Yeast and Lactose
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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Update: June 2012