Chapter 1.3 - The Iac Operon Flashcards
What two enzymes are produced is the bacterium E.coli is grown in a medium where there is lactose present?
B-galactosidase and lactose permease.
What does e.coli respire?
Glucose usually but also when lactose present lactose
What is the role of b-galactosidase and lactose permease?
B-galactosidase breaks down lactose into glucose an galactose.
Lactose permease transports lactose into the bacterial cell.
When are the enzymes produced?
The enzymes are only produced when lactose is present so therefore lactose is the inducer for B-galactosidase and lactose permease.
What is an operon
An operon is a length of DNA which is made up of structural genes and control sites. The structural genes code for the enzymes and the control sites consist of an operator region and a promoter region. These regions regulate the operon
What are the 2 structural genes on the lac operon
The z-site and the y- site.
The z-site codes for the enzyme B-galactosidase and the Y-site codes for the enzyme lactose permease.
What is the operator region
The operator region is a length of DNA alongside te structural genes z and y and can switch them on and off.
What is the promoter region
The promoter region is another length of DNA which the enzyme RNA polymerase binds to in order to begin transcribing the mRNA for synthesising the enzymes from z and y when appropriate.
What is the role of the regulator gene
Whether there is or isn’t any lactose present, the regulator gene is expressed (transcribed and translated into a protein) so that the repressive protein in synthesised.
What is a repressive protein
A repressive protein binds to the operator region and has a second binding side for lactose to change it’s shape. When it binds to the operator region it prevents RNA polymerase from biding to the promotors region and transcribing the z and y site Into the two enzymes.
What happens in the lac operon when lactose is absent from the medium growth.
1) he regular gene is expressed and the repressor protein produced.
2) no lactose is present to bind to the repressor protein so the protein binds to the operator region of the operon, also part of the promotor region (where RNA polymerase attaches to begin transcription)
3) as the repressor protein has bound itself to the operon, RNA polymerase cannot bid to the promotor region to transcribe the z and y sites into mRNA to be expressed.
4) without the mRNA being produced, the 2 enzymes are not synthesised.
Why are the advantages if the lac operon not producing the enzymes when no lactose is present in the medium?
Useful resources are not wasted by making unnecessary enzymes.
No point wasting emery and resources making enzymes if they are not needed.
What happens in the lac operon when lactose is present in the growth medium?
1) the regular gene is expressed as normal, so the repressor protein is still produced.
2) the inducer molecule (lactose) binds to the repressor protein causing the shape of the repressor protein to alter so that the binding site wi not be complementary to the operon.
3) the repressor protein does not therefore bind to the operon or it breaks away if it is already present on the operon.
4) the RNA polymerase is able to bind to the promotor region and transcribe Z and Y into B-galactosidase and lactose permease, so lactose can be brought into the cell, broken down and respites.
