Lac Operon Flashcards
In prokaryotic cells what are the groups genes are put in
Operons
What is an operon
A group of genes under the same regulatory mechanism and are all transcribed in one single unit
Why are operons useful
Genes that code for proteins involved in a specific metabolic pathway can all be switched on or off
What do bacteria use as their main respiratory substrate and why
Glucose as it is very easy to metabolise
What can bacteria also use as a respiratory substrate
Lactose
What has to be done so that lactose can be metabolised
Different proteins must be produced
When are proteins required to metabolise lactose produced
When glucose is absent
Where are the genes that code for proteins needed for lactose metabolism located
In an operon (the lac operon)
What does it mean that all the genes that code for proteins needed for lactose metabolism are in an operon
They can be easily repressed when they are not required
Describe the structure of the lac operon
It is a section of DNA that has an operator region, a promoter region and 3 structural genes: lacZ, lacY and lacA (THEY CODE FOR PROTEINS)
Describe the structure of the section of DNA located near the lac operon
Contains the regulatory gene lac I
What does the gene lacZ code for
The enzyme B-galactosidase
What does the enzyme B-galactosidase do
Catalyses the hydrolysis of the disaccharide lactose into glucose and galactose
What does the gene lacY code for
The membrane carrier protein lactose permeate which helps transport lactose into the bacterial cell
What is the promoter region
The section of DNA where the RNA polymerase binds in order to begin transcription
What is lac I
The regulatory gene
What does the regulatory gene lac I do
Codes for a protein that prevents transcription for the structural genes - repressor protein
What is the operator region
The section of DNA that the repressor protein binds to in order to prevent transcription
What occurs in the absence of lactose
Transcription of the lac genes is always repressed (genes are switched off)
Why is the transcription of the lac genes repressed in absence of lactose
Regulatory gene lac I is always switched on, resulting in production of repressor protein which binds to the operator region which is next to promoter region. This prevents RNA polymerase from being able to bind and therefore prevents transcription
What does the presence of lactose allow
The transcription of the structural genes
What is produced as a result of transcription of the structural genes
B-galactosidase and lactose permease
How does lactose allow the transcription of the structural genes
It acts as an inducer by binding to the repressor protein and causing it to change shape and prevents it from being able to bind to the operator region
What occurs as a result of repressor protein no longer binding to operator region
RNA polymerase is able to bind to the promoter and transcription of the structural lac genes can occur
What is the purpose of the lac operon
Conserves resources by only metabolising lactose when required
