lactose question

Please can anyone help me with this question, thanks:

The bacterium E. coli uses glucose as a respiratory substrate. In the absence of glucose, E. coli can use lactose.

Explain how lactose induces the enzyme system involved in its uptake and metabolism.

Reply 1

Michael Scofield

Erm not sure about what the question is asking but from memory, lactose 'switches on' the genes that code for the synthesis of beta-galactosidase and lactose permease. Beta-galactosidase is then used to hydrolyse lactose to glucose and galactose. Lactose permease enables the cell to then take up lactose. Basically, in the presence of lactose, the genes are said to be 'expressed', and hence they can produce those two enzymes. Hope that helped and I'm sure I didn't answer the question. But hey..

Reply 2

Tom H

The lactose genes' transcription is controlled by an area called the lac operator. A protein called the lac repressor binds this operator preventing RNA Polymerase from moving down the DNA and transcribing the lactose genes.

When lactose is present in the cell it binds the lactose repressor, inducing a conformational change and causing it to fall off the DNA, allowing RNA Polymerase to transcribe the genes.

Hope that helps.