USA Biology Olympiad (USABO) Practice Exam

How can you confirm that a mixture of cellular organelles includes glyoxysomes and peroxisomes?

1. Visualize with electron microscopy

2. Perform an assay for the enzyme catalase

3. Examine for specific lipid compositions

4. Use fluorescence microscopy

The correct answer is: Perform an assay for the enzyme catalase

The most effective method for confirming the presence of glyoxysomes and peroxisomes in a mixture of cellular organelles is through performing an assay for the enzyme catalase. Catalase is a well-known enzyme that is primarily found in peroxisomes and is crucial for the breakdown of hydrogen peroxide into water and oxygen, a critical function carried out by these organelles. Glyoxysomes, which are specialized peroxisomes found in plants, also contain similar enzymes that can facilitate the conversion of fats to carbohydrates, but the presence of catalase specifically highlights the functional role of the organelles. While electron microscopy is a powerful technique for visualizing the ultrastructure of organelles, it may not provide the specificity needed to definitively distinguish between glyoxysomes and peroxisomes based solely on morphology. Likewise, examining lipid compositions might yield information about the types of membranes or potential functional characteristics but would not directly indicate the presence of these organelles. Fluorescence microscopy could be useful if specific fluorescent markers for peroxisomal proteins were available, but typically does not give the straightforward confirmation provided by enzyme assays. In summary, an assay for catalase directly targets one of the critical components and functions of peroxisomes and