Energy
Home Table of Contents Preliminary Information Introduction Energy Carbohydrates Proteins Nucleic Acids Wrap-Up

 

Photosynthesis
Respiration
Citric Acid Cycle
Electron Transport System
Fats for Energy
Proteins for Energy

Energy

Let's begin with the energy aspect of biochemistry.

There is a cyclic nature to the role of energy in life and the chemicals associated with it--particularly the chemicals. I've tried to illustrate that cyclic nature in this diagram. (This diagram is also shown in Example 2 of your workbook.) This is but one of many diagrams that could be used to try to illustrate this process.

Energy cycle diagram (ex. 4). [67004.jpg]

 

Photosynthesis and Respiration

To take you through this process quickly, notice that water and carbon dioxide can be combined together to make oxygen and glucose by a process known as photosynthesis. The oxygen is then made available in the atmosphere.

Then, through a sequence of steps, glucose can be worked into the citric acid cycle to generate carbon dioxide, water and energy. This overall process is referred to as respiration. This process depends on using oxygen made available by plants during photosynthesis.  The respiration process is used by both plants and animals alike.

 

Energy cycle diagram denoting respiration and photosynthesis portions. [67006.jpg]

 

Glucose and Related Chemicals

Quite a number of things can happen to glucose besides being used for energy. Glucose can be changed to cellulose, to starch, to glycogen, or to other chemicals, and then, of course, back to glucose also.

 

Energy cycle diagram showing related chemicals. [67007.jpg]

Plants use the glucose to make cellulose as a structural material. Any excess glucose can be converted into starch to be saved and used later when more glucose is needed, either for additional growth, additional chemicals, or additional energy.

Animals also can use glucose to make other chemicals. We can store excess glucose in the form of glycogen for short-term future energy use. Glycogen can be broken back down into glucose to run it through the respiration process to free up some energy to carry on the functions that are needed. Glucose can also be converted into fat as long-term storage for future energy use.

In this energy overview, the glucose can then be oxidized through a sequence of processes and be changed back to water and carbon dioxide. To oversimplify the process, plants can take water and carbon dioxide and photosynthesize them into oxygen and glucose. Plants and animals both can take the glucose, change it through a sequence of chemical reactions, oxidize the glucose back to water and carbon dioxide. Sunlight drives this process. The energy that is absorbed in this process is then made available to living things (plants or animals) to drive the various kinds of chemical reactions that are necessary in a living thing.

I think you can see that glucose has a fairly central role in the life process, in particular, the energy aspect of living things. In the other pages of this section we will look at the photosynthesis and respiration portions of this process in more detail.

 

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