Everyday Enzymes

As we continue with our Chemistry of Life unit, we are further building our knowledge of the importance of molecules as the building blocks of living things and today we learned about enzymes.  As we discussed, catalysts have important jobs in things as they are catalysts that speed up cellular reactions, even in our bodies like when we turn food into energy and oxygen into energy for muscles!  Enzymes work incredibly fast, and can speed up a reaction up to 10 million times faster!  What is really cool about enzymes is that they are made up of proteins and are proteins that are specific to a certain job, and are never used up!  So, once they speed up the reaction they are specific to do, they go back and do it again- they are reusable.

Lock and Key Model of Enzymes

To begin the lesson today, I showed the class a key that had a specific shape.  I then showed students various pictures of a lock and asked students if the key would work to open that specific lock.  Many students thought it was funny to even try to open a door using a key that had a different shape then the lock, and I agree!  Enzymes work just like a lock and key because a specific protein enzyme with only work with a specific substrate to speed up a certain reaction.  As with most lessons, this inquiry activity that also served as a good “hook” to get the attention of all students, worked well to make the information more visual for those that need to see the information being discussed, allowing more opportunities to connect with the new material.  We also learned that in order to be successful in the roles enzymes play, pH levels must be neutral (pH level of 7).  If the pH level is higher or lower than neutral, the enzyme will not work, similarly if the temperature is too hot or cold.  In addition, we discussed that most enzymes end in –ase, such as catalase.

One the new information was complete following the inquiry activity, a reading was completed in small collaborative groups discussing an enzyme that students encounter all the time!  The short reading is below:

Catecholase is an enzyme present in most fruits and vegetables, such as apples. It is what causes the browning of cut or bruised fruit or vegetables by catalyzing a reaction between the substrate molecule catechol and oxygen. The product of this reaction is polyphenol, which is a brown substance that gathers when fruits and vegetables are exposed to air. This color change is especially apparent in produce that has white flesh, such as apples and potatoes.

There are a few ways to prevent this enzymatic reaction. One is to submerge the fruit or vegetable in water. Water doesn’t affect the enzyme catecholase, but does reduce the availability of oxygen, part of the reactant required for the formation of polyphenol. This is why putting cut fresh potatoes in water delays browning.  Also, if the pH of fruit or vegetable is too high or low, than browning could be delayed as the enzyme does not have the conditions it needs to complete its reaction.

A few reading questions followed completion of this reading, as well as creating a hypothesis of a lab that would be completed at home.  Students were to make a hypothesis as whether a cut apple would brown faster or slower when rubbed with lemon juice, knowing that lemon juice is fairly acidic.

Now, it is the job of students to work with family members on this short experiment at home!  There has been much research completed, including that of Hill & Taylor (2004) that recognize that parent and family involvement in the educational process of students have higher levels of achievement, so this is a chance for both students and families to work together to come up with a scientific conclusion using the information provided.  Students may have to give a mini-lesson to parents of what they learned in class, but that is even better practice of the new content!  Parents/family, make sure to make a hypothesis on the students’ lab sheets!  The materials and procedures are below.

Materials:

·         1 Apple

·         1 lemon

Procedures:

1.    Slice the lemon in half

2.    Slice the apple in half

3.    Immediately rub the lemon wedge onto the open side of one half of the apple.

4.    Leave the other half of the apple flat on the table.

5.    Make observations for about 10 minutes of both slices of the apple onto a table such as the one below.

Observations
Apple Slice with Lemon Juice	Apple Slice without Lemon Juice

What might the different colors mean in terms of the enzyme, catecholase?

Now that you have completed the lab, describe your observations and explain why there were different results from each apple slice.  Make sure the use the content that we learned about enzymes!  What do your results tell you about how lemon juice may effects enzymes such as catecholase?  What happened the other apple slice?  Why did this happen?

Hill, N.E. & Taylor, L.C. (2004).  Parental School Involvement and Children's Academic Achievement.  Current Directions in Psychological Science, 13 (4).