Download Metabolism, Glycolysis, & Fermentation

Microbial Metabolism
Nestor T. Hilvano, M.D., M.P.H.
Learning Objectives
You should be able to:
1. Describe the three stages of aerobic glucose
catabolism (glycolysis, the Krebs cycle, and the
electron transport chain).
2. Compare the pentose phosphate pathway and
the Entner-Doudoroff pathway with glycolysis in
terms of energy production and products.
3. Describe fermentation and contrast it with
respiration.
4. Identify useful end-products of fermentation, and
explain how fermentation reactions are used in
the identification of bacteria.
Obtaining Energy
• Autotrophy – self feeding; utilize CO2
1. photoautotrophs
2. chemoautotrophs (oxidize inorganic subst.,
nitrites and sulfides)
• Heterotrophy – other feeding; use organic
molecules
1. photoheterotrophs (chemical energy from
light)
2. chemoheterotrophs (chemical energy from
breaking down organic materials)
Carbohydrate Catabolism
• Polysaccharide hydrolysis to
monosaccharides then to glucose
• Glycolysis
– 2 pyruvic acid, 2 ATP, 2 NADH
(Substrate level phosphorylation)
• Either via
1. Cellular respiration – CO2 and water
waste products); with 38 ATP’s
2. Fermentation – acid; alcohol (organic
waste products); with 2 ATP’s
Alternate Pathways to glycolysis
• Pentose phosphate (phosphorylated 5
Carbon sugar – ribulose, xylulose, ribose)
• Produce precursor metabolites
- used in synthesis of nucleotides, amino
acids, and glucose by photosynthesis
• 1 ATP, 2 NADPH
Alternate Pathways to glycolysis
• Entner-Doudoroff
- used by gm. - Pseudomonas
aeruginosa; gm. + Enterococcus faecalis
• Catabolize glucose to pyruvic acid
• Net 1 ATP, also yield precursor
metabolites and NADPH, not produced by
pentose phosphate pathway
Cellular respiration
• Aerobic respiration – total 38 ATP
• Synthesis of acetyl-CoA – lose a CO2; gain NADH
• Krebs cycle/citric acid cycle/TCA cycle (cytoplasm
in prokaryotes) – net 2 ATP, 6 NADH, 2 FADH2, 4
CO2
• Electron transport chain (in mitochondria)
- passing e- to final e- acceptor (H2O)
- NADH (yield 3 ATP) and FADH2 (yield 2 ATP)
• Summary: glucose + 6 O2 → 6 CO2 + 6 H2O + energy (38
ATP)
• Anaerobic respiration (reduction of sulfate, nitrate,
carbonate, and give off methane)
Fermentation
• Partial oxidation of sugar to release energy
(oxidize NADH to NAD+)
• Summary:
Glucose → 2 Lactic acid + 2 ATP
Glucose → 2 ethanol + 2 CO2 + 2 ATP
• Some useful in health and industry
• Others are harmful
- Clostridium perfringens results to gangrene
- wine spoilage (acetic/lactic acid)
Homework
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Define terms: autotrophy, heterotrophy, aerobic
respiration, anaerobic respiration, Entner-Doudoroff
pathway, and pentose phosphate pathway.
Describe glycolysis, kreb cycle, and electron transport
chain.
What intermediate (chemical) product is needed to
enter through the kreb’s cycle?
In electron transport of oxidative phosphorylation, what
are the electron carriers? What is the final electron
acceptor?
What process is common to both cellular (aerobic)
respiration and fermentation (non-aerobic)?
Describe lactic acid fermentation and ethanol
fermentation.
List 4 useful fermentation products.