Ch:18 Regulation of Gene Expression: The Operon

Question 1

The ____ is found in bacteria and is an important model that consist of a gene cluster.

Answer 1

Operon

Question 2

What are the 3 parts of a Lac-operon?

Answer 2

Lac-operon (think lactose)

Operator: “the on-off switch” binding site available for a repressor protein that can prevent transcription.

Promoter: the site where RNA polymerase attaches

Question 3

When is the lac-operon turned on?

Answer 3

When there is lactose present

when the lac-operon is off there will be no lactose-metabolizing enzymes

Question 4

When lactose is present… it needs to be metabolized. Allolactose, an isomer of lactose formed in reasonable amounts acts as an ____. An ___ binds to the repressor and distorts its shape… this altered conformational change will prevent the repressor from binding to the operator. The promoter site is now exposed to RNA polymerase and transcription can begin.

Answer 4

Inducer

Question 5

Structural genes are in the ____ region, while the operator and repressor are in the ________ region.

Answer 5

Structural genes are in the coding region

Operator and repressor are in the regulatory regions

Question 6

When does E. coli use lactose as an energy source?

Answer 6

When lactose is present and glucose levels are low

Question 7

The Lac operon is under dual control:

Answer 7

1. Negative control by the repressor protein
2. Positive control by the CAP
   - When glucose levels are low, cyclic AMP accumulates and binds to CAP… once bound, CAP now has the proper shape to bind to the promoter… this aids in the attachment of RNA polymerase to the promoter

Question 8

What is the difference between the lac-operon and the trp-operon?

Answer 8

lac-operon is catabolic and the trp-operon is anabolic

Question 9

Histones are _____ allowing for less tightly packing of chromatin, hence allowing for better transcription.

Answer 9

acetylated

Histone acetylation promotes transcription

Question 10

DNA methylation: When CH3 groups are added, _____ packing occurs, thus we can see a reduction in gene expression.

Answer 10

Tighter packaging

In other words, inactivated genes are usually heavily methylated, and certain genes are activated by the removal of the CH3 group called demethylation.

Question 11

What 2 things do miRNA and siRNA molecules do when they bind to mRNA?

Answer 11

1. Degrade mRNA

2. Bind to mRNA and block translation