sequences coding for the three enzymes occur adjacent to each other on the DNA strand. The sequences are labeled lacZ, lacY, and lacA on the illustration.
2. The promoter sequence is to the left of the sequences, enabling RNA polymerase to synthesize mRNA in a 5’ to 3’ direction.
3. A genetic sequence to the left of the promoter, called the lacI gene, codes for the repressor protein.
4. When lactose is absent, the repressor protein binds to the operator, a site that lies in between the promoter and the gene sequences of the enzymes.
5. The location of the operator enables the repressor protein to act as a physical block, preventing RNA polymerase from binding to the promoter.
6. When lactose is present, the repressor protein is inhibited and transcription of the enz

Question 4

The operator site for the lac operon is located between the promoter site and the genes coding for the proteins which digest lactose such that

Answer 4

• the repressor protein is able to prevent transcription of the genes for the digestive enzymes from occuring

Question 5

True or false?

The lac operon is an example of negative gene regulation.

Answer 5

• true

Question 6

A mutation in a regulatory gene of an inducible operon stops the gene from producing a functioning repressor. What would be the result?

Answer 6

• The enzymes in the operon will continuously be expressed

Question 7

What is an allosteric site?

Answer 7

• A specific site on an enzyme apart from the active site. Molecules that bind here will change the shape of the active site.

Question 8

_______________ is a piece of DNA that consists of a set of genes with related functions under the same regulatory control.

Answer 8

• An operon

Question 9

True or false?
An inducible operon is a regulatory unit of DNA that is inhibited when a small molecule interacts with a regulatory protein.

Answer 9

• false

Question 10

With regard to the lac operon, the regulatory gene does which of the following:

Answer 10

• Codes for the repressor protein.