1 Cellular Respiration and Fermentation Chapter 7, Sections 5 and 6

2 The Cellular isms Metabolism: is the set of chemical reactions that occur in living organisms in order to maintain life. – These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. – Usually divided into two categories. Catabolism and Anabolism − Catabolism: breaking down & releasing energy − Anabolism: building up & requires energy

3 A Metabolic Pathway called Cellular Respiration Cells harvest energy by breaking bonds and shifting electrons from one molecule to another. – aerobic respiration - final electron acceptor is oxygen – anaerobic respiration - final electron acceptor is a molecule other than oxygen

4 Aerobic Respiration Occurs in 3 Stages: 1. Glycolysis 2. The Kreb’s Cycle 3. Electron Transport Chain and ATP Synthase

5 Stage One - Glycolysis Occurs in the cytoplasm For each molecule of glucose that passes through glycolysis, the cell nets 2 ATP molecules and 2 pyruvic acid molecules NADH carries 2 high energy electrons Glucose →2 Pyruvic Acid 2 NADH 2 ATP

6 Stage Two – The Kreb’s Cycle Occurs in the matrix of the mitochondrion where the needed enzymes are dissolved As pyruvic acid diffuses into the mitochondrion, each 3C molecule loses a molecule of CO 2 and is converted into acetyl coenzyme A, or acetyl CoA Glucose →2 Pyruvic Acid 2 NADH 2 ATP 2 Acetyl CoA 1 NADH 2 CO 2

7 Stage Two – The Kreb’s Cycle (con’t) Acetyl CoA is oxidized in a series of reactions Named after biologist Hans Krebs who first explained the steps in the 1930s

8 6-carbon Molecule 5-carbon Molecule 4-carbon Acceptor Stage Two – The Kreb’s Cycle (con’t) KREB’S CYCLE CO 2 Acetyl CoA 3 NADH + 1 FADH 2 After 2 cycles, 6 NADH, 2 FADH 2, 4 CO 2, and 2 ATP molecules are produced ATP

9 Stage Three: The Electron Transport Chain NADH molecules carry electrons to the inner mitochondrial membrane, where they transfer electrons to a series of membrane- associated proteins (electron carriers). Eventually the electrons are pulled towards OXYGEN and combine with hydrogen ions, forming water

10 Stage Three: ATP Synthase Action The ATP released in the ETC is used to move H+ ions across the membrane from low to high concentrations This stores potential energy (positive side vs negative side) ATP synthase is a protein in the membrane that spins like a mini turbine as H+ ions flow back across the membrane The spinning ATP synthase generates ATP molecules from ADP per original glucose molecule

11 ATP Synthase

12 Adding up the ATP from Cellular Respiration Mitochondrion Glycolysis Glucose 2 Pyruvic acid 2 Acetyl- CoA Krebs Cycle Electron Transport Maximum ATP per glucose: ATP Synthase

13 Harvesting Energy WITHOUT Oxygen If oxygen is not available to capture the 2 low energy electrons at the end of the ETC, the Kreb’s cycle and the ETC will stop producing ATP Glycolysis will continue to generate 2 ATP molcules, 2 NADH, and 2 Pyruvic Acid molecules NADH reacts with the pyruvic acid, making NAD+ available to carry electrons so glycolysis can continue making ATP

14 Two Types of Fermentation ALCOHOLIC Pyruvic Acid → CO 2 + ethyl alcohol Occurs in yeast CO 2 makes dough rise and bubbles in beer & champagne Ethyl alcohol makes alcoholic beverages LACTIC ACID Pyruvic Acid → Lactic Acid Occurs in muscles during vigorous exercise (can feel “burn”) Occurs in prokaryotes used to make cheese, yogurt, sour cream, and sauerkraut