CELLULAR RESPIRATION

glucose + oxygen → carbon dioxide + water +ATP Cellular Respiration Cellular Respiration: Process by which mitochondria break down food molecules to produce ATP in plants and animals glucose + oxygen → carbon dioxide + water +ATP or C6H12O6 + 6O2→ 6CO2 + 6H2O +ATP Changes organic chemical energy (glucose) into inorganic chemical energy (ATP) There are three stages of Cellular Respiration Glycolysis Anaerobic – does not require oxygen Citric Acid (Krebs) Cycle Aerobic – does require oxygen Electron Transport Chain

Glycolysis Glycolysis: Breaks down glucose into two molecules of pyruvate (a colorless acid formed as an intermediate in metabolism) This reaction uses enzymes and takes place in the *cytoplasm* of the cell (anaerobic reaction) Produces: 2 pyruvate molecules (used in the next step of Cellular Respiration) 2 ATP molecules (energy the cell can use) 2 NADH (electron carrier similar to NADPH)

Into the Mitochondria… Before the next step of Cellular Respiration can occur, the pyruvic acid molecules must go into the *mitochondria* Two oxygen-dependent (aerobic) reactions: Citric Acid Cycle (or Krebs Cycle) and the Electron Transport Chain Pyruvate → carbon dioxide + water + ATP AEROBIC PART BEGINS!

Citric Acid/Krebs Cycle (see page 119 in your book) CO2 is released Pyruvate from Glycolysis fuels the cycle 4 CO2 is released NADH and FADH2 is released ATP is released

Citric Acid/Krebs Cycle Every turn yields 1 ATP, 4 NADH, and 1 FADH2 (on average); 3 CO2 (waste product) But it turns two times for every glucose molecule! So 2 ATP, 8 NADH, and 2 FADH2 ; 6 CO2 (waste)

Electron Transport Chain Electron Transport Chain uses the electron carriers (NADH and FADH2) to pass electrons down the protein chain and slowly release energy that is used to form ATP and water molecules Electron Transport Chain transfers the most energy of all the steps (32-34 ATP)

Cellular Respiration Equation C6H12O6 + 6O2 6CO2 + 6H2O + energy Carbon Dioxide – waste product of the Krebs/Citric Acid Cycle Water – released from Electron Transport Chain Glucose made in photosynthesis by plants or consumed by animals Used in Glycolysis ATP released from Glycolysis, Citric Acid Cycle, and Electron Transport Chain Oxygen from the atmosphereUsed in Electron Transport Chain Between 36-38 ATP can be made with this process. This ATP can be used by the cells for cellular metabolism.

Citric Acid Cycle/Krebs Cycle Electron Transport Chain Cellular Respiration ATP=2 Glycolysis Glucose 2 Pyruvic Acid CO2 Citric Acid Cycle/Krebs Cycle Pyruvic Acid ATP=2 NADH and FADH2 Water NADH and FADH Electron Transport Chain Oxygen ATP=32 Total ATP=36!!!

Fermentation When oxygen is not available anaerobic respiration, fermentation, can follow glycolysis INSTEAD in order to continue to produce energy. This is not as efficient as aerobic respiration and produces far fewer ATP’s Two types of fermentation: Lactic acid Fermentation Alcoholic Fermentation

Lactic acid Fermentation Lactic acid fermentation occurs in muscle cells during strenuous exercise when a lot of energy is required and oxygen is scarce (oxygen debt). Glucose → pyruvic acid → lactic acid + ATP The lactic acid is transferred from the muscle cells to the liver where it will be converted back into pyruvic acid The build up of lactic acid in the muscles is what causes them to be fatigued and sore.

Lactic Acid Fermentation In food… Often done by bacterial cells Yogurt Sauerkraut Kimchi – Korean dish; fermented vegetables

Alcoholic Fermentation Yeast and some bacteria cells are capable of alcoholic fermentation during which glucose is broken down to release CO2 and ethyl alcohol Glucose → pyruvic acid → alcohol + CO2 + ATP The bubbles formed by the CO2 make bread rise The alcohol released turns grape juice into wine