For High School Teachers
 
  From DNA to Organism: A Study in DNA Function for the High School Biology Classroom
 
 

Module 4: Yeast and the gene

Quantitative analysis

     Tips for culturing yeast cells

  1. You need a small sample of yeast to begin a culture. Typically you will start with about _______ (depends on teacher preference; the teacher can set up the stock yeast culture to have varying concentrations to allow for students to pipette a convenient volume) yeast

  2. Use the small test tubes, called cuvettes, to grow your yeast cells in. The advantage of using these is that we can evaluate growth using the spectrophotometer (see the How the Spectrophotometer Works handout—It is a ppt slide that is not attached to this file yet).

  3. Add ______ (depends on teacher preference; the teacher can set up the stock yeast culture to have varying concentrations to allow for students to pipette a convenient volume) ml of media to each of the tubes using the pipettes. If you are using different media types, make sure to label which tube gets which.

  4. Add ______ (depends on teacher preference; the teacher can set up the stock yeast culture to have varying concentrations to allow for students to pipette a convenient volume) ml of your yeast sample to the cuvette. Make sure to mix the yeast culture up before you sample from it, yeast tends to settle at the bottom.

  5. After you have added your sample to the growth media, mix the sample up and use the spectrophotometer to measure the absorbance of it.  

    1. The absorbance on a spectrophotometer measures how much light can pass through the sample, or how much light the sample absorbs. The more yeast cells that there are in the sample, the more light that they will block, and the higher the absorbance of the sample. In other words:

Lower absorbance = fewer cells in the culture
Higher absorbance = more cells in the culture

              Record your absorbances in your notebook.

  1. Place your prepared cultures into a rack and leave them in the incubator for 24– 48 hours to grow.

     Assessing your cultures after they have grown

  1. After 24– 48 hours of growth, remove your tube from the incubator.
  2. Carefully shake each tube and place it into the spectrophotometer to test the absorbance. Make sure to wipe the side of the tube before you put it into the spectrophotometer.
  3. Record your absorbances in your notebook.