Transcript Use of Reduced Carbon Compounds

Chapter 10 Biosynthesis (anabolism)
Goal: produce monomers of the four biomolecules
Amino Acids (Proteins)
Nucleotides (DNA & RNA)
Simple Sugars (Polysaccarides)
Lipids
Most bacteria synthesize almost all the monomers that they need for
cell growth directly, whereas we are more used to thinking of animals
that get many of their monomers from food.
--- The simplest building blocks for biosynthesis are the one
carbon, oxidized molecules such as CO2 (carbon fixation)
Use of Reduced Carbon Compounds:
Reduced Carbon Compounds
Monomer Biosynthesis
Biomolecules
Energy &
Reducing Equivalents
(ATP & NADH)
catabolism
anabolism
Core Biochemical Pathways:
One Carbon Fixation Pathways
Calvin Cycle
Glycolysis (Embden-Meyerhof pathway)
Hexose monophosphate shunt
Entner-Doudoroff pathway
TCA (Kreb’s) cycle
Glyoxylate cycle
Other Ways to “Fix” Carbon
Green Sulfur Bacteria --- run TCA cycle in reverse
Chloroflexis --- Hydroxypropionate pathway,
transfer malate to other pathways
Acetogenic bacteria --- CO dehydrogenase pathway
(chemoautotrophs) transfers acetate to other
pathways
Methane OR Methanol --- serine/ formaldehyde pathway
modified, reversed TCA cycle
--- ribulose monophosphate/ formaldehyde
pathway, modified Calvin cycle,
Calvin-Benson Cycle (“Dark Reactions” of Photosynthesis)
--- while many autotrophic prokaryotes use the Calvin cycle it is
not the only option as is the case among the eukaryotes
--- the point of the Calvin cycle is to “fix” carbon, create reduced
carbon compounds that can be used for biosynthesis or stored for later
conversion into cellular energy
CO2  CH2OH
--- this process requires tremendous amounts of energy, 3 ATP
and 2 NADPH per CH2OH unit (18 ATP and 12 NADPH per 6 carbon
sugar) however, the energy input is essentially free (sunlight) and most
prokaryotic autotrophs inhabit niches where they can afford to sit
around and wait
Glycolysis (Embden-Meyerhof pathway)
Glucose + 2 ATP + 2 NAD+  2 Pyruvate + 4 ATP + 2 NADH
Produces:
--- net 2 ATP
--- 2 NADH (for electron transport or NAD+ must be
regenerated by fermentation or biosynthesis)
--- several intermediates can be used for biosynthetic
precusors
--- Does NOT produce CO2
Hexose Monophosphate Shunt (HMS)
--- produces NADPH from Glucose
--- end product useful for nucleotide
biosynthesis and the Calvin cycle
Entner-Doudoroff pathway (ED)
--- variation of gylcolysis produces only 1 net ATP
but also 1 NADPH
TCA cycle
--- 3 CO2 produced
--- 3 NADH
--- 1 FADH2
--- 1 ATP
--- multiple precusors
for biosynthesis
Nitrogen Assimilation and Fixation
--- most organisms obtain N from NH4+ (prokaryotic & eukaryotic)
NH4+ + a-ketogluterate  Glutamate + NH4+  Glutamine
(NADPH)
(ATP)
Biosynthesis
Purine ring
--- some prokaryotes can reduce NO3- or NO2- to NH4+
Nitrogen Fixation
--- the ability to reduce atmospheric N2 to NH3
--- requires considerable energy and specialized enzymes
--- a few bacteria possess this ability and are required by Earth’s
more complex life forms as a source of useable nitrogen
Nitrogenase, the central enzyme in nitrogen fixation, is oxidized and
inactivated by O2
Sulfur and Phosphorous Uptake
--- both sulfate (SO4-) and phosphate (PO4-) are easily taken up
and utilized from the environment if they are available
With sources of the basic chemical building blocks: C, N, O, S, & P most
bacteria can synthesize all 20 commonly appearing amino acids
the 5 nucleic acid bases as well as the lipids and simple sugars
--- this broad spectrum synthetic ability is what has freed the more
complex life forms from much of the biosynthetic load
of maintaining ready sources of monomers of the 4 basic
biomolecule types
Biosynthesis
Summary