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 O 2 to produce ATP Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) In the absence of O 2, 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 + CO 2 + 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 CO 2 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 H + 2 CO 2 2 Ethanol 2 Acetaldehyde Alcohol fermentation
Lactic Acid Fermentation Pyruvate + NADH lactic acid + NAD + pyruvate is reduced to lactic acid (3-C compound); no CO 2 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 O 2 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 O 2
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 O 2 is present: Krebs and E.T.C. -if no O 2 is present: Fermentation
Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION 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 acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH 3 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
Inhibits Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate AMP Stimulates + Inhibits Pyruvate ATP Acetyl CoA Citrate Citric acid cycle Oxidative phosphorylation