Week 6 - Chemoorganotrophy and fermentation Flashcards
Chemoorganotrophs
energy, electrons, and carbon all obtained by breaking down organic compounds
Chemoorganotrophs found wherever
there is a supply of organic compouds
tend to predominate wherever
a. there is a supply of organic compounds plus oxygen
b. there is a supply of organic compounds and no light (whether oxygen is present or not)
Examples of chemoorganotroph habitats
• soil (if light tends to be aerobic, in anaerobic is usually also dark)
• ocean sediments
• our bodies
eg on the skin (plenty of organic compounds, oxygen)
in our guts (may be anaerobic, but also dark)
All significant pathogens are
chemoorganotrophs
Glycolysis
the Embden-Meyerhof pathway
Glucose + 2ADP + 2 Pi + 2NAD+
–>
2 pyruvate + 2ATP + 2 NADH + 2H+
Glycolysis is common to
respiratory and fermentative metabolism
Glycolysis overall production
2 ATP and 2 NADH per glucose molecule
Significant further oxidation of pyruvate also requires
an electron acceptor - eg oxygen
• in the absence of an electron acceptor == fermentation
Fermentation is basically a way of
removing excess carbon and electrons in the cell
Because of the small amount of energy released by glycolysis
not all the carbon and electrons can be used for anabolic reactions
Examples of fermentation
lactic fermentation
• Streptococcus
• Lactobacillus
ethanolic fermentation
• yeasts
• some bacteria
Lactic fermentation
pyruvate –> lactate
NADH –> NAD+
Ethanolic fermentation
pyruvate –> acetaldehyde
gives off CO2
acetaldehyde –> ethanol
NADH –> NAD+
Other fermentation pathways lead to production of
Propionic acid
• Propionibacterium
Butanediol
• Enterobacter
Butyric acid etc
• Clostridium
Acetic acid + formic acid + ethanol
• many enteric bacteria
Many of the classic tests for bacteria are based on
fermentation products
Fermentation is NOT THE SAME AS
anaerobic respiration
In aerobic respiration
pyruvate is oxidized further
eg the tricarboxylic acid cycle (aka citric acid or Krebs cycle)
Tricarboxylic acid cycle
aka citric acid or Krebs cycle
pyruvate is oxidized further
Pyruvate + 4NAD+ + FAD
–>
3CO2 + 4NADH + FADH
1 ATP formed
After the tricarboxylic acid cycle
the NADH and FADH are re-oxidized by the respiratory electron transport chain - located in the plasma membranes of aerobically growing bacteria
eg
2 NADH + O2 + 2H+
–>
2NAD+ + 2 H2O
For every NADH oxidized
up to 3 molecules of ATP formed
For every FADH oxidized
up to 2 molecules of ATP formed
For every glucose molecule oxidized
38 molecules of ATP form
2 ATP/glucose from fermentatin
glycolysis makes pyruvate
pyruvate through fermentation OR
pyruvate oxidized futher (aerobic respiration - tricarboxylic acid cycle / Krebs / citric acid cycle)
Examples of chemoorganotrophs
- E. coli
- Pseudomonas sp.
- Streptococcus pyogenes
- Mycobacterium tuberculosis
- Bdellovibrio
E. coli is
a gram negative eubacterium
• motile - flagella enable it to swim toward food sources
• able to live on a range of sugars etc - aerobic metabolism on the presence of oxygen, but switches to fermentation when oxygen is scarce