Dr. Ray L. Winstead
Professor of Biology, Indiana University of Pennsylvania

Cellular Metabolism
and Metabolic Pathways

A. Types of metabolism

    1. Catabolism - all the chemical reactions that break down larger molecules into smaller molecules.
    2. Anabolism - all the reactions that combine smaller molecules into larger molecules.

B. Metabolic Pathways - Generalizations

1. All metabolic pathways consist of a number of discrete steps - a series of chemical reactions.

2. Each step is a highly specific chemical reaction, so that the end of the chain of reactions is highly specific.

3. Particular pathways are located within certain regions of a cell, e.g., in a particular organelle.

4. Every pathway as a whole and every discrete step of a pathway involves energy exchange.  The study of energy transformations in living organisms is bioenergetics.  Bioenergetics is a branch of thermodynamics, which deals with all forms of energy and its transformations.

5. Every discrete step in a metabolic pathway is catalyzed by a specific enzyme.  The enzyme is functioning as a catalyst, a chemical that controls the rate of a chemical reaction.

6. Chemical reaction rates adjust to the cell's current requirements.

7. All metabolic pathways are interrelated. 

C. Energy Transformations

    Three major types of biological energy transformations:

    1. Energy from the sun is used in the process of photosynthesis in plants to produce a chemical form of stored energy, i. e. glucose sugar.

    2. Stored energy in glucose is transformed through the process of cellular respiration into a more usable form of stored energy in energy-rich phosphate bonds in ATP = adenosine triphosphate.  This type of energy transformation occurs primarily in the mitochondria within cells.

    3. The chemical energy in phosphate bonds in ATP is released and directly drives other chemical reactions in cells.

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Dr. Ray L. Winstead
Direct e-mail Link: RWinstea@iup.edu