Unit 1: Metabolic Processes Chapter 2: Cellular Respiration

1. Unit 1: Metabolic ProcessesChapter 2: Cellular Respiration

2. 2.1 Cellular Respiration: The Big Picture Photoautrophheterotrophchemoautotroph

3. Overview of Cellular Respiration

4. Process of Cellular Respiration • Glycolysis – 10 steps breaking down glucose to pyruvate (in cytoplasm) • Pyruvate Oxidation – 1 step occurring in the mitochondria matrix • Krebs Cycle (tricarboxylic acid cycle, the TCA cycle, or the citric acid cycle) – 8 steps occuring in the mitochondria matrix • Electron transport and chemiosmosis (oxidative phosphorylation) – many steps occurring in inner mitochondrial membrane

5. Mitochondria: convert the potential energy of food molecules into ATP.

6. an outer mitochondrial membrane encloses the entire structure • an inner mitochondrial membrane encloses a fluid-filled matrix • between the two is the intermembrane space • the inner membrane is elaborately folded with shelflike cristae projecting into the matrix.

7. The outer membrane contains many integral membrane proteins that form channels through which a variety of molecules and ions move in and out of the mitochondrion. • The inner membrane contains complexes of 5 integral membrane proteins that form the electron transport chain • The matrix contains a mixture of soluble enzymes that catalyze the breakdown of pyruvate. This series of enzymatic reactions is the Kreb's cycle.

8. OVERALL CHEMICAL EQUATION: 1. Many enzymes, co-enzymes, and intermediate chemicals are involved. 2. It is not a one-step process. Many reactions occur to release energy in small amounts.

9. Oxidation-Reductions reactions: • Glucose is broken down in a series of chemical steps during cellular respiration. Each reaction requires a specific enzyme • At several points in this biochemical pathway, oxidation-reduction reactions occur. One compound will be oxidized (lose electrons/hydrogens) and another will be reduced (gain electrons/hydrogens) • Co-enzymes such as NAD and FAD acts as electron/hydrogen acceptors. They will shuttle the energy of the electrons to another part of the process.

11. Nicotinamide Adenine Dinucleotide (NAD+)

12. In being reduced, NAD can accept two electrons, but only one proton. The other proton goes into solution as a hydrogen ion.

13. Flavin Adenine Dinucleotide (FAD)

14. The coenzymes gain energy when they gain electrons (are reduced). • This is a temporary state. In another series of reactions, the coenzymes give up the electrons (and thus the energy) and return to their oxidized state. • The energy they transfer is used to make ATP.

15. Methods of forming ATP • Substrate-Level Phosphorylation - the direct transfer of a phosphate group from a substrate to ADP to make ATP • Oxidative phosphorylation - the production of ATP using energy derived from the transfer of electrons in an electron transport system. This is an indirect method and occurs by chemiosmosis. • Chemiosmosis - the production of ATP utilizing the kinetic energy released when H+ flow through the ATP synthase complex

16. Substrate level phosphorylation-requires a substrate-enzyme-direct transfer of a Pi

17. GLYCOLYSIS • IN CYTOSOL • ONE OF THE OLDEST PATHWAYS: all life on earth performs glycolysis • DOES NOT REQUIRE OXYGEN (ANAEROBIC)

18. Glucose Activation: In the first step, a phosphate group from ATP is attached to glucose. This increase the energy level of glucose

19. This step is an isomerization

20. This is the second phosphorylation. At this point, 2 ATP molecules have been USED.

21. In this step, the glucose molecule is split into two three carbon molecules. DHAP undergoes isomerization to G3P. Why???

22. In this reaction, G3P is phosphorylated by inorganic phosphate groups in the cytosol. It is also oxidized: a hydrogen and 2 electrons are used to reduce NAD to NADH.

23. Substrate level phosphorylation!!! Formation of 2 ATP.

24. 2 Isomerization 2

25. 2 Phosphoenol pyruvate is also known as PEP 2

26. Substrate level phosphorylation: formation of two ATPs Pyruvate is called Pyruvic acid when it is written in the COOH form. The terms are used interchangeably.

