Chapter 10 Biosynthesis (anabolism)

Goal: produce monomers of the four biomolecules

Amino Acids (Proteins) Simple Sugars (Polysaccarides)Nucleotides (DNA & RNA) 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

Energy &Reducing Equivalents(ATP & NADH)

Monomer Biosynthesis

Biomolecules

Core Biochemical Pathways:

One Carbon Fixation Pathways

Calvin Cycle

Glycolysis (Embden-Meyerhof pathway)Hexose monophosphate shuntEntner-Doudoroff pathway

TCA (Kreb’s) cycleGlyoxylate cycle

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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 isnot the only option as is the case among the eukaryotes

--- the point of the Calvin cycle is to “fix” carbon, create reducedcarbon compounds that can be used for biosynthesis or stored for laterconversion 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 sitaround 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)

--- some prokaryotes can reduce NO3- or NO2

- to NH4+

Biosynthesis

Purine ring

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 upand utilized from the environment if they are available

With sources of the basic chemical building blocks: C, N, O, S, & P mostbacteria can synthesize all 20 commonly appearing amino acidsthe 5 nucleic acid bases as well as the lipids and simple sugars

--- this broad spectrum synthetic ability is what has freed the morecomplex life forms from much of the biosynthetic loadof maintaining ready sources of monomers of the 4 basicbiomolecule types

Biosynthesis Summary