FERMENTATION
Calling all NAD+ please! Glycolysis allows organisms to obtain energy from nutrients in the absence of oxygen Step 6 in the glycolytic pathway reduces NAD+ to NADH However, cells possess a limited supply of NAD+ If glycolysis continues without a mechanism to oxidize NADH back to NAD+, step 6 would be blocked and glycolysis would STOP In aerobic respiration, the ETC oxidized NADH allowing glycolysis to continue
Oh give me another way… Organisms have several ways of recycling NAD+ and allowing glycolysis to continue when oxygen is not available One method involves the transfer of the hydrogen atoms of NADH to certain organic molecules instead of the ETC This process is known as fermentation
Fermentation Eukaryotes use 2 methods of fermentation Ethanol fermentation Lactic acid (lactate) fermentation
Ethanol Fermentation
Ethanol Fermentation: The Process Some bacteria, yeast, mold, etc. NADH from glycolysis passes its hydrogen atoms to acetaldehyde, a compound formed when CO2 is removed from pyruvate by pyruvate decarboxylase Acetaldehyde is reduced to form ethanol, oxidizing NADH to NAD+ so it can return back to glycolysis and glycolysis can continue
Ethanol Fermentation The 2 ATP molecules produced in glycolysis satisfy the organisms energy needs and the ethanol and CO2 are released as waste products Humans use these waste products to produce breads, pastries, wine, beer, liquor, etc.
Lactic Acid Fermentation
Lactic Acid Fermentation During strenuous exercise, muscles respire glucose faster than oxygen can be supplied Under these conditions, oxidative respiration slows down and lactic acid fermentation begins
Lactic Acid Fermentation: The Process NADH produced in glycolysis transfers its hydrogen atoms to pyruvate This produces lactic acid and regenerates NAD+ Lactic acid is transported through the blood stream from the muscles to the liver When vigorous exercise ceases the lactic acid is oxidized back to pyruvate which will again start aerobic respiration
Homework Section 4.4 p. 190-194 Answer p. 194 1-4, 7, 8