Fermentation & Anaerobic Respiration Chapter

SECTION 9.5 Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen

With Oxygen = Aerobic When O 2 is present in the cell… Glycolysis  “prep” step  Krebs cycle  ETC

Without Oxygen = Anaerobic When no O 2 is present in the cell, glycolysis is followed by fermentation ◦ What is the evolutionary advantage of this? Pyruvate  Fermentation Regenerates NAD+ carriers to allow glycolysis to continue Plants undergo alcoholic fermentation Animals undergo lactic acid fermentation

Lactic Acid Fermentation Pyruvate → lactic acid + NAD + Human muscle cells when oxygen is low during exercise Lactic acid builds up in muscle tissue, causing soreness

Alcoholic Fermentation Pyruvate → CO 2 + alcohol + NAD + Used by microorganisms to make beer/wine Used by yeast to make bread ◦ CO 2 causes the “holes” in bread; why bread rises Facultative anaerobes ◦ Can switch back and forth between fermentation/respiration depending on O 2 availability

So why be able to do both? Isn’t aerobic CR better than fermentation?

Evolutionary Links Glycolysis = Most widespread metabolic pathway Earliest fossil bacteria (3.5 billion years ago) but large amounts of oxygen not present until 2.7 BYA Works without oxygen ◦ Suggests ancient prokaryotes probably used glycolysis to make ATP before oxygen was present Happens in cytoplasm without mitochondria ◦ Suggests it was in early prokaryotic cells before eukaryotes appeared ◦ Eukaryotes appeared 1 billion years after prokaryotes (endosymbiotic theory)

SECTION 9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways

Other Fuel Molecules Fats, proteins, and carbohydrates can be broken down to release energy ◦ 1g of fat  twice as much ATP as 1g of carbohydrate Beta oxidation of fats ◦ Breakdown of fatty acids into 2 carbon fragments that can enter the Krebs cycle as Acetyl CoA Protein is broken into amino acids ◦ Most used by cell to build protein ◦ Excess amino acids converted into intermediates of glycolysis and Krebs and enters respiration that way Carbohydrates broken down to monomers to fuel respiration