KEGS Biology Blog


YEAR 13 Tuesday 4th December
December 4, 2012, 11:28 am
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Lac operon

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The Lac Operon (genes can be switched on and off)
E. coli
Operon – a selection of DNA that contains 3 types of genes:
Structural gene-Produces useful proteins e.g. Hb, enzymes, collagen
Control gene-Promoter region which is where RNA polymerase binds together before the structural gene so it can be transcribe structural gene
Regulator gene- Switches that can control transcription. Transcription factors (activator and repressors) – proteins

Lac operon found in E. coli
Lac operon is only expressed in presence of lactose when glucose been used up
E. coli reproduces every 20 minutes – high reproduction rate
Common
Not many genes
Genetic DNA is held within a plasmid – use restriction enzymes to cut out small part of gene and implant others

Lac operon can respire glucose and if no glucose present it can respire lactose.
Component Function
Structural genes Codes for lac enzymes
Regulator gene Produces repressor protein
Promoter Binds to RNA polymerase
Operator Binds to the repressor

The function of the repressor protein is that it can bind to the operator region and RNA polymerase binds to the promoter region to transcribe the structural genes
Lactose is an inducer because it induces transcription of the 3 structural genes. It also binds to repressor molecule and changes its shape then leaves the operator region
An advantage to E Coli bacteria of having lac operon system to induce enzyme formation because it does not waste any resources as it is only expressed in the presence of lactose when all glucose has been used up.

KEY DEFINITIONS
An operon is a length of DNA, made up of structural genes and control sites. The structural genes code for proteins, such as enzymes. The control sites are the operator region and a promoter region.

The operator and promoter are both genes as they are lengths of DNA. However, they do not code for polypeptides.

A repressor protein can bind to the operator region, and RNA polymerase binds to the promoter region to transcribe the structural genes.

( source= class notes and OCR biology A2 text book )

Comment by frankiebarrick




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