Microbio Lecture 27 terms - Anabolic Reactions

general characteristics of biosynthetic (anabolic) reactions

* require ATP as a form of energy
* require reducing power in the form of NADH/NADPH
* reactions are often reversible
* many anabolic reactions are highly conserved

how heterotrophs perform carbon assimilation

get C for anabolic reactions from catabolism of organic molecules

how autotrophs perform carbon assimilation

get C for anabolic reactions from CO2 fixation

what inorganic N assimilates nitrogen into

NH4+, NO3-

what organic N assimilates nitrogen into

protein

what atmospheric N assimilates nitrogen into

N2 fixation

autotrophic pathway

autotrophs get C from CO2 in the air

* calvin cycle (most aerobic and oxygenic autotrophs)
* reverse citric acid cycle (most anaerobic autotrophs)
* reductive acetyl-coenzyme A pathway (anaerobes that metabolize C1 compounds)

the calvin cycle

* fixes CO2 into cellular material for autotrophic growth
* carried out by most photolithoautotrophs and chemolithoautotrophs
* 3 ATP + 2 NADH per CO2 reduced
* 6 molecules of CO2 are required to make 1 molecule of glucose

key enzyme of the calvin cycle

RuBisCO

RuBisCO characteristics

* tolerant to O2
* slow reaction rate
* single most abundant enzyme on earth

carboxysome definition

protein structure used to enhance RuBisCO efficiency by increasing CO2 and decreasing O2

reverse citric acid cycle

* uses ATP and NADH/NADPH to run the citric acid cycle and glycolysis backward
* most enzymes are reversible but 3 are replaced
* requires Ferredoxin

ferredoxin

intolerant to O2

reverse citric acid cycle → net reaction

3 CO2 + 12 H + 5 ATP → C3H6O3PO32- + 3H2O

reductive acetyl-CoA pathway

* used by strict anaerobes that are able to metabolize C1 compounds
* requires the least energy
* was likely present in the first cells

key enzyme of reductive acetyl-CoA pathway

carbon monoxide dehydrogenase

ATP produced by the calvin cycle

3 ATP per CO2

ATP produced by the reverse citric acid cycle

1\.66 ATP per CO2

ATP produced by the reductive acetyl-CoA pathway

1\.33 ATP per CO2

gluconeogenesis

energy used to C2, C3, C4, C5 compounds → citric acid cycle → oxaloacetate → phosphoenolpyruvate + CO2 → reversal of glycolysis → glucose-6-P

nitrogen fixation → key enzyme

nitrogenase

nitrogenase characteristics

* requires lots of energy
* inhibited by O2
* under tight regulation (low O2, low NH4+)

nitrogenase reaction

N2 + 16 ATP + 8e → 2NH3 + H2 + 16 ADP + 16P

nitrogen uptake

* nearly all microorganisms can assimilate ammonia/ammonium
* NH3 incorporated by glutamate dehydrogenase or glutamine synthetase

biosynthesis of amino acids

* carbon skeleton comes from glycolysis or citric acid cycle
* amino group transferred rom glutamate or aspartate

which essential amino acid can humans not synthesize (9)

1. valine
2. leucine
3. isoleucine
4. phenylalanine
5. tryptophan
6. lysine
7. histidine
8. methionine
9. threonine