27. Glycolysis Balance sheet: • For each pyruvate molecule produced by glycolysis, 2 ATP are formed  a total of 4ATP from one glucose molecule. • Since 2 ATP are used to energize the glucose in the first step, there is a net output of 2 ATP molecules. • Some energy is bound in 2 molecules of NADH + H+ and will be released in the electron transport chain to form ATP.

30. What raw materials are necessary for a cell to produce a molecule of ATP by substrate-level phosphorylation? • ADP • Pi (or a phosphate-containing intermediate from glucose) • A substrate enzyme

31. A) In eukaryotic cells, where does glycolysis occur?B) What does glycolysis mean? • In the cytoplasm. • The breaking of the glucose molecule into two pyruvate molecules

32. 4. • List the final products of glycolysis. • What two products of glycolysis may be transported into mitochondria for further processing? • 2 pyruvate, 4 ATP, 2 NADH, 2H+, and 2 ADP • Pyruvate and NADH

33. #6. How do ATP and ADP differ in structure and free energy content? • ADP has 2 inorganic phosphate groups attached to an adenosine molecule, whereas, ATP has 3. • ATP has 31 kJ/mol more potential energy than ADP

34. PYRUVATE OXIDATION • The PYRUVATE molecules produced by glycolysis enter the mitochondria by active transport. • Pyruvate oxidation occurs in the matrix (inner membrane?) of the mitochondria.

35. Pyruvate dehydrogenase complex • Pyruvate oxidation is carried out by a very large enzyme complex, the pyruvate dehydrogenase complex, which is located in the mitochondrial matrix. • The complex is comprised of three separate enzymes involved in the actual catalytic process, and uses a total of five different cofactors. • This reaction is irreversible, and is tightly regulated

37. PYRUVATE OXIDATION

39. The process of converting pyruvate to acetyl-CoA is anoxidative decarboxylation. • First, the pyruvate is oxidized (it goes from 3C to 2C acetyl.) CO2 is released as a result). • Secondly, NAD+ is reduced to NADH + H+ • Thirdly, the 2-carbon acetyl group combines with coenzyme A to form acetyl-CoA. • This acetyl-CoA entersthe Kreb's cycle.

40. Krebs Cycle Sir Hans Krebs, who won a Nobel Prize for its discovery, preferred the term “Tricarboxylic Acid Cycle” (TCA cycle)

44. Stage 3: The Krebs Cycle • A 2-carbon acetyl-CoA molecule is combined with a 4-C compound called oxaloacetate to produce a 6-C citrate molecule. • These citrate molecules are then oxidized to a 5-C -ketoglutarate. Carbon dioxide and NADH are produced. • -ketoglutarate molecules are then further oxidized to a 4-C succinyl Co-A compound. Carbon dioxide and NADH are produced. • The 4-C succinyl Co-A is then modified to succinate. GTPis produced by substrate level phosphorylation. It is converted to ATP.

45. The 4 carbon succinate molecule is oxidized to fumarate. FADH2is produced. • Fumarate is hydrated to malate. • Malate is oxidized to oxaloacetate. NADH is produced. • And the cycle starts again.

46. Note: • Each of the 3 carbon atoms present in the pyruvate that entered the mitochondrion leaves as a molecule of carbon dioxide (CO2) • At 3 steps in the cycle, a pair of electrons (2e-) is removed and transferred to NAD+ reducing it to NADH + H+ • At one step, a pair of electrons is removed from succinate and reduces FAD to FADH2

47. Summary of Kreb's cycle: • 2 carbon dioxide molecules are released, • 3 NADH are produced, • 1 FADH2 is produced • 1 molecule of ATP is formed • 1 molecule of water is used • molecule of oxaloacetate is left to start the cycle all over again.

48. Remember, there are 2 molecules of pyruvate formed from each molecule of glucose, therefore the cycle runs twice for each glucose molecule. • Almost all the chemical energy extracted from the pyruvate is carried by the hydrogen and temporarily transferred to the reduced coenzymes.

50. Describe the function of NAD+ and FAD in cellular respiration. • They act as coenzymes that harvest energy from the reactions of glycolysis, pyruvate oxidation, and the Krebs cycle and carry it to power ATP synthesis by oxidative phosphorylation.