unch was great: good food, good conversation. Now that the players were “full,” they were ready to play more volleyball. However, in order to play volleyball, their bodies first had to convert the food they ingested into “fuel” to burn, so they’d have the energy to contract their muscles to move their bones, and so their brains would have the energy needed to process incoming information, react, and send out orders. To harvest that energy, both their digestive systems and their mitochondria were involved, and a wide variety of enzymes had important roles to play.

Digestive System and Cellular Respiration

As food is ingested, where does it go on its way to becoming “fuel” for our bodies? First the food is chewed to break it into smaller pieces, and amylase enzymes in our saliva begin to break starches apart into sugars. Then the food is swallowed, and begins to make its way through the rest of the digestive tract.

These three sisters weren’t at this volleyball picnic, but they were at a similar picnic about 60 years ago, and they probably baked pies and made deviled eggs to bring along. Digestion of “protein foods” such as deviled eggs and hamburgers begins in our stomachs where the proteins are broken into shorter polypeptide chains. That was probably going on while these sisters were posing for this photograph!

The stomach absorbs some water and some nutrients, and the rest of the partially-digested food is passed on to the small intestine, where other enzymes further digest the food and more of the nutrients are absorbed. Then the large intestine absorbs water and some more nutrients and eliminates the “left-overs.”

All of those absorbed nutrients float along in the blood, traveling to other places in the body. Many, like vitamin A and sugar, are stored in the liver. A portion of the circulating sugar is also absorbed by brain and muscle cells where the cells’ mitochondria burn the sugar (and some fats and amino acids) as fuel via a process called cellular respiration.

However, when our bodies burn sugar for fuel, we can’t do it all in one step, or we’d end up with a bonfire, like this, in our bodies! That might be OK for fictitious, fire-breathing dragons, but for the rest of us, still more enzymes break the sugar apart in many, smaller steps and release the energy gradually. That way, the heat that is released is just enough to keep us warm, but not enough to start us on fire.

Our cells can, then, use that energy for other purposes. Muscle cells can use energy to contract and brain cells use energy to process and send the electrical impulses that keep us going. Thus, if everything is working together as it should be, then a person can play volleyball, study biology, play a musical instrument, smile at someone else, etc.

Enzymes are proteins that function as biological catalysts: they help chemical reactions to take place, but they are not part of the reaction. For example, the enzyme, maltase is the right shape to match up with a molecule of maltose sugar. Then the maltase causes the maltose to break into two molecules of glucose, which are then released, and the maltase is ready to accept another maltose and begin the whole process, again.

The first enzymes to be discovered and studied are those which are found in yeast, which the yeast use to ferment sugar and turn it into alcohol and carbon dioxide. Humans have made use of yeast and their enzymes for centuries to produce bread, beer, wine, and mead. The process of fermentation is another means of harvesting energy from food and shares its first big step, called glycolysis, with the process of cellular respiration that our cells use.

Background Information

Links to Related Information on Our Web Server

The following Web pages contain information related to digestion of various nutrients in our food and how our cells harvest energy from our food.

Bio Lecture Carbohydrates

Pay special attentionto the sections near the bottom that discuss sugar utilization by our bodies.

Bio Lecture Cellular Respiration

This is the process by which our cells burn previously-ingested, digested, and absorbed sugar for fuel.

Bio Lecture Digestive System

Information on how our bodies digest and absorb food

Bio Lab Enzymes Activity

An activity to show the effects of pH and temperature on several enzymes’ ability to function

Bio Lab Pepsin Activity

An activity to show the effect of antacids on pepsin’s ability to digest the protein in one’s diet

Your Assignment
An Example of Fermentation

Most of us, fairly regularly, ingest foods that yeast enzymes helped make, such as bread, root beer and ginger ale, or beer and wine. Some people also like yogurt, made by a “good” bacterium called Lactobacillus acidophilus via a fermentation process which produces lactic acid rather than alcohol and carbon dioxide. If you’ve never tried making any of these before, here’s your chance. The grading criteria for this assignment are given below, and you should also refer to those as you work on the assignment. A total of 16 points is possible.

