Introduction to Aerobic Respiration

If you think eating is something you do for pleasure, think again. One of the main reasons for eating is to provide your body with carbon sources (carbohydrates, fats and proteins) that can be used for energy (i.e. to make ATP).

We are going to do a very brief overview (believe it or not) of some very complex chemical pathways. You are not responsible for knowing the chemical structures of any of the compounds or the step by step details of the reactions. Let the review questions be your guide to the depth of understanding required.

The nucleotide ATP (adenosine triphosphate) is the prime energy carrier for all cells, both autotrophic and heterotrophic.

All energy-releasing pathways whether aerobic (requiring oxygen) or anaerobic (not requiring oxygen) begin with a pathway called glycolysis, which occurs in the cytoplasm (cytosol).

Fermentation (anaerobic) pathways and anaerobic electron transport can release small quantities of energy without the use of oxygen. Fermentation produces a net yield of two ATP.

Aerobic respiration is the main energy-releasing pathway leading to ATP formation. It occurs in the mitochondria. Aerobic respiration yields thirty-six ATP.

AEROBIC RESPIRATION

In plain English, one molecule of glucose plus six molecules of oxygen are broken down into six molecules of carbon dioxide and six molecules of water.

In a future lecture you will see that the equation for aerobic respiration is essentially the reverse of the equation for photosynthesis, which is how plants make food:

Aerobic Respiration consists of the following three pathways:

• Glycolysis
• the Krebs Cycle (also known as the Tricarboxylic Acid Cycle or TCA Cycle), and
• Electron Transport Phosphorylation (also known as the electron transport system or ETS).

The end products of the Krebs Cycle in turn feed into the electron transport system, also located in the mitochondria.

Three series of reactions are required for aerobic respiration:

1. Glycolysis is the breakdown of glucose to pyruvate. Small amounts of ATP are generated.
2. The Krebs Cycle degrades pyruvate to carbon dioxide, and water. ATP is produced. NAD and FAD accept H+ ions and electrons to be carried to the ETS.
3. Electron transport phosphorylation processes the H+ ions and electrons to generate high yields of ATP. Oxygen is the final electron acceptor.