1. Fermentation and Respiration Embden-Meyerhof (glycolysis) Fermentation products Respiration and electron transport Electron-transport phosphorylation Citric acid cycle Energy production from fermentation and respiration Alternate modes of energy generation

2. Overview of fermentation

3. Preparatory reactions for glycolysis Refer to figure 4.32 (p. 119) Preparatory reactions add phosphates (from ATP) –Fructose(1,6)diphosphate is the common intermediate for hexose fermentation –Two phosphates needed so that after splitting, each 3-carbon unit is ionized

4. Oxidation Reactions After splitting 6-carbon fructose into two 3-carbon glyceraldehyde-3-phosphate Key reaction: oxidation (NAD) plus phosphorylation yields 1,3-diphosphoglycerate Phosphoryl transfer to ADP, making ATP Isomerization yields phosphoenol pyruvate Phosphoryl transfer (ATP) from phosphoenol pyruvate yields pyruvate

5. Fermentation Reactions Electrons from NADH must be passed on Homolactic fermentation (muscles; most lactic- acid bacteria) –Simplest fermentation –pyruvate is reduced to lactate Alcoholic (yeasts; uncommon in bacteria) –Pyruvate + NADH -> *acetaldehyde + CO 2 + NADH - > ethanol + CO 2 In any fermentation, products must balance reactants (C, H, O); C 6 H 12 O 6 -> 2 x C 3 H 6 O 3

6. Phosphoroclastic Reaction This reaction is not a balanced fermentation –Pyruvate + NADH -> acetyl-CoA + HCOOH + NADH -> acetate + CO 2 + H 2 + NADH (phosphoroclastic reaction) –Must be coupled with another, NADH-consuming, reaction –Acetyl-CoA is transferred to phosphate (acetyl phosphate), and the phosphate is then transferred to ADP, making ATP and acetate –This reaction provides an extra ATP, but doesn’t dispose of extra electrons (NADH) from early oxidation reactions

7. Reduction of Pyruvate Reduction reactions must balance phosphoroclastic reactions Ethanol production (4-electron reduction [or 2NADH] of acetate) –Pyruvate + 2NADH -> acetate + HCOOH + 2NADH -> ethanol + HCOOH + NAD + –2 pyruvate + 2NADH -> acetate + ethanol + 2HCOOH + 2NAD + + ATP –This is a dominant reaction of the mixed acid fermentation (enteric bacteria such as Escherichia coli)

8. Gas Production in the Mixed Acid Fermentation Gas formation –At low pH (< 6), many enteric bacteria produce formate-hydrogen lyase –HCOOH -> H 2 + CO 2 –H 2 is major gas detected by Durham tubes; CO 2 is also detected when produced rapidly; when produced slowly it can dissolve (e.g., in the gut)

9. Other Reductions in Mixed Acid Fermentation Reductive carboxylation to succinate Acetoin (butane diol) fermentation Overview: –Lactate (minor product, as in homolactic) –Formate or H 2 + CO 2 (major product) –Acetate (important product, but must be balanced by equimolar amounts of ethanol, succinate, or butane diol) –Yields an extra ATP for each acetate formed

10. Acetoin Fermentation Part of mixed acid fermentation; dominant fermentation by some (e.g., Enterobacter) Also called butylene glycol or butane diol fermentation Pyruvate + NADH -> *aldehyde + HCOOH + NAD + *aldehyde + pyruvate -> acetolactate -> CO 2 + acetoin (2-keto-3-hydroxy-butane) Acetoin + NADH -> 2,3-butanediol + NAD +

11. Other Fermentation Products Reductive pathways to balance phosphoroclastic reaction –Propionate fermentation –Butyrate fermentation