1. Pick one of the following recipes to try. The root beer is good, but it can be hard to find the extract you’ll need for that. The “lab brew” takes some special supplies and equipment and a longer time to do, but I’ve included it here in case anyone is interested. Bread is fairly easy, but does take a couple hours (and smells delicious when it comes out of the oven!). If you have another bread recipe you’d like to try rather than this one, that’s OK, as long as it’s yeast-raised bread (not a “quick” bread). Yogurt is easy to make. If you have another fermented recipe of your own you’d like to try, that’s a possibility, but e-mail your instructor to obtain permission, first.

   Dr. Fankhauser’s Homemade Root Beer

   The original recipe for and more information on the root beer we make in lab

   Dr. Fankhauser’s Homemade Ginger Ale

   Many herb books mention that ginger is good for soothing an upset stomach

   Dr. Fankhauser’s Recipe for Whole Wheat Bread

   Yummy, nutritious, whole-grain bread

   Dr. Fankhauser’s Homemade Yogurt

   An easy recipe

   Bio Lab Brew Activity

   A recipe to study the process of fermentation

2. Make the recipe you have chosen. Take notes on what you did. How did it turn out? How did it taste when it was done? How did what you observed as you made your recipe relate to what you have learned from the reading you have done on this topic?
3. At this point, if you are a registered student, you should submit your notes.

Grading Criteria

1.   Observations and Notes on Recipe Tried:
2	—	The student was very observant as (s)he made his/her recipe and took excellent notes
1	—	The student observed and took adequate notes
0	—	The student’s notes are sketchy and suggest that (s)he did not pay much attention to what was happening
2	—	The student clearly observed, understood and explained the role of fermentation in this recipe, including what was doing the fermenting and what was being fermented
1	—	The student at least acknowledged and showed a minimal understanding of the role played in this recipe by the process of fermentation
0	—	Little, if any, thought was given to the role of the process of fermentation in this recipe
2	—	The student clearly recognized why bread rises and smells good, what gives root beer its fizz, or what causes yogurt to set up
1	—	The student at least acknowledged the role of fermentation in the one of these that pertains to his/her recipe
0	—	The student demonstrated little, if any, recognition of why his/her recipe worked the way it did
2.   Demonstration of Background Knowledge:
2	—	Overall, the student demonstrated a thorough knowledge and understanding of the process of fermentation as a means whereby cells harvest energy
1	—	Overall, the student demonstrated at least partial knowledge and understanding of the process of fermentation
0	—	Overall, the student demonstrate little, if any, knowledge and/or understanding of the process of fermentation
2	—	The student demonstrated a thorough knowledge of how yeast or bacteria cells use enzymes to digest their food
1	—	The student demonstrated at least some knowledge of how yeast or bacteria cells use enzymes
0	—	The student demonstrated little, if any, knowledge of how yeast or bacteria cells use enzymes
2	—	The student clearly and thoroughly made the connection between yeast/bacterial use of enzymes and our use of enzymes to digest our food
1	—	The student demonstrated at least some knowledge of the similarities in digestive enzyme usage between these various organisms
0	—	The student demonstrated little, if any, knowledge of these similarities
3.   Overall:
2	—	The student, obviously, went beyond the minimum requirements of the assignment
1	—	The student adequately completed the assignment
0	—	The student completed considerably less of the assignment than what was required
2	—	It is evident that the student used much insight, thoughtfulness, and critical thinking when completing this assignment
1	—	The student adequately thought about the assignment – there was, perhaps, a bit of “fuzzy thinking” in a couple places
0	—	The assignment gives the appearance of being “slapped together” just to get it done, with little evidence of thoughtfulness
Total Possible:
16	—	total points