Question

1) Describe the similarities and differences between the lac operon in E. coli and the GAL system in yeast.

2) What effect does mutation at nucleotides within a silencer element have on the expression of the gene associated with the silencer? Why does it have this effect?

Answer 1

1)

Similarities between lac operon in E. coli and the GAL system in yeast:

Lac operon	GAL system
1. Inducible system of gene expression	1. Inducible system of gene expression
2. In presence of the inducer (allolactose) the system remains on condition.	2. In presence of inducer (D-galactose) the system remains on condition.

Difference between the lac operon in E. coli and the GAL system in yeast:

Lac operon	GAL system
1. Gene regulatory system present in prokaryotic cells.	1. Gene regulatory system present in eukaryotic cells.
2. Here the inducer is allolactose.	2. Here the inducer is D-galactose.
3. Gene components are different from GAL system.	3. Gene components are different from lac operon.

2)

Silencers are genetic component which bind with the repressor protein and inhibit the transcript of a gene. If the mutation at nucleotides in the silencer element change its potentiality to bind with the repressor protein then continuous transcription of the downstream genes are occurred.