01:694:301 Lecture Notes - Lecture 24: Nitrogen Fixation, Pteridine, Nitrogen Balance

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Chapter 24‘Biosynthesis of Amino Acid’
The pathways of biosynthesis are ancient (LUCA);
o Many of the intermediates in energy transduction pathway play a role in biosynthesis
allowing interplay b/w anabolic and catabolic pathways
! Balance created b/w degradation for energy mobilization and synthesis of starting
material
AA synthesis requires solutions to 3 problems
o Nitrogen is essential part of aa; biological systems need to transform NΞN to useable NH3
! Nitrogen fixation; ATP hydrolysis used to ensure rxn is kinetically possible
o Stereochemical control; the correct isomer needs to be made
o Allosteric enzymes and regulation ensure that sufficient amounts of all 20 aa are
maintained for protein synthesis, etc.
Note that carbon skeleton of aa come from intermediates glycolysis, PPP, CAC
KNOW what essential aa are, and KNOW the list presented (711)
o AA synthesis connected to nutrition due to higher organisms losing ability to synthesize
some aa; thus must obtain from diet
o Essential AA – PVT MATT HILL; nonessential is everything else
o Deficiency of any aa leads to
negative nitrogen balance
(more proteins degraded, more N
excreted)
KNOW that many aa can be formed by simple transamination (Refer Ch. 23)
o Glutamine and glutamate can act as aa nitrogen donors
Be able to identify the various derivatives of THF and be able to complete the THF worksheet
(Fig. 24.10)
o Tetrahydrofolate carrier of activated 1-C units (tweezer); mammals obtain THF from
diets (folic acid); also serves as acceptor of 1-C units in degradative reactions
o THF consists of 3 groups: a substituted pteridine,
p
-aminobenzoate, and chain of 1 or
more glutamate residues
o THF carries 1-C unit at N10 , N5, or both (Table 24.2)
! 1-C unit can exists in 3 oxidation states (fully oxy CO2 is carried by biotin NOT THF)
! 1-C unit is interconvertible N5,N10-
methylene
THF can be reduced to N5-
methyl
THF or
oxidized N5,N10-
methenyl
THF
! C-units can also be isomerized from N5-
formyl
THF " N10-
formyl
THF
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