Definitions:

Metabolism - the sum of all chemical reactions occurring in an organism.

Endergonic reaction- a chemical reaction that requires an input of energy.

Catalyst - a chemical that increases the rate (speeds up) chemical reactions.

Enzyme - a protein molecule that serves as a catalyst for biochemical reactions.

ATP - adenosine triphosphate.

Fundamental Concepts:

1) All organisms require a source of energy for maintenance and growth.

2) Heterotrophic organisms, including many microbes, use organic compounds as a source of energy.

3) Energy derived from organic compounds is temporarily stored in the high energy bonds of the ATP molecule.

4) ATP can be used immediately by the cell for all of its endergonic chemical reactions.

5) There are a wide variety of metabolic pathways organisms use to obtain energy (ATP).

6) Cellular respiration refers to three linked metabolic pathways used for the production of ATP from organic compounds, primarily carbohydrates.

7) Pathways of Cellular Respiration:

Glycolysis

Kreb’s Cycle (citric acid cycle, TCA cycle)

Electron Transport Chain

Glycolysis:

1) Anaerobic Pathway..

2) Common to many different types of organisms

3) Energy output relatively small compared to other pathways.

4) Splits glucose (6 carbons) into 2 pyruvic acid molecules (3 carbons).

5) Produces ATP and reduced coenzymes (NADH).

Kreb’s Cycle

1) Circular pathway involving the oxidation of pyruvic acid to carbon dioxide.

2) Initial step involves the conversion of pyruvic acid to acetyl CoA.

3) Produces reduced coenzymes (FADH₂, NADH) and ATP.

4) Carbon dioxide given off as byproduct.

5) Final product (oxaloacetic acid) combines with incoming acetyl CoA.

Electron Transport Chain

1) Aerobic.

2) Occurs on membranes.

3) Highest energy output of pathways.

4) Utilizes reduced coenzymes from other pathways.

5) A series of electron transfer reactions (oxidation-reduction).

6) Produces ATP from energy stored in electrons of reduced coenzymes.

7) Oxygen used as final reactant (electron acceptor).

© 1997, Department of Biological Sciences, Kent State University