LECTURE 30 - AA SYNTHESIS AND BREAKDOWN Flashcards
how does the body avoid NH3 toxicity?
glutamine synthetase incorporates NH3 to glutamate to make glutamine
muscle pyruvate is converted to pyruvate
carbamoyl phosphate synthetase assimilates NH4
two NH3 moieties are incorporated in urea, which is excreted by the kidney
CPS-2 vs CPS-1
compartmentalization ensures that both products are made
how is urea production regulated?
high arginine concentration stimulates urea production
CPS-1 is activated by substrate availability
what are the fates of urea and fumarate?
urea is exported to the kidneys
fumarate goes into the CAC to make NADH
what can the carbon skeleton of an amino acid become?
what are the three pathways for amino acids
- gluconeogenic only:
glutamate
glutamine
histidine
proline
arginie
valine
methionine
aspartate
asparagine
alanine
glycine
cysteine
serine - ketogenic only:
leucine
lysine - keto and gluconeogenic:
tryptophan
phenylalanine
tyrosine
threonine
isoleucine
what do the three types of pathways lead to?
glucogenic only:
pyruvate or CAC intermediate
glucose exported to other tissues
ketogenic only:
make ketone bodies
exported to blood to serve as energy source in brain and heart
serve to produce NADH and FADH2
and both just do both
how are branched chain amino acids degraded?
valine, isoleucine and leucine
not degraded in the liver
degraded by branched chain aminotransferase in muscle, adipose, kidney and brain
this forms alpha keto acids
next, branched chain alpha keto acid dehydrogenase complex (uses CoA-SH, NAD and releases CO2) makes acyl-CoA derivatives
a deficiency in that second enzyme causes maple syrup urine disease
how does branched chain ketoacid dehydrogenase complex work?
works in same way as the PDC
the E2 and the E3 are the same in both enzyme complexes
in abundance of leucine’s keto acid, the complex’s kinase is shut off,
E1 turns on and the enzyme goes on
what are the non essential amino acids
alanine
aspartate
asparagine
glutamine
glutamate
how are those non essential amino acids made from common metabolites?
what are the different things that methionine can do?
one carbon metabolism
methylation of DNA
protein synthesis (the first AA)
synthesis of cysteine
methionine metabolism
what is one carbon metabolism?
reminder: where else is the one carbon pathway used?
used in the liver to make PE–>PC
what can homocysteine be turned into?
uses serine to make cysteine
can also be turned into succinyl-CoA
methionine and homocysteine are glucogenic
what is hyper-homocysteinenia?
elevated homocysteine plasma levels
imbalance between rate of production and breakdown
B12 and folic acid deficiencies
this is the only pathway where B12 is used
mutations in the enzyme that converts homocysteine to cystathionine: cystathionine beta synthase
biotin is also a cofactor
how is cysteine made?
via homocysteine
transsulfuration using PLP
cysteine is conditional essential
what are the cofactors required in methionine metabolism?
- vitamin B6 is required for PLP (#5 and #6)
- vitamin B8 (biotin) (#8)
- vitamin B9 (folic acid) (#4)
- vitamin B12 (#4 and #10)
what does vitamin B12 deficiency lead to?
summary of AA catabolism?
