Microbiology Module 5

Precursor metabolites generated during central metabolic pathways (both catabolic/anabolic) and during photosynthesis (Calvin Cycle)

Anabolic rxns produce bldng blocks from precursors, consuming large amounts of ATP and NADPH

Synthesis of bldg blocks requires precursor metabolites and other components (N, S, P, Fe)

Bldg blocks are assembled into macromolecules and cell structures

Most common pathway for CO2 fixation. Taking CO2 out of atmosphere and converting it into carbs

Rubisco is the most common enzyme in nature

Rubisco adds CO2 to a 5C cmpd from pentose phosphate cycle

The 6C sugar breaks down into 2 3C molecules (3PG). 3C molecules then reduced using NADPH

Product G3P feeds into glycolysis

1 CO2 incorporated requires 3 ATPs + 2 NADPH

3 other pathways exist for CO2 fixation (Less common)

Although N2 (gas) is vey abundant, few organisms (bacteria and archaea) can use it directly

All sources of N are converted to NH3/NH4+ and are incorporated into cellular components via glu/gln

Useable N source often growth limiting in free-living microbes

Nitrogenase complexes ANAEROBICALLY reduce N2 to NH3 (nitrogen fixing)

N2 + 8H + 16ATP --> 2NH3 + H2 + 16 ADP/Pi

Many N2 fixers are aerobes, so they must develop schemes to protect nitrogenase from O2

Some N2 fixers are free-living. Some form symbiotic relationships w/plants (legumes) before they can fix N2. ALL ARE PROKARYOTES

Source of nitrogen is Nitrate (Plants and bacteria)

Glu provides nitrogen source for amino acids

Gln is major nitrogen provider for other bldg blocks in 9 diff pathways. It is made by very highly regulated gln synthetase.

Transport and reduction of NO3- for use as N source. widespread in microbes, not HUMANS

2 enzymes are used: nitrate reductase and nitrite reductase

Nitrate reductase contains FAD and Mo and uses e- donor NADPH to make nitrite

Nitrite reductase produces NH3 from NO2-

Needed for AAs, vitamins, cofactors, etc.

Many diff. srouces of sulfur all are converted to Cys that serves as donor for biosynthesis

Phosphate is always transported into cells as inorganic phosphate or as part of small organic molecules that are then catabolized

Chemically very stable and there are no redox reactions involving phosphate in cells

High energy phosphate bonds can be formed and are the basis of storage and transfer of cellular energy

Building blocks are assembled into macromolecules via several processes

Including: DNA (Replication), RNA (transcription), Proteins (Translation), Polysaccharides.lipids, etc.