Chapter 7 Section 2

1. Chapter 7 Section 2 Aerobic Respiration

2. The Role of the Mitochondria Aerobic respiration has the same goal as anaerobic respiration: to generate chemical energy in the form of ATP and regenerate NAD+. The mitochondria contains an inner membrane with structures designed to generate a lot of ATP. The inner folds called cristae are surrounded by a solution called the matrix.

3. Stage I - Glycolysis Glycolysis occurs in the cytoplasm and involves the breakdown of glucose into G3P then pyruvic acid. During this stage 2 net ATP are produced along with NADH that will be used in later reactions to provide H+ and electrons.

4. Stage 2 – Converting Organic to Chemical Energy This stage consists of four phases that involve a series of biochemical pathways that transforms the organic energy found in pyruvic acid to the chemical energy of ATP. During these steps both carbon dioxide and water are produced as waste products.

5. Stage 2 – Converting Organic to Chemical Energy The first phase is called the transition step. It involves transporting pyruvic acid into the matrix solution of the mitochondria. The pyruvic acid is then broken down into a 2 carbon molecule called acetyl-CoA. The CoA is a coenzyme that gets recycled. During the process 2 CO2 molecules and 2 NADH + H+ molecules are produced as well.

6. Stage 2 – Converting Organic to Chemical Energy The second phase also occurs in the matrix and is called the Kreb’sor Citric Acid Cycle. The purpose of this phase is to completely break down the organic energy in acetyl-CoA into chemical energy forms. Both ATP along with NADH + H+ and FADH2 are created. The cycle also releases CO2 as a waste product.

7. Stage 2 – Converting Organic to Chemical Energy The Kreb’s Cycle begins with the 2 carbon acetyl-CoA combining with a 4 carbon molecule called oxaloacetic acidto make a 6 carbon molecule called citric acid. The cycle continues with the conversion of citric acid to a 5 carbon molecule and the production of CO2 and NADH + H+.

8. Stage 2 – Converting Organic to Chemical Energy The 5 carbon molecule gets converted to a 4 carbon molecule so another CO2 and NADH + H+ is released. During this part of the cycle ADP combines with P to make ATP. Now all six of the original carbons in glucose have been converted to inorganic CO2.

9. Stage 2 – Converting Organic to Chemical Energy In the next step of the cycle the 4 carbon compound loses some hydrogen to produce another 4 carbon compound. The hydrogen bonds to FAD to produce FADH2 which is another chemical energy form very similar to NADH.

10. Stage 2 – Converting Organic to Chemical Energy The Kreb’s cycle is completed by the removal of more hydrogen from the 4 carbon compound to reform the oxaloacetic acid molecule. This step also produces NADH + H+. The cycle goes around twice because there are 2 acetyl-CoA molecules that need processed.

11. Stage 2 – Converting Organic to Chemical Energy All together the Kreb’s cycle yields 4 CO2 molecules, 6 NADH + H+ molecules, 2 FADH2 molecules and 2 ATP molecules. The NADH and FADH2 molecules will provide H+ and e- for the next set of reactions to generate a large amount of chemical energy.

12. Stage 2 – Converting Organic to Chemical Energy The third phase of Stage 2 involves several locations within the mitochondria. It starts with the breakdown of the NADH and FADH2 molecules in the matrix solution. These molecules provide electrons that enter an ETC in the cristae folds of the inner mitochondria membrane. The molecules also provide H+ that will be used to make chemical energy.

13. Stage 2 – Converting Organic to Chemical Energy The movement of the electrons along the ETC molecules provides energy to power the proton pump to move H+ out of the matrix. The H+ then passively diffuses through the ATP synthase back into the matrix. This allows ADP to combine with P to make ATP. The majority of the ATP made during aerobic respiration occurs in this step.

14. Stage 2 – Converting Organic to Chemical Energy The fourth phase of Stage 2 involves the acceptance of electrons and hydrogen ions to create a stable molecule. Oxygen molecules (O2) diffuse into the matrix and are split by an enzyme. Each oxygen atom now only has six valence electrons. Both oxygen atoms happily accept two electrons from the ETC molecules to gain stability.

15. Stage 2 – Converting Organic to Chemical Energy Electron movement in the ETC would stop if there was no where for the electrons to go at the end. The hydrogen ions also gain stability by bonding to the oxygen atoms. Two H+ bond to each O to form a water molecule. No enzyme is needed for this because all atoms are now more stable.

16. Stage 2 – Converting Organic to Chemical Energy Oxygen is not the only substance capable of accepting electrons during cellular respiration. Cyanide has a greater electron affinity (attraction for them) than oxygen. Cyanide does not bond to the H+ however, so the production of ATP stops and the organism suffocates on the cellular level.