Class: BE210
Group: T2
Members:

Date: April 2004

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Abstract: 

Studying the growth of Saccharomyces cerevisiae (Baker’s yeast) can give insight into cell growth, replication, and death.  Yeast experiments are important for the understanding of reaction equilibrium and rates.  Thus, yeast growth studies have applications to cell culture and biotechnology.  Yeast provides a good model to compare to mammalian cells because several cellular functions are similar to those in yeast, and corresponding genes between yeast and mammals complement each other.  In addition, since yeast is a unicellular organism, it can be grown rapidly.  In yeast growth, the components in the medium play an important role in the rate of growth.  Glucose is one of the necessary components because yeast breaks down sugar to produce energy necessary for metabolic processes.  Sugar is digested by the yeast through glycolysis and the Krebs cycle.  Therefore, measurement of the glucose consumption is directly related to yeast metabolism and growth.  

This experiment will also focus on the effect of buffering the growth media.  The pH of the medium greatly affects the consumption of glucose in two ways.  First, due to the acidophilic nature of yeast, the cells will grow better in an acidic environment with an optimal pH between 4 and 6.  In this optimal range, the enzymatic processes within the yeast will function properly and the growth rate will be at a maximum.  As mentioned above, glucose consumption is necessary in order to satisfy the energy requirements needed for these enzymatic processes to work.  However, glucose consumption is also affected due to the cellular mechanism used to bring the glucose into the yeast.  This mechanism involves the use of a hydrogen pump to take in glucose molecules that are too large to cross the cell membrane by passive diffusion.  A hydrogen pump is formed when a cell uses energy from ATP (adenosine triphosphate) to actively pump hydrogen ions out of the cell and against its concentration gradient.  After the hydrogen ions are pumped out, they travel back down their concentration gradient and into the cell, carrying glucose molecules along with them.  Moreover, an extracellular medium with a higher alkalinity will allow this pump to perform at optimal efficiency due to the pH gradient, i.e. the hydrogen ions will be easier to pump into a basic medium.  Therefore, the optimal pH for the hydrogen pump will be around 7, while the optimal pH for yeast growth is between 4 and 6.