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Name: Kate
Status: Other
Grade:  Other
Location: CA
Country: United States
Date: April 2005

Our class performed an experiment where yeast was placed into 2 tubes, one containing glucose and the other containing lactose. Growth occured in the tube with glucose and a gas bubble formed indicating the yeast was able to perform fermentation. No growth however occured in the tube with lactose and i dont understand why? is it because the yeast was unable to break the lactose down into glucose?

Yes. There is an enzyme, beta-galactosidase or lactase, that breaks lactose down into glucose + galactose. If the yeast don't produce this enzyme, they are unable to use lactose as a carbon and energy source.

Ron Baker, Ph.D.

You are absolutely correct! Remember that all biochemical reactions require enzymes to make reactions occur at useful rates. There is an enzyme that catalyzes the breakdown of lactose into glucose. Enzymes are proteins and therefore are coded for by genes and the yeast you used doesn't have this gene. I will let you look up the name of this enzyme.


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