Class: BE210
Group: W9
Members:
Noura Selim
Andrea Levine
Shirley Duarte
Edward
Yang
Ranliang Hu
Date: April 2004
Abstract:
The growth of Saccharomyces cerevisiae, commonly referred to as
Baker’s Yeast, depends on both the presence of as well as the type of
nutrients. In the lag phase of growth, the yeast adjusts to their new
environment by synthesizing new enzymes and proteins. Nutrients are
consumed during the lag phase. Depending on the type of nutrients
present, the length of this phase will vary. If the yeast is grown long
enough, it will experience a few lag phases depending on the number of
different nutrients present. In the log phase, the yeast also consumes
nutrients, which are present in excess, as they are needed for
replication. However, as the cycle continues, nutrient depletion
occurs.
S. cervisiae is dependent on glucose as a primary form of energy. In
order to provide the yeast with nutrients, the typical yeast diet
consists of dextrose, peptone, and yeast extract. These different diet
components represent different forms of nutrients. Dextrose is a form
of glucose. Peptone is derived from proteins, and yeast extract is
produced from autolysed yeast cells. In order to measure the yeast’s
glucose consumption, a glucose (HK) assay kit will be used. This kit
measures glucose consumption through the change in absorbance that
occurs due to the phosphorylation of glucose and the reduction of NADH.
Specifically, first glucose is phosphorylated using ATP. The inorganic
phosphate binds to the glucose, making it glucose-6-phosphate. This
reaction is catalyzed by hexokinase. In the final reaction,
glucose-6-phosphate is reacted with NAD to form 6-phosphogluconate and
NADH. This reaction is catalyzed by glucose-6-phosphate dehydrogenase.
The reduction of NAD to NADH causes an increase in absorbance at 340
nanometers, which is proportional to the change in glucose
concentration. The change in glucose concentration over time would
equal the yeast’s consumption of glucose.