|[Previous] | [Next]|
Basic Energy Concepts
Types of Catabolism
Catabolism of Fats
Catabolism of Proteins
Summary of Catabolism
Basic Energy Concepts
©2000 Timothy Paustian, University of Wisconsin-Madison
Before we dive into bacterial metabolism I want to present some over arching ideas that you should keep in mind as we explore how bacteria make their energy and what they use it for.
First let me impress on you an important idea. Thousands of years ago, human tribes worshiped the sun. The light and heat of the sun was pivotal to their survival. Life on earth is possible because of the energy generated by the sun and almost all life depends upon it. (OK, OK, organisms living at deep sea ocean vents don't need the sun.)
This ultimate source of energy is transformed into living matter. To start getting comfortable with this idea, let's look at thermodynamics, which is concerned with the storage, transformation and dissipation of energy. Cells store energy, they transform it and they dissipate it to drive unfavorable reactions. Here we introduce the laws of thermodynamics because they govern everything a cell does.
The first law of thermodynamicsEnergy can neither be created nor destroyed in the universe.
For living organisms this means they must collect and convert existing energy into a form suitable for biological processes from the surrounding environment. Usually this means grabbing it from the sun or breaking down large molecules and releasing the energy in them.
The second law of thermodynamicsIn all processes or reactions, some of the energy involved irreversibly loses its ability to do work.
orIn any reaction the amount of molecular disorder always increases
Living systems are ordered, while the natural tendency of the universe is to move toward systems of disorder with unavailable energy (increasing entropy). A cell is a protest against the second law of thermodynamics! Organisms are in a constant battle with entropy and when they finally lose the war, they die. Ah the futility of existence....
Free Energy (delta G)
All chemical reactions can be describe by the following equation.
This equation can be rearranged as follows
Think about this for a moment. Increasing DS (entropy) results in a disordering of the system, giving a negative DG. So things that result in a large amount of disorder, like breaking starch (a polymer of sugar) into carbon dioxide and water, are favorable and result in a negative DG value. The take home message - negative DG (free energy) is good and is available to do work in the cell.
|This page was last built with Frontier and Web Warrior on a Macintosh on Thu, Sep 21, 2000 at 1:16:22 PM.|