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GLYCOLYSIS AND FERMENTATION CHAPTER 7 – CELL RESPIRATION OVERALL EQUATION C6H12O6 + 6O2 6CO2 + 6H2O + 36ATP HARVESTING CHEMICAL ENERGY • Cellular Respiration – The process in which cells make ATP by breaking down organic compounds • Cellular Respiration begins with Glycolysis: a biochemical pathway in which glucose is oxidized into pyruvic acid Organic Compounds ATP Glycolysis No Oxygen Fermentation Oxygen Aerobic Respiration ATP ANAEROBIC PATHWAYS: • Chemical reactions that occur without oxygen GLYCOLYSIS • Occurs in cytosol in 4 major steps: • Step 1: 2 phosphate groups are attached to glucose, forming a new 6-carbon compound • Phosphates break off ATP ADP GLYCOLYSIS • Step 2: The 6-carbon molecule is split into 2 3-carbon molecules of PGAL GLYCOLYSIS • The 2 PGAL molecules are oxidized (lose electron, becoming more positive), and each receives another phosphate group (each now has 2 phosphate groups attached). • A new 3-carbon molecule has been formed. • As PGAL is oxidized, 2 molecules of NAD+ are reduced to NADH GLYCOLYSIS • NAD+ an organic molecule that accepts electrons (reduced) during redox reactions GLYCOLYSIS • Step 4: The phosphate groups added in steps 1 and 3 are removed from the 3-carbon compounds, producing 2 molecules of pyruvic acid. Each phosphate group is combined with a molecule of ADP to make a molecule of ATP GLYCOLYSIS • Because 2 molecules of ATP were used in step 1, and 4 were produced in step 4, there is a gain of 2 molecules of ATP for each molecule of glucose that is converted into pyruvic acid. FERMENTATION • A process in which cells make a limited amount of ATP by converting glucose into another organic compound such as lactic acid or ethyl alcohol in the absence of oxygen • Two common fermentation pathways result in the production of lactic acid and ethyl alcohol. LACTIC ACID FERMENTATION • The process by which pyruvic acid is converted into lactic acid. • Involves the transfer of 2 hydrogen atoms from NADH and H+ to pyruvic acid. NADH is oxidized to NAD+ in the process. • The resulting NAD+ is used in glycolysis, where it is again reduced to NADH LACTIC ACID FERMENTATION • Lactic Acid Fermentation by microorganisms helps produce cheese and yogurt LACTIC ACID FERMENTATION • Also occurs in muscles during strenuous exercise. Muscles switch from aerobic respiration to lactic acid fermentation when they use more oxygen than they can take in. • Lactic acid builds up and causes sore muscles. • Eventually lactic acid diffuses into blood, returning to the liver. ALCOHOLIC FERMENTATION • Alcoholic Fermentation is used by some unicellular organisms (yeast) • Process by which pyruvic acid is converted to ethyl alcohol; anaerobic action of yeast on cells ALCOHOLIC FERMENTATION • Requires 2 steps • 1st – A CO2 molecules is removed from pyruvic acid, leaving a two-carbon compound. • 2nd - 2 hydrogen atoms (from NADH and H+) are added to the two-carbon compound to form ethyl alcohol ALCOHOLIC FERMENTATION • Used to make beer, wine, bread ENERGY YIELD • Kilocalories: a unit of energy. 1Kcal = 1000 calories • The complete oxidation of a standard amount of glucose releases 686 kcal of energy • The production of a standard amount of ATP from ADP absorbs 12 kcal of energy • Efficiency of glucose = Energy required to make ATP Energy released by oxidation of glucose 2 x 12 kcal 686kcal x 100% = 3.5% • 2 ATP molecules produced during glycolysis receive only a small percentage of the energy that could be released by the complete oxidation of each molecule of glucose • Most energy originally contained in glucose is still held in the pyruvic acid • Anaerobic pathways are not very efficient • The anaerobic pathway probably evolved early in the history of life on earth. • The first organisms were bacteria. They produced all their ATP through glycolysis. • It took over a billion years for the first photosynthetic organism to appear. The oxygen they released as a byproduct stimulated the evolution of organisms that make their ATP through aerobic respiration • Anaerobic pathways provide enough energy for many present day organisms like unicellular and very small multicellular organisms. • Larger organisms have much greater energy requirements that cannot be met with anerobic respiration must use aerobic respiration