Studying the Rate of Reaction of catechol oxidase and how it affects pH levels Introduction:
In this lab, we studied the activity of an enzyme that is found in fruits and vegetables called catecholase or catechol oxidase. An enzyme is a protein molecule that is a catalyst. Catechol oxidase is the enzyme in fruits and vegetables that turns them that undesirable brownish color; also commonly referred to as bruising or bruised. When walking through your regular grocery store and you find yourself in the produce section, what is it that you look for before putting that produce in the bag for weighing? The size, the smell, the color? Most of us would have to say that if they grabbed an apple that had a bruised body, they would return that apple to the pile in search for that perfect skinned apple. This is why studying catechol oxidase is so important! Let’s take a look at population numbers and why catechol oxidase is so important with the increasing number of people living on Earth. In 2010, the global population was estimated to be around 6.9 billion people (1). “From 2008 to the end of 2011, the number of hungry families in Washington grew from about 88,000 to 163,000… In 2011, 15.4 percent of Washington households reported some level of food insecurity, which means they regularly struggle to get enough food for their families, according to the USDA.” (2). With an increase like that in the amount of people struggling to feed themselves, how do we think it’s going to be when the expected population growth on Earth jumps to 9.6 billion in 2050 (1)? This is why studying catechol oxidase is so important. According to a UK news article back on September 19, 2013, “Up to two-fifths of a crop of fruit or vegetables can be wasted because it’s “ugly”… Produce grown in the UK that does not meet retailer standards on size or shape or is blemished is often used for animal feed or simply ploughed back into the ground even though it is edible, with as much as 40% of a crop rejected.” (3). Up to 40%! With people going hungry all over the world, if we were able to figure out how to reverse catechol oxidase or even halt it for a period, we would be able to have those fruits and vegetables out longer with purchasers willing to buy them because they still hold their “pretty” appearance. Before I get into more about the actual experiments done in the lab, let me explain in a little more detail about enzymes. Enzymes speed up chemical reactions and those chemical reactions then either consume or change the enzyme itself. Enzymes structures are three-dimensional that are built up by at least one or more peptide bonds that form what is known as an active site. The active site is where the substrate (catechol in this experiment) will go and attach. Many things such as changes in temperature and changes in pH can affect the structure of the active site which will affect the rate of reaction of how the enzyme contributes. Please see below for the chemical reaction done by catechol oxidase: (4)
This reaction is what causes the fruits and vegetables to brown or looked bruised. In the middle you see where the catechol oxidase (remember: it is the enzyme so that means it speeds up the reaction) comes into play. Catechol oxidases are found in the cytoplasm of the fruits and vegetables. When catechol oxidase is exposed to oxygen, it turns the fruits and vegetables brown. Remember how above I stated that many things can change the structure of the active site, such as pH? Well as it would have it, all enzymes are affected by changes in pH. Not only can it change the shape of the structure of the enzyme, but it can also change the shape or charges of the substrate as well. That can make it so the substrate is unable to bind to the active site making it unable to go through catalysis. So they work in what’s called the “lock and key” manner with the substrate. When the optimum pH level of an enzyme is met, it allows it to lock with the substrate to form...
References: Miller T., McFarland J., Landel H., Hansen C., Miller J. and Ma E. 2013. Biology 211 Majors Cellular Laboratory Manual [Lab Manual]. Biology Department. Edmonds Community College. Lynnwood, WA. 2015. PDF.
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