Question

Compare and contrast the structure and function of the lac operon with the arabinose operon.

Answer 1

1) Arabinose operon is required to metabolism of L-arabinose in E.coli and Lac operon is required to transport and metabolism of lactose in E.coli.

2) Arabinose and lac operone contain three structural gene each.

3)Three structurual gene in arabinose operon is araB(ribulokinase), araA(isomerase) and araD(an epimerase).In lac operone lacZ (beta-Galactosidase), lacY (Beta-galactoside permease) and lacA (Beta galactoside transacetylase).

4)Both arabinose and Lac operon contain regulatory gene araC and lacI which encode the repressor protein.In presence of arabinose and lactose which activates the transcription and translation of metabolic enzymes respectively and in the absence of arabinose and lactose which inhibits the transcription and translation of metabolic enzymes of both operon.

Function of arabinose Operon: araA encode L-arabinose isomerase- isomerized the L-arabinose and L-ribulose. araB encode ribulokinase which phosphorylate to L-ribulose to form L-ribulose-5-phosphate.araD encode L-ribulose-5-phosphate epimerase which form D-xylulose-5-phosphate intermediate of pentase phosphate pathway.

Function of Lac operon: lacZ encode beta-galactosidase which break lactose into glucose and galactose.

lacY encode beta-galactoside permease which transport beta-galactoside(lactose) into the bacterial cells by using proton gradient.

lacA encode Beta galactoside transacetylase which trasfer acetyl group from acetyl CoA to beta-galactoside.