Protein and Lipid Catabolism

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Fermentation

• Releases energy from organic molecules
• Anaerobic, no Krebs cycle or electron transport
  system
• Uses an organic molecule as final electron
  acceptor
• Produces small amount of ATP quickly
• Recycles NADH to NAD
• Occurs in the cytoplasm

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• Lactate fermentation
• The 2 pyruvate molecules that are formed in
  glycolysis are converted to 2 lactate molecules
• The pyruvate molecules accept the electrons from
  NADH and regenerate NAD
• Some organisms rely exclusively on this metabolic
  pathway
• Ex. Lactobacillus bacteria that can produce
  cheeses, yogurt, and sauerkraut

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• Alcohol fermentation
• Enzymes convert each pyruvate molecule to an
  intermediate form acetaldehyde
• The NADH transfers electrons and hydrogen to
  acetaldehyde to form ethanol (an alcohol)
• Certain species of single-celled fungi called
  yeasts are known for their use of this pathway
• EX. Saccharomyces cerevisiae makes bread dough
  rise and Saccharaomyces llipsoideus ferment wine
  from grapes

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Protein and Lipid Catabolism

• Glucose is the main energy supplying carbohydrate
• Microbes may also oxidize lipids and proteins
• Both proteins and lipids must be broken down into
  their individual components in order to enter
  glycolysis and the Krebs cycle
• Each component is oxidized separately

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Lipid Catabolism

• Lipases break down lipids into fatty acids and
  glycerol.
• Fatty acids are converted into acetyl CoA, which
  enters Krebs cycle
• Glycerol is converted into DHAP, which enters
  glycolysis

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Protein Catabolism

• Proteases (peptidases) break down proteins into
  amino acids
• Amino acids can NOT be catabolized directly, so
  they have to be either
• transaminated
• decarboxylated
• dehydrogenated
• Then they are converted into other substances via
  the Krebs Cycle

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Photosynthesis

• Conversion of light energy into chemical energy
• Essentially the opposite of cellular respiration
• 12H2O 6CO2 light energy ? C6H12O6 6O2
  6H2O
• Synthesis of sugars using carbon atoms is called
  carbon fixation
• Two different pathways are used
• Photophosphorylation the light reaction
• Cyclic electrons are released from and returned
  to chlorophyll
• non-cyclic - electrons released from splitting
  water are transferred to NADP
• Calvin-Benson Cycle the dark reaction

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Metabolic Diversity

• Photoautotrophs
• energy obtained by photophosphorylation
• Inorganic compounds are the carbon source
• Cyanobacteria are oxygenic phototrophs
• Green sulfur and purple sulfur bacteria are
  anoxygenic phototrophs
• Photoheterotrophs
• organic compound is carbon source/e- donor
• light is energy source
• green and purple non-sulfur bacteria

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• Chemoautotrophs
• carbon dioxide is carbon source
• inorganic compounds are energy source
• Nitrosomonas and Nitrobacter use nitrogen
  compounds
• Chemoheterotrophs
• complex organic molecules act as energy and
  carbon sources
• most bacteria, all fungi, protozoa, and animals