Cellular Respiration and Fermentation

Cellular Respiration and Fermentation Chapter 7, Sections 5 and 6

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

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

Aerobic Respiration Occurs in 3 Stages: • Glycolysis • The Kreb’s Cycle • Electron Transport Chain and ATP Synthase

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 2 NADH Glucose → 2 Pyruvic Acid 2 ATP

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 CO2 and is converted into acetyl coenzyme A, or acetyl CoA 1 NADH 2 NADH Glucose → 2 Pyruvic Acid 2 Acetyl CoA 2 ATP 2 CO2

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

Stage Two – The Kreb’s Cycle (con’t) Acetyl CoA 3 NADH + 1 FADH2 KREB’SCYCLE ATP CO2 CO2 After 2 cycles, 6 NADH, 2 FADH2, 4 CO2, and 2 ATP molecules are produced

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

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 32-34 ATP molecules from ADP per original glucose molecule

ATP Synthase

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

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

ALCOHOLIC Pyruvic Acid → CO2 + ethyl alcohol Occurs in yeast CO2 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 Two Types of Fermentation

Cellular Respiration and Fermentation