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Cellular Respiration: Harvesting Chemical Energy A. P. Biology Chapter 9 Mr. Knowles Liberty Senior High School How is burning a candle like a respiring cell? So why don’t we just burn sugar? It’s all about capturing energy! Different Strokes for Different Folks! • Autotrophy- “self-feeding,” when organisms use energy from light and CO2 to synthesize organic molecules. • Heterotrophy- “other-feeding,” use already made organic molecules obtained from other organisms, living or dead. Oxidative Respiration C6H12O6 + 6O2 --> 6CO2 + 6H2O + ENERGY (ATP) 720 kcal of energy /mole glucose at cell conditions Oxidative Respiration • Catabolism of glucose into carbon dioxide and water, releasing 720 kcal/mol glucose. • Is a Four Step Process = Glycolysis + Oxidation of Pyruvate + Krebs Cycle + Electron Transport Chain Oxidative Respiration • Redox reaction that releases energy by repositioning electrons closer to oxygen atoms. • Uses ATP to trap energy and + + NAD and FAD to transport electrons. ATP is the Energy Currency of the Cell Adenosine Triphosphatestores ~12kcal/mol Adenine PO4 PO4 PO4 Deoxyribose Oxidative Respiration • Energy is harvested from glucose in a series of gradual + steps, using NAD as an electron carrier. 1. Glycolysis • Occurs with or without oxygen. • Two Step Process: Modifying Glucose (Steps 14) Removing Groups that Provide Energy (Steps 5 -9). Making ATP During Glycolysis • Substrate-level Phosphorylation transferring PO4 directly to ADP --> ATP. • Kinases- phosphorylates, adds PO4 group to a substrate. Ex. Hexokinase Each Step Uses a Specific Enzyme • Isomerases- change substrates into isomers. Ex. Glucose-->Fructose, Phosphoglucoisomerase. Each Step Uses a Specific Enzyme • Dehydrogenasesoxidizes substrates. Ex. G3PDH At the End of Glycolysis! + NAD • Glucose + 2 ADP + 2 Pi + 2 -> 2 Pyruvate + 2 ATP + 2 NADH + 2H+ + 2 H20 • Each ATP = 12 kcal/mole of energy. • Inefficient capture of energy, only 3.5 % of available energy in glucose. • Most remains in pyruvate. What would a food chain look like if organisms could only perform glycolysis? Are they alive today? Answer: The Archaebacteria 3.5 billion years ago and TODAY! 2nd Order Heterotroph? 1st Order Heterotroph ? Autotrophs Glycolysis ONLY 3.5% Efficiency Without Kreb’s and ETC… • Food chains were not very complex; few trophic levels. • Could support very few animals with such poor efficiency. 2. Oxidation of Pyruvate + NAD • Pyruvate + + CoA --> Acetyl-CoA + NADH • Acetyl-CoA can now enter the third step-Krebs Cycle. 3. Krebs Cycle • Oxidation of Acetyl-CoA. • Produce 2 ATP by substrate-level phosphorylation. • Many electrons harvested for the 4th Step (Electron Transport Chain). • 6 NADH + 2 FADH • All that remains of the glucose is 6 CO2. 4. Electron Transport Chain • Convert the energy from the NADH and FADH made in the first three steps and make ATP. • A series of transfers from transmembrane proteins that are progressively more oxidative. • Eventually tranferred to oxygen --> reducing it to water. FADH2 H + FAD+ 4H+ 2H2O Animation of Electron Transport Chain ATP Synthase Finally, ATP!!!!! Factors that Affect Aerobic Respiration • Respiration Rate- How much O2 can be taken in? • Activity Level. • Size of the Organism. • Age and Gender. • Ectothermic vs. Endothermic Organisms Ectotherms Have Slow Metabolisms Are there options to aerobic respiration? Anaerobic Respiration (Fermentation)- without oxygen. What process can you do without oxygen? Without Oxygen… • Living cells can only make ATP by glycolysis. • Only 2 ATP/molecule of glucose. + • May run out of NAD . Two Kinds of Fermentation • Alcoholic Fermentation- converts pyruvic acid (from glycolysis) and converts it into: 1. CO2, 2. Ethyl alcohol, + 3. NAD • Replaces NAD+ so glycolysis can continue. Alcoholic Fermentaion Let’s ferment? Demo: Home made wine! Fermentation in a Whale! Show me Lactic Acid Fermentation! Lactic Acid Fermentation NADH (H+) H3C--C—C--OH O O Pyruvic Acid NAD+ H H3C--C—C—OH OH O Lactic Acid Lactic Acid Fermentation • Converts pyruvic acid (from glycolysis) into two products: 1. Lactic Acid + 2. NAD + • Replaces NAD so glycolysis can continue. So now what? What do we do with all of the lactic acid after anaerobic respiration? The Cori Cycle, pp. 976977. Ch. 44 (old text) After Prolonged Exercise… • O2 consumption remains high. • Extra O2 is called Oxygen Debt. • Some of the O2 is used to convert Lactic Acid CO2 + H2O + ATP (brain, heart, some muscle). • Some of the O2 is used to convert Lactic Acid Glucose (Cori Cycle). Cori Cycle Anaerobic Glycogen The Two Fates of Lactic Acid • With O2 (aerobic conditions): 1. Brain, heart and some muscle fibers can convert it into ATP. 2. Liver can convert into glucose by the Cori Cycle. Hunters and Lactic Acid Build Up! Video: Built for the Kill- Swamp a hunting cormorant. Without Oxygen No O2 Alcoholic Fermentation Lactic Acid Fermentation Metabolism in an Ectotherm! Lactic Acid in a Crocodile Video: National GeographicSupercroc Other sources of energy! Proteins and Fats! Primary Structure Preparing Amino Acids for Metabolism Deamination H2N To Glycolysis or Kreb’s A Glycerol Three Fatty Acids Energy from Fat C C C-C-C-C-C-C-C-C C-C-C-C-C-C-C-C C C-C-C-C-C-C-C-C Glycerol 3 Fatty Acids Pyruvate Beta Oxidation Beta Oxidation • The catabolism of fatty acids. • The breakdown of fatty acids into 2-carbon pieces. (Acetyl groups). Beta Oxidation C-C-C-C-C-C-C-C (Fatty Acid) ATP ADP + Pi C-C-C-C-C-C NAD+ + FAD+ NADH + FADH C-C (Acetyl) Coenzyme A C-C-CoA (Acetyl CoA) Kreb’s Cycle What happens to the respiration rate if you limit the number of calories? Video: Scientific Frontiers-Never Say Die (Calorie Restriction)