Prokaryotic Lac operon

Question 1

What is the significance of the lac operon in bacteria?

Answer 1

This cluster of genes codes for the production of lactose enzymes that allow the bacteria to obtain glucose from lactose when readily available glucose is not present in the environment.

Question 2

What is the purpose of the lac z gene?

Answer 2

The gene encodes for beta galactosidase that breaks lactose down into glucose and galactose.

Question 3

what the the purpose of the lac y gene?

Answer 3

Encodes for permease that transports lactose into the cell.what

Question 4

What is the purpose of the lac a gene

Answer 4

Encodes the transacetylase enzyme that removed toxic thiogalactosides.

Question 5

True of false. All genes are in the lac operon are downstream of the Ame promoter

Answer 5

True.

Question 6

What’s the process behind switching the operon off.

Answer 6

1. LacI repressor sequence transcribed then translated into active repressor protein.
2. ARP binds the operator region.
3. transcription of the rest of the gene does not occur.

Question 7

What the process behind switching the operon on?

Answer 7

1. Active repressor protein expressed.
2. Allolactose binds repressor protein to inactivate it.
3. Transcription the rest of the operon is permitted.

Question 8

What condition constitute the operon being off.

Answer 8

1. Glucose present, Lactose absent (no CAP)
2. Glucose present, Lactose present (no CAP)
3. Glucose absent, Lactose absent (CAP bound because there is not glucose).

Question 9

What is the consequence of mutations in the promoter?

Answer 9

RNA polymerase would not be able to bind so there is the possibility that no transcription of any of the operon’s gene would occur.

Question 10

What is the consequence of nonsense mutations in the lac z gene?

Answer 10

This could interfere with the expression of the other two genes downstream because the ribosome would dissociate prior to their translation.

Question 11

What are the 4 patterns of splicing?

Answer 11

1. optional exon
2. optional intron
3. mutually exclusive exons
4. internal splice sites

Question 12

What is intron ambiguity and how does it lead to alternative splicing?

Answer 12

this is the inability to distinguish between splice sites which leads to the inclusion or exclusion or introns or exons in different mRNA molecules.

Question 13

What is negative regulation of splicing?

Answer 13

A repressor blocks splicing which exposes weak splice sites and prevents use of strong splice sites so splicesosomes use inefficient or weak splice sites.

Question 14

What is positive regulation of splicing?

Answer 14

An activator directs the splicesosome to recognize overlooked sites and suppress competing sites.

Question 15

Normal splicing

Answer 15

wild type protein

Question 16

Exon skipping

Answer 16

in frame deletion - deletion of a multiple of 3.

Question 17

alternative 5’ splicing

Answer 17

cutting off part of the exon towards the 5’ side resulting in an alternative amino acid sequence in the protein.

Question 18

Alternative 3’ splicing

Answer 18

partially cutting off the exon towards the 3’ end resulting in an out of frame/frameshift deletion

Question 19

intron retention

Answer 19

insertion of amino acids in the sequence.

Question 20

mutually exclusive exons

Answer 20

results in segments of mRNA not in the same molecule causing different amino acid sequences entirely. This could be a function of steric interference of splice sites close to each other resulting in splicesosome incompatibility.