BCM. 38 Bacterial Metabolic Diversity

chemoorganoheterotrophs

• Chemo-:

  The energy is derived from chemical reactions, specifically the oxidation of organic molecules. 

• Organo-:

  The "electron donors" that provide the energy are organic compounds like sugars, fats, and proteins. 

• Hetero-:

  The organism gets its carbon from external organic sources, rather than making it from carbon dioxide. 

• examples -

Metabolism in a chemoorganoheterotroph

• the food and nutrients enter catabolism to form three products - Energy (ATP/change in P), reducing power (NAD(P)H), and precursor metabolites

• these three products are then used in biosynthesis resulting in cell growth

Two ways that any living cell can generate utilisable energy

1. substrate level phosphorylation

• e.g. some phosphorylated metabolic intermediate reacts with ADP which forms substrate + ATP

• e.g. PEP + ADP → Pyruvate + ATP (via pyruvate kinase

2. Oxidative/electron transport phosphorylation

• vectoral process which occurs in membranes (cytoplasmic membrane)

• hydrogen donor is oxidised, electrons are passed through the chain and then the hydrogen acceptor is reduced (free energy is released in this process)

• e.g. NADH is oxidised to NAD+ producing H+, H202 is reduced to H20 as the e- acceptor

PMF (Change in P) and ATP - interchangeable energy currencies

Comparison between mitochondrion and E.coli electron transport chain

Anaerobic respiration in E.coli

• alternative electron acceptors

• differences in energy yield with different acceptors

• nitrate reductase and its respiratory chain in E.coli

• using nitrate as the electron acceptor results in the delta E⁰¹ to become shorter (producing less energy) - this becomes even shorter when using fumarate as the electron acceptor

Nitrate reductase and its respiratory chain in E.coli