NOTES: Ch 9, part & 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

● 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 Alcohol Fermentation

CO H + 2 NADH2 NAD + 2 Acetaldehyde 2 ATP 2 ADP + 2 P i 2 Pyruvate 2 2 Ethanol Alcohol fermentation Glucose Glycolysis

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 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 Lactic Acid Fermentation

+ 2 H + 2 NADH2 NAD + 2 ATP 2 ADP + 2 P i 2 Pyruvate 2 Lactate Lactic acid fermentation Glucose Glycolysis

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 = 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

Pyruvate Glucose CYTOSOL No O 2 present Fermentation Ethanol or lactate Acetyl CoA MITOCHONDRION O 2 present Cellular respiration 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

Citric acid cycle Oxidative phosphorylation Proteins NH 3 Amino acids Sugars Carbohydrates Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA Fatty acids Glycerol Fats

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

Citric acid cycle Oxidative phosphorylation Glycolysis Glucose Pyruvate Acetyl CoA Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate – Inhibits ATP Citrate Inhibits Stimulates AMP + –