The Krebs CycleBiology 11 Advanced

http://www.schooltube.com/video/22af9fa0535847978a08/

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 the degradation process 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.

Cellular Respiration theoretically produces 38 molecules of ATP

• Glucose, a six carbon sugar, is split into two three carbon sugars. These smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate (pyruvate is the ionized form of pyruvic acid.)

• You need to know that during glycolysis, a glucose molecule is broken down into two pyruvate, or pyruvic acid, molecules and 2 ATP are formed.

Stage 1 - Glycolysis

• Also known as the Citric Acid Cycle/Tricarboxylic 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.

Stage 2 - The Krebs Cycle

8 Steps of the CAC1. Acetyl CoA adds its two-carbon acetyl group to oxaloacetate,

producing citrate.

2. Citrate is converted to its isomer by the removal of one water molecule and addition of another.

3. Citrate loses a CO2 molecule, and the resulting compound is oxidized, reducing NAD+ to NADH.

4. Another CO2 is lost, and the resulting compound is oxidized, reducing NAD+ to NADH. The remaining molecule is then attached to coenzyme A by an unstable bond.

5. CoA is displaced by a phosphate group which is transferred to GDP, for GTP, and then to ADP, forming ATP.

6. Two hydrogens are transferred to FAD, forming FADH2 and oxidizing succinate.

7. Addition of a water molecule rearranges bonds in the substrate.

8. The substrate is oxidized, reducing NAD+ to NADH and regenerating oxaloacetate.

http://www.youtube.com/watch?v=juM2ROSLWfw

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter7/how_the_krebs_cycle_works.html

http://www.npr.org/blogs/krulwich/2011/09/14/140428189/lord-save-me-from-the-krebs-cycle

• Acetyl CoA starts the Krebs cycle by joining with Oxaloacetate.

• It is an 8 step process and involves the oxidization of 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.

Short Summary

Stage 3 – Oxidative Phosphorylation

• The production of ATP using energy derived from the oxidation & reduction reactions of the electron transport chain; during oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis.

• 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.

• Chemiosmosis – The process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work, such as the synthesis of ATP.

• About 34 ATP are produced during stage 3, and are transported by active transport from the mitochondrial matrix back into the cytosol.

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.

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.

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 relesed during this process is what causes things, such as bread, to rise during baking.