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 is converted to ethanol 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

Alcohol fermentation 2 ADP + 2 P 2 ATP Glucose Glycolysis 2 Pyruvate 2 NADH 2 CO2 + 2 H+ 2 Acetaldehyde 2 Ethanol 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

Lactic acid fermentation 2 ADP + 2 P 2 ATP i 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 aerobes: only grow in presence of oxygen ● 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 Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA 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

Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty 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

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