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Glycolysis and Anaerobic Respiration Biology Exploring Life section 7.5-7.6 Modern Biology section 7-1 Glycolysis and Anaerobic Respiration • Objectives: • Describe the process of glycolysis in terms of its products and energy yield. • Explain why a fermentation pathway must be included with glycolysis in order for anaerobic respiration to occur. • Compare and contrast the fermentation pathways used by animal cells and yeasts. • Give examples of how both types of fermentation are used in industry. Anaerobic Respiration • What is anaerobic respiration? • Cellular respiration is the process by which living cells release the energy contained in food molecules. • Most of the ATP produced by cells uses a complex electron transport chain in which oxygen is the final electron acceptor. Because the process uses oxygen, it is called aerobic respiration. • When cells are forced to work without enough oxygen they can produce ATP and continue working for short periods by using other biochemical pathways (fermentation). • Some organisms (yeasts and some bacteria) can provide all their ATP requirements without the use of oxygen. • Biochemical pathways that release energy without the use of oxygen are collectively called anaerobic respiration. Anaerobic Respiration • How does anaerobic respiration produce ATP? • Anaerobic respiration uses glycolysis, the splitting of sugar molecules, to produce a small amount of ATP. – Glycolysis only extracts about 3.5% of the total energy available in a molecule of sugar. • This process is accomplished by various enzymes in the cytoplasm of the cell and does not require mitochondria or other cellular organelles. • Glycolysis is also the first stage of aerobic respiration so the products of the reaction can be further broken down by mitochondria to release more energy in aerobic respiration. Anaerobic Respiration • How does anaerobic respiration produce ATP? 1 1. Using two ATP molecules as activation energy, the cell splits a sixcarbon glucose molecule in half. The result is two three-carbon molecules of PGAL, each with one phosphate group. Anaerobic Respiration • 2 How does anaerobic respiration produce ATP? 1 3 2. Each three-carbon PGAL molecule then transfers electrons and hydrogen ions to a carrier molecule called NAD+.(very similar to NADP+ found in the light reactions of photosynthesis). Accepting two electrons and one hydrogen ion converts the NAD+ to a compound called NADH. 3. A second phosphate group is now added to each molecule of PGAL. Anaerobic Respiration • 2 How does anaerobic respiration produce ATP? 1 3 4 4. Both phosphate groups added to each 3-carbon molecules are now removed and used to convert 2 ADP molecules to ATP. The resulting 3-carbon molecule is pyruvic acid. The end result is that four new ATP molecules are produced, a net gain of two ATP molecules. Fermentation Pathways • What is fermentation? • The products of glycolysis can be further broken down without the use of oxygen through additional biochemical pathways that occur in the cytosol. • The combination of glycolysis pulse these additional pathways is called fermentation. • Fermentation does not produce any additional ATP but it does regenerate NAD+ which is used to keep glycolysis going. NAD+ is the final electron acceptor for glycolysis. Without a constant supply, the process would stop. Fermentation Pathways • Lactic acid fermentation: • This is a fermentation pathway that occurs in the cells of animals and some microorganisms. • In this process two hydrogen atoms provided by NADH and H+ ions are transferred to pyruvic acid converting it to lactic acid. • The NADH is oxidized (loses an electron) to become NAD+ which is used to power glycolysis. Fermentation Pathways • Alcoholic Fermentation: • • • • This is a fermentation pathway that occurs in the cells of yeasts and some microorganisms. In this process, a CO2 molecule is removed from each pyruvic acid molecule and released as a gas. Two hydrogen atoms provided by NADH and H+ ions are transferred to the two carbon molecule converting it to ethyl alcohol. The NADH is oxidized (loses an electron) to become NAD+ which is used to power glycolysis. Fermentation Pathways • Industrial uses of fermentation pathways: • Fermentation carried out by microorganisms is a part of many modern manufacturing processes. • Lactic acid fermentation: – Microbes to transform milk into cheese and yogurt. – The sharpness or sour flavor of yogurt and some cheeses is mainly due to lactic acid. – Microbial fermentation turn soybeans into soy sauce and cabbage into sauerkraut. – Microbial fermentation is used in the treatment of waste water to help break down solid waste into sludge which is used for fertilizer. Fermentation Pathways • Industrial uses of fermentatio n pathways: • Fermentation carried out by microorganisms is a part of many modern manufacturing processes. • Lactic acid fermentation: Fermentation Pathways • Industrial uses of fermentati on pathways: Barley Malt (sprouted grain) • Fermentation carried out by microorganisms is a part of many modern manufacturing processes. • Alcoholic fermentation: – Used to make alcoholic beverages such as beer and wine. – The carbon dioxide is what makes champagne and beer bubbly. Copper “Pot Still” Barley Malt and Grist Mash (fermentation) Fermentation Pathways • Industrial uses of fermentati on pathways: • Fermentation carried out by microorganisms is a part of many modern manufacturing processes. • Alcoholic fermentation: – Carbon dioxide bubbles from baker's yeast make bread rise. Fermentation Pathways • Fermentation carried out by microorganisms is a part of many modern manufacturing processes. • Alcoholic fermentation: – Alcoholic fermentation of bio-matter such as corn stalks and processed sugar cane is used to make ethanol which is fuel for cars. Video Resources • Bozeman Science – Anaerobic respiration • Brightstorm! Science Help – Anaerobic respiration • Khan Academy – Anaerobic respiration