1. Cellular Respiration Biology 11
Biology 11 Advanced

2. The Beginning Three major stages of cellular respiration:
1. Glycolysis (splitting of sugar)
2. The Citric Acid Cycle
3. Oxidative Phosphorylation (production of ATP): Electron Transport and Chemiosmosis.
Glycolysis, which occurs in the cytosol, begins by breaking down glucose into two molecules of a compound called pyruvate.
The citric acid cycle, which takes place in the mitochondrial matrix, completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide.
In the third stage, the electron transport chain accepts electrons from the breakdown products of the first two stages and passes these electrons from one molecule to the other.
The energy released at each step of the chain is stored in a form the mitochondrion can use to make ATP.

4. Cellular Respiration theoretically produces 38 molecules of ATP

5. Stage 1 - Glycolysis
Glucose is split into two three carbon sugars. These smaller sugars are then oxidized to form two molecules of pyruvate.
You need to know that during glycolysis, a glucose molecule is broken down into two pyruvate molecules and 2 ATP are formed.

6. Stage 2 - The Krebs Cycle Also known as the Citric Acid Cycle.
What is it? It is a chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules to carbon dioxide; occurs within the mitochondrion; the second major stage in cellular respiration.
Upon entering the mitochondrion via active transport, pyruvate is first converted to a compound called acetyl coenzyme A, or acetyl CoA.

7. Short Summary
Acetyl CoA starts the Krebs cycle by joining with Oxaloacetate.
It is an 8 step process and involves the oxidization of several enzymes (NAD+ to NADH, FAD to FADH2, GDP to GTP and ADP to ATP.)
During a redox reaction, there is a loss of electrons (oxidization).
It occurs in the mitochondrial matrix of the cell.

8. Stage 3 – Oxidative Phosphorylation
The production of ATP using energy derived from the oxidation & reduction reactions of the electron transport chain.
Electron transport chain – a collection of molecules embedded in the inner membrane of the mitochondrion – known as the cristae. The cristae allow for a greater surface area for chemical reactions to occur. This is the part of cellular respiration that oxygen is used.
About 34 ATP are produced during stage 3, and are transported by active transport from the mitochondrial matrix back into the cytosol.

9. Conclusion!
Cellular respiration is the most prevalent and efficient catabolic pathway (a metabolic pathway that releases stored energy by breaking down complex molecules.) Oxygen is consumed as a reactant along with the organic fuel.
Mitochondria house most of the metabolic equipment for cellular respiration.
C6H12O6 + 6O2  6CO2 + 6H2O + Energy (38 ATP + heat)
The breakdown of glucose is exergonic; which means that energy is released in the form of heat.

10. The Big Picture – Aerobic Respiration
Cellular respiration, as we have talked about, occurs in the presence of oxygen. This is know as aerobic respiration.
The products of aerobic respiration are carbon dioxide, water, and ATP (as was shown on the previous slide.)
Oxygen is needed for aerobic respiration because it is the final acceptor in the electron transport chain; without it the process would stop.

11. The Big Picture – Anaerobic Respiration
Anaerobic respiration takes place in the absence of oxygen and occurs in two forms.
Lactic Acid Fermentation – Occurs in the cells of animals, particularly in the muscle tissue. Glucose is broken down into lactic acid and energy is released in the process. 2 molecules of ATP are produced during this process. Pain during exercise (a stitch) can be caused due to insufficient oxygen getting to the muscles and a build up of lactic acid.
Alcoholic Fermentation – Occurs in the cytoplasm of yeast cells. This also only produces 2 ATP molecules. An enzyme is used to break down the glucose molecules into carbon dioxide and alcohol. The carbon dioxide gas released during this process is what causes things, such as bread, to rise during baking.