Induction of Beta-Galactosidase

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Induction of β-Galactosidase

Syrita Saul

S12

Induction of β-Galactosidase

Hypothesis

I believe that β-Galactosidase will only be induced in the test tube containing the bacteria grown in lactose as β-Galactosidase is the enzyme that breaks down lactose.

Variables

My dependent variable, which is what I will be measuring, will be the presence of the enzyme β-galactosidase.

My Independent variable will be the addition of lactose to a culture of E-coli.

I will also have two control experiments to be able to compare the extremes. One with β-galactosidase originally present and the other with no bacteria present.

Planning

Genes are expressed in cells when the coded protein products are needed. This conserves the energy in the cell.

E-coli uses carbohydrates as a food source.

If lactose, found in milk, is in the E-coli growth medium it must be broken down into glucose and galactose before it can be used in respiration. This bacteria contains encoded in it a gene for the enzyme β-galactosidase which breaks down lactose. The presence of lactose activates this gene so the enzyme is then produce.

As the enzyme produced is colourless, it would be difficult to tell by eye alone whether or not the enzyme had been produced. To combat this, another colourless substance called ONPG is added to each reaction.

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ONPG is also broken down by β-galactosidase, it produces ONP a visible yellow liquid and galactose.

If yellow is seen, active β-galactosidase is present.

Equipment/Setup

Method

  • Wipe down all work surfaces with disinfectant.
  • Label four test tubes 1 to 4.
  • Add 5cm3 sodium phosphate solution to each test tube.
  • Using aseptic techniques (sterilising the test tube before each transfer using a Bunsen burner and a new sterilised pipette), transfer 1cm3 of the E coli bred without lactose into test tube 1.
  • Using the same technique, ...

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