Microbial Metabolism Notes

Microbial Metabolism

The most abundant organic compounds in organisms are:

• Protein
• Nucleic Acids
• Carbohydrates
• Lipids

Microbial Metabolism

• Metabolism: the sum of all chemical reactions within a living organism
• There are two phases
• Anabolism: constructive metabolism
• The synthesis reaction
• Catabolism: destructive metabolism
• The decomposition reactions

Enzymes

• Enzymes are biological catalysts and are reusable protein molecules that cause a chemical change while staying unchanged itself

• Substrates: the substance upon which an enzyme acts

Enzyme components

• Apoenzyme: protein portion of an enzyme
• Cofactor: non-protein component of an enzyme
• Example: iron, zinc, magnesium, calcium
• Coenzyme is a cofactor that is an organic molecule
• Example: vitamins
• Holoenzyme: apoenzyme and cofactor

Factors influencing Enzyme Action

• Terminology:
• Optimum: the environmental state where the enzyme functions the most efficiently
• Maximum: the maximum environmental limit in which the enzyme can function
• Minimum: the minimum environmental limit in which the enzyme can function
• Inhibitors:
• Competitive inhibitors
• Competitive inhibitors are agents that fill the active site of an enzyme
• They compete with the substrate
• Non-competitive inhibitors
• These agents do not compete with the substrate for the enzyme’s active site, but rather a different region of the enzyme
• This is known as allosteric inhibition.

Pathways of Energy Production

• Most of a cell’s energy is produced from carbohydrate catabolism
• Glucose is the most commonly used carbohydrate
• To produce energy in the form of ATP from glucose, microbes use two general processes:
• Respiration: glucose is completely broken down
• An ATP generating process in which molecules are broken down and the final electron acceptor is an inorganic molecule
• In aerobic respiration
• The final electron acceptor is oxygen
• Final products: carbon dioxide and water and a high yield of ATP (38 total)
• In anaerobic respiration
• The final electron acceptor: inorganic molecule other than oxygen
• Much smaller yield of ATP
• Fermentation: glucose is partially broken down

• Fermentation does not require oxygen
• final electron acceptor: organic molecule
• Produces only small amounts of ATP, total 2 ATP
• Much of the original glucose energy remains in the chemical bonds of the organic end-products
• Example: ethanol or lactic acid

Classification of Microbes by Modes of Nutrition

• Phototrophs

• Chemotrophs

• Autotrophs
• Photoautotrophs

• Heterotrophs
• Chemoheterotrophs
• Parasitism
• Saprophytism or Saprotrophism

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