Lab 13 Substitute – Yeast Catalase Activity “Yeast Sphere” is the name of my cover band.

The Background As you remember, the peroxisomes of a cell produce hydrogen peroxide (H2O2) as a byproduct of metabolism. Peroxide is a toxic substance to cells as it is a strong oxidizer and therefore must be broken down by the cells before it reaches high concentrations. This breakdown is the job of a very common enzyme called catalase.

The Test Subjects We’re going to monitor catalase activity with yeast cells. For consistency, standard yeast has been made into a 10% concentrated solution and has been encapsulated in a sphere of sodium alginate. Sodium alginate is a thickening agent in cooking. Importantly, these spheres sink in water.

The Procedure If we provide these yeast spheres with a substrate – peroxide, in this case – they will begin to metabolize it according to this reaction: 2H2O2 catalase 2H2O + O2 The peroxide solution is dilute (0.6%) to prevent immediate harm to the cells. When enough oxygen has been produced, the yeast sphere becomes buoyant and floats.

The Overview On Day 1, you’ll familiarize yourself with the procedure and collect your control group data. Simply drop your yeast sphere (one at a time) into 50 mL of peroxide in a 50 mL graduated cylinder. Start a timer either when the sphere strikes the surface of the peroxide OR when the sphere strikes the bottom of the cylinder.

The Overview Record the time it takes for 10 separate yeast spheres to sink and then rise. Following the second day of the lab, you’ll graph this data with a mean and 95% confidence interval (± 2 SEM). If you want/have time to do so, consider calculating your standard deviation and standard error now.

The Overview Last step for Day 1: Choose a variable. Consider what you know about the factors that affect enzyme activity and pick a variable you’d like to test. Then, develop a hypothesis (not a guess) as to how that will affect the enzyme and how this change would appear in lab data. Run this by me so I can be prepared, then revise your hypothesis (if necessary).

The Overview Day 2: Repeat the procedure but with your variable implemented. We’ll be influencing the yeast, not the peroxide (unless otherwise discussed). That means we’ll apply our treatment to the yeast whilst in the petri dish. All of the experiment can then be summarized in a formal lab report.

The Lab Report Stuff to research: Stuff to report: Other stuff: Yeast (Saccharomyces cerevisiae) ideal conditions, growing locations Relevant details for catalase Hydrogen peroxide pH (if applicable) Stuff to report: Mean, SD, SEM (with units) Sample size (n) for each data set Peroxide concentration (0.6%) HCl or NaOH concentration (3 M) and time spent soaking (if applicable) Time spent cooling (if applicable) Other stuff: You can’t identify anything as significant just by looking at the graph. Instead, you can say the results “suggest significance.”