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Fermentation Do Now 12/18 (HW check 6.7-6.9) OBJECTIVES: 1. Define oxidation, reduction, and redox; explain how these reactions occur in metabolism. 2. Describe the processes of ethanolic and lactic acid fermentation. TASK: 1. There is a total of about 3,000 kJ of energy stored in the bonds of one glucose molecule. When a cell hydrolyzes ATP to ADP, about 50 kJ of energy is released. What is the approximate energy efficiency (%) of glycolysis? Redox Reactions Redox: LEO the Lion Says GER. • The Loss of Electrons is Oxidation; the Gain of Electrons is Reduction. • Whenever something is oxidized, something else must be reduced (i.e. the electrons have to go somewhere!) • In fermentation, NADH is oxidized, and pyruvate is reduced. Adding Oxygen to Carbon Releases Energy • Respiration oxidizes carbon; the more the carbon gets oxidized, the more energy is released. Compound Carbon is H:O Ratio Amount of energy stored in molecule CH4 Fully Reduced 4:0 High C6H12O6 (Glucose) C3H4O3 (Pyruvate), C2H4O (Ethanol), C3H6O3 (Lactic Acid) Partially oxidized 4:1 – 4:3 Moderate CO2 Fully Oxidized Low 0:4 Lactic Acid Fermentation – you do this! Notice: No CO2 produced. NADH is oxidized to NAD+ Pyruvate is reduced to lactic acid. Fermentation: To recycle NAD+ The top section is glycolysis. The bottom is ethanolic fermentation. Alcoholic Fermentation Ethanol and CO2 are the waste products Fermentation is Wasteful • The products of fermentation (ethanol or lactic acid) contain MORE energy than pyruvate! • The NADH used loses valuable energy – in anaerobic conditions anyway. So Why Do They Do it? • The electrons ripped from food have to go somewhere! • In aerobic respiration they eventually end up in water after being attached to oxygen. • When there’s no oxygen around, the cell deposits the electrons on what’s available: the leftovers from glycolysis. • This is ONE of the ways in which aerobic respiration is more efficient than anaerobic. Yummy Yummy Fermentation • In addition to making lots of yummy food products from soy sauce to kimchi, fermentations done by engineered microbes can produce useful enzymes or drugs! Other Notable Types of Fermentation Recap • Fermentation is the second step in anaerobic respiration; its function is to recycle the NAD+ needed for glycolysis to continue. • Alcoholic fermentation (like done by yeast) produces CO2 and ethanol. Lactic acid fermentation (like done by human muscle cells) produces lactic acid. There are many other types as well. • Fermentation is inefficient: the waste products of glycolysis are REDUCED by NADH, which adds chemical energy to them.