Topic 3-L6 - Biosynthesis Flashcards
Nitrogen fixation
Some organisms (rare, bact. and archaea) produce nitrogenase –enzyme that converts N2 to NH3
Bact. And archaea that can do nitrogen fixation are known as
“diazotrophs”. E.g. - cyanobacteria,
rhizobia, some archaea methanotrophs
Why convert NH2 to NH3 during nitrogen fixation
NH3 is a much more metabolically useful form of nitrogen – can be used by cells as a nitrogen source for building nitrogen containing molecules (e.g., nucleic acids, protein, etc)
Nitrogenase is comprised of two
proteins
dinitrogenase & dinitrogenase reductase - use Fe/Mo
cofactors
In nitrogen fixation, Electrons come from
Fe/S proteins such as flavodoxin – transferred to dinitrogen reductase – to dinitrogenase – to N2.
Activation/reduction of triple bond
very energetically demanding –requires adding
6 electrons (8 electrons consumed) - 2 ATP per electron…16 ATP per 2 NH3 produced!
Building the cell’s molecules: gluconeogenesis
Producing glucose (for carbon/energy storage or as a precursor for biosynthesis) done using gluconeogenesis
gluconeogenesis is basically the reversal of
Glycolysis
In gluconeogenesis, what’s produced
Glucose-6-P produced which is the activated to produce other mol.
Producing sugar-containing molecules
By activating glucose
Glucose can be “activated” by the
addition of
nucleotide diphosphates
such as ADP-glucose, UDP-glucose
(using ATP, UTP)
Activated form used to produce
polysaccharides for:
- LPS (Gram negative outermembrane)
- NAM/NAG (peptidoglycan)
- Storage molecules like glycogen/starch – later used for carbon/ energy
Amino acids needed to produce
proteins and more (e.g. peptidoglycan)
In the formation of amino acids, Carbon skeletons come mainly from
intermediates of the citric acid cycle,
glycolysis
inorganic nitrogen sources such as NH3 used to build
nitrogen-containing molecules (e.g. amino acids)
What are key enzymes for using NH3 to build nitrogen containing mol.?
Glutamate dehydrogenase and glutamine synthase
(efficiently incorporate NH 3
even at low levels)
Glutamine/glutamate then act as
nitrogen donors to produce many
other key nitrogen-containing molecules in the cell
NH3 + ⍺-ketoglutarate (CAC)
Used to make
glutamine (AA)
Second amine added to make
glutamate (AA). Glutamine /
glutamate are key N sources.
When making lipids, Fatty acids built 2 carbons at a time by using adding
malonyl-CoA(3 carbons) to growing
chain – CO2 released as biproduct
ACP =
involved in the chemistry
acyl carrier protein “holder” of
substrates for fatty acid synthesis
Malonyl-ACP made from…
malonyl-CoA made from…
malonyl-CoA
acetyl-CoA (CAC)
Fatty acids can be added to glycerol backbone to produce
membrane phospholipids
When building nucleotides, Basic building blocks:
pentoses (5C sugar, ribose) & nucleobases
Pentose phosphate pathway (parallel to glycolysis) generates
ribose-5-phosphate from glucose-6-phosphate.
Pentode phosphate pathway also generates
NADPH and a range of other important carbon skeletons
Purines
(A/G)
pyrimidines
(U/T/C)
Purines and pyrimidines produced together?
No seperate pathways
Key intermediates IMP (purines) and orotate (pyrimidines) used as
common intermediates to produce final products for nucleotides
In the formation of nucleotides, Ribonucleotides produced
(RNA) first.
Once RNA is formed, Ribonucleotide reductase then converts
ribonucleotides into
deoxyribonucleotides for
DNA synthesis
