NOTES: Ch 9, part 4 - 9.5 & 9.6 - Fermentation & Regulation of Cellular Respiration 9.5 - Fermentation enables some cells to produce ATP without the use of oxygen ● Cellular respiration requires O2 to produce ATP ● Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions) ● In the absence of O2, glycolysis couples with fermentation to produce ATP Alternative Metabolic Pathways - Vocabulary: ● aerobic: existing in presence of oxygen ● anaerobic: existing in absence of oxygen ● FERMENTATION = anaerobic catabolism of organic nutrients Types of Fermentation ● Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis ● Two common types are alcohol fermentation and lactic acid fermentation Alcohol Fermentation + Pyruvate + NADH ethanol + CO2 + NAD ● pyruvate is converted to ethanol ● NADH is oxidized to NAD+ (recycled) ● performed by yeast and some bacteria Alcohol Fermentation ● In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 ● Alcohol fermentation by yeast is used in brewing, winemaking, and baking 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ 2 Ethanol 2 Acetaldehyde Alcohol fermentation Lactic Acid Fermentation Pyruvate + NADH lactic acid + NAD+ ● pyruvate is reduced to lactic acid (3-C compound); no CO2 produced ● NADH is oxidized to NAD+ (recycling of NAD+) Lactic Acid Fermentation ● Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt ● Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate 2 Lactate Lactic acid fermentation Fermentation and Cellular Respiration Compared: ● Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate ● in fermentation, NADH is recycled back to NAD+ ● in fermentation, final electron acceptor is pyruvate, not O2 Fermentation and Cellular Respiration Compared: ● amount of energy harvested: Fermentation = 2 ATP Cellular respiration = 36-38 ATP ● oxygen NOT required for fermentation ● Obligate anaerobes: only grow in absence of oxygen (e.g. clostridium botulinum) ● Obligate aerobes: only grow in presence of oxygen Micrococcus luteus ● Facultative anaerobes: can grow in either presence or absence of oxygen (e.g. yeast or bacteria that make yogurt, cheese; our muscle cells at the cellular level) *in a faculatative anaerobe, pyruvate is a “fork” in the metabolic road which leads to 2 alternate catabolic routes: -if O2 is present: Krebs and E.T.C. -if no O2 is present: Fermentation Glucose CYTOSOL Pyruvate No O2 present O2 present Fermentation Cellular respiration MITOCHONDRION Ethanol Acetyl CoA or lactate Citric acid cycle The Evolutionary Significance of Glycolysis ● Glycolysis occurs in nearly all organisms ● Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere 9.6 - Glycolysis and the Krebs cycle connect to many other metabolic pathways ● Gycolysis and the Krebs cycle are major intersections to various catabolic and anabolic pathways The Versatility of Catabolism ● Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration ● Glycolysis accepts a wide range of carbohydrates ● Proteins must be digested to amino acids; amino groups can feed glycolysis or the Krebs cycle ● Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) ● An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate Proteins Carbohydrates Fats Amino Sugars Glycerol Fatty acids acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation Biosynthesis (Anabolic Pathways) ● The body uses small molecules to build other substances ● These small molecules may come directly from food, from glycolysis, or from the Krebs cycle Regulation of Cellular Respiration via Feedback Mechanisms ● FEEDBACK INHIBITION is the most common mechanism for control ● If ATP concentration begins to drop, respiration speeds up; ● when there is plenty of ATP, respiration slows down ● Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway Glucose AMP Glycolysis Fructose-6-phosphate Stimulates + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylation.