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Catabolism: glycolysis & fermentation

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Last revised: Wednesday, February 16, 2000
Ch. 9 (p. 164-168; 174-176) in Prescott et al, Microbiology, 4th Ed.
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 2000. Thomas M. Terry

Breakdown of glucose to pyruvate

1. Embden-Meyerhof (glycolytic) pathway (see handout)

2. Entner-Doudoroff pathway (see handout)

Problem: what do with electrons removed by oxidation reactions?

The critical role of NAD and other temporary electron carriers

NADH (and NADPH) are present in very small amounts. Unless quickly oxidized back to NAD+ (or NADP+), will stop all further oxidation reactions that need these as coenzymes.

Must find some terminal electron acceptor to get rid of electrons ---> waste products to be excreted from cell. What are options?

Solution 1: Fermentation

Lactic acid fermentation

Alcoholic fermentation (2 steps)

Note: WWI -- German biochemist Neuberg solved critical problem of glycerol shortage caused by Allied blockade, needed for explosives.

Add sodium bisulfite to fermenting yeast; adds to acetaldehyde, blocks its use as electron acceptor. Yeasts adapt, use DHAP as electron acceptor, produce glycerol-3-phosphate, then glycerol as waste product.

Formic acid and mixed acid fermentations

useful in identification: 2 common variants
  1. Mixed acid fermentation: some bacteria use several pathways, produce ethanol, formic acid, acetic acid, lactic acid, succinic acid, CO2, and H2. Note lots of acid, lower pH than many other fermentations.

    Note: ATP yield via mixed acid is ~2.5 ATP/glucose, a bit higher than straight lactic acid fermentation

  2. Butanediol fermentation: butanediol produced, also much more CO2, and H2

Why not get rid of hydrogen directly as H2 gas?

Roles of fermentation in nature

What substances can be fermented?

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