STEP-BY-STEP GLYCOLYSIS
Organisms stay alive by taking in food. This food is then broken down in catabolic pathways to provide cells with energy to carry out cellular activities. The energy currency in living systems is adenosine triphosphate (ATP). Therefore, the objective of catabolic processes is to produce ATP. The breakdown of glucose by means of glycolysis is the first step of the major energy-releasing pathways. This reaction sequence takes place in the cytoplasm of both prokaryotic and eukaryotic cells.
Glucose is a six-carbon sugar. In the process of glycolysis, glucose is converted into two three-carbon molecules of pyruvate. This breakdown is accomplished through a series of events including phosphorylation, dehydration, oxidation, and reduction. In the absence of oxygen, pyruvate can be further converted to lactate. The conversion of pyruvate to lactate often takes place in the muscles during vigorous exercise as oxygen in the tissues becomes depleted.
ACTIVITY
While it is possible to simply memorize the reactions in glycolysis, in order to understand the process, it is important to know why each step takes place as it does. The site you will use includes biochemistry materials created by Jon Maber. In the activity you will choose the individual reactions in the conversion of glucose to lactate. If you choose an incorrect, illogical, or impossible reaction, the site will provide you with hints for the correct selection. If you choose the correct reaction, you will be directed to the next step.
It is very important that you have a basic understanding of the steps in glycolysis before you begin this activity. In addition, it is important to understand the processes of phosphorylation, oxidation, reduction, and the generation of ATP.
Use your browser to go to http://www.jonmaber.demon.co.uk/.
Choose "Design It Yourself Glycolysis" from the menu under "Glycolysis."
Read the material in the introduction and the links that follow it (ending with a summary of reaction types).
When you are ready to begin the actual exercise, click "Begin with Glucose." The page will prompt you to answer the question, "Why are you using this site?" Select "I'm required to work on it as part of a course." Continue to the exercise itself.
In each subsequent step, select a reaction type from the list. If you choose incorrectly, read the complete explanation on the screen before using the back key of your Web browser to return to the previous page. The explanations of incorrect selections will help you choose the correct reaction. If you choose the correct reaction, scroll back to the top of the page and choose the next step. Throughout each step the number of ATPs produced or spent will be tallied at the bottom of each page.
Continue working through the selections until you have successfully converted glucose to lactate.
You may find it helpful to use Figures 7.4 and 7.9 in your text for reference as you work.
As you work through the exercise, answer the following questions: