Ch.14: Gene Regulation In Bacteria

Question 1

When does the regulation of gene expression occur?

Answer 1

At the level of transcription, translation, or posttranslationally after translation

Question 2

Transcription

Answer 2

Genetic regulatory proteins, such as activators or oppressors; prevent make of RNA

Question 3

Translation

Answer 3

Translational repressor proteins; prevent ribosome from making RNA

Question 4

What does transcriptional regulation involve?

Answer 4

two main types of regulatory proteins:
Repressors - Bind downstream to DNA (promoter) and inhibit transcription (negative control)
Activators- Bind upstream to DNA and increase transcription (positive control)

Question 5

Small Effector Molecules

Answer 5

Inducers- increase transcription , genes that are regulated by these are termed inducible
Corepressors- bind to repressors and cause them to bind to DNA Inhibitors- bind to activators and prevent them from binding to DNA, Genes that are regulated in this manner are termed repressible

Question 6

How do you know when lac operon is on or off?

Answer 6

Lac operon off: When the cell has other sugars available as carbon sources, such as glucose or glycerol
lac operon on: When the cell only has lactose available as a carbon source

Question 7

What are the 3 DNA binding sites in the lac operon?

Answer 7

CAP binding site, lac
promoter, lac (O1) operator

Question 8

What are the 3 proteins that are involved in the regulation of transcription of the lac operon that bind to 3 different sites on DNA

Answer 8

• RNA polymerase binds to the promoter.
• CAP* but not CAP protein binds to the CAP binding site.
• Lac repressor (LacI) binds to the main lac operator (O1) and either the auxiliary lac operators (O2 or O3)

Question 9

How does the lac operon function (three main components)

Answer 9

control via sugar metabolism, via Lacl - lac repressor, and via the stem loop structure of the operator

Question 10

What are Cis-acting elements and trans-acting factors?

Answer 10

Trans-effect or trans-acting factor:
Genetic regulation that can occur even though DNA segments are not physically adjacent
ex. The action of the Lac repressor on the lac operon

Cis-effect or cis-acting element:
A DNA sequence that must be adjacent to the gene(s) it regulates
ex. lac operator binding site

Question 11

What happens when tryptophan levels are low in the cell? What happens when tryptophan levels are high in the cell?

Answer 11

When low ,the trp operon is on so more tryptophan can be made and does not bind to the trp repressor protein, which prevents the repressor protein from binding to the operator site and prevents attenuation and transcription occur

When high, the trp operon is off so no more tryptophan can be made and acts as a corepressor that binds to the trp repressor protein. This causes attenuation and transcription is prevented; The tryptophan-trp repressor complex then binds to
the operator site to inhibit transcription.

Question 12

What happens when attenuation occurs?

Answer 12

its a second method that can turn the trp operon off; the RNA is transcribed only to the attenuator sequence, and then transcription is terminated

Question 13

Describe operons involved in catabolism

Answer 13

(breakdown of a substance) are
usually off and typically inducible and the substance to be broken
down (or a related compound) acts as the inducer

Question 14

Describe operons involved in anabolism

Answer 14

biosynthesis of a substance) are
usually on and typically repressible and the inhibitor or corepressor is the small molecule that is the product of the operon

Question 15

Antisense RNA acts to?

Answer 15

control gene expression at the translational level to prevent translation from starting