Exam 3 AA Metabolism I (breakdown) Flashcards
what are the 2 sources for protein degradation?
- cellular proteins
2. dietary proteins (ingest)
once we “steal” the amino group from an aa, what is the fate of that amino group?
go on to the urea cycle of be converted into other aas, nucleotides, and biological amines
what is the fate of the carbon skeleton left behind
carbohydrate and lipid pathways
when we ingest proteins, the low pH of the stomach does what proteins
unfolds proteins and activates pepsin
the small intestine has enteropeptidase that acts how
located in the duodenum and cleaves trypsinogen (zymogen) into active trypsin
the small intestine has aminopeptidases that act how
exopeptidases that chew from N-terminus
small intestine has dipeptidases that act how
break apart dipeptides into individual aas
what can be transported into cells
aas, dipeptides, tripeptides (1-3 aas long)
what are the two intracellular primary structures that degrade proteins
- the proteosome (ubiquitin)
2. the lysosome (autophagy)
what is the “N-end Rule”?
the N-terminal aa identity determines rate of ubiquitination
highly stabilizing residues include
small and non-polar
is ubiquitin reusable?
yes
what happens to ubiquitinated tagged proteins
they are fragmented inside the proteosome
what happens to the peptide fragments
cytosolic proteases (proteolysis) further degrade peptide fragments into individual aas
what can we do with individual aas?
reduce, reuse, and recycle
what is it meant to “reduce” aas?
we are reducing waste in our cell (urea)
what is it meant to “reuse” aas?
once we get to the individual aas stage, these aas are still viable to make new proteins
what is it meant to “recycle” aas?
repurpose the carbon skelelton
what part of “reduce, reuse, recycle” slogan does deamination fall under?
reducing and reusing
what is deamination?
separates (-NH3) from backbone (alpha carbon) and leaves behind carbon skeleton
how can we perform deamination (2)
- aas can be directly deaminated by their respective ammonia lyases (dehydratases)
- 2-enzyme mechanism: an aminotransferase + glutamate dehydrogenase
what is the coenzyme for deamination?
pyridoxal phosphate (PLP)
how do we perform direct deamination?
need an ammonial lyase/dehydratase to remove and add back the H2O to remove (NH4+)
_ is deaminated to pyruvate
serine
threonine is deaminated by
threonine dehydratase (like serine)
histidine is deaminated by
histidase
what is step 1 of the 2-enzyme mechanism of deamination?
use an aminotransferase to make glutamate (Glu, E)(combines a primary/alpha aa with a-ketoglutarate).
step 1: when you combine an a-aa with a-ketoglutarate, what are the products?
a-keto acid and glutamate
step 1: what are the 2 names of the aminotransferases
- Aspartate Aminotransferase (AST) - in cells or Serum Glutamate-Oxaloacetate Transaminase (SGOT) - in serum
- Alanine Aminotransferase (ALT) - in cells or Serum Glutamate-Pyruvate Transamminase (SGPT) - in serum
step 1: what is AST and SGOT function?
catalyzes the interconversion of asparatate and oxaloacetate
step 1: what combination gets you products: glutamate (Glu, E) and oxaloacetate (OAA)
a-ketoglutarate and aspartate (Asp, D)
step 1: what combination gets you products: glutamate (Glu, E) and pyrvuvate
a-ketoglutarate and alanine (Ala, A)
step 1: what is ALT and SGPT function?
catalyze the interconversion of alanine and pyruvate
step 1: ALT and AST tell us in the name
what aa
step 1: SGOT and SGPT tell us in the name
what metabolite
what is step 2 of the 2-enzyme mechanism of deamination?
use glutamate dehydrogenase to release an ammonium ion (hydrolase)
a-aa -> glutamate -> _
NADH + (NH4+)
NAD+ + H20 -> glutamate -> _
a-aa
where is NH4+ converted to urea
liver
what excretes urea
kidneys
t/f: (NH4+) is a toxic byproduct of aa catabolism
true
how do muscle cells get (NH4+) to the liver
via alanine and the action of ALT
how does all other cells, except muscle, get (NH4+) to the liver
via glutamine (Gln, Q)
mechanism behind (NH4+) transport from cells, except muscle, to the liver
Gln-synthetase adds an amine to Glu to make Gln and Glnase in the liver removes an amine from Gln to make Glu
chemical formula of urea?
CO(NH2)2
urea cycle: what is the purpose of carbamoyl phosphate synthetase I (CSPI)
the commited step where CPSI combines CO2 and NH3 to make carbamoyl phosphate using 2 ATP
urea cycle: what is the allosteric activator of CPSI?
NAG (N-acetylglutamate) non-proteinogenic
what are the non-proteinogenic aas of the urea cycle
ornithine and citrulline
urea cycle: ornithine must move into the _ to combine with carbamoyl phosphate
mitochondria to make citrulline
urea cycle: citrulline is exported from the _ to the _
from the mitochondria into the cytoplasm
urea cycle: what aa donates an NH3 at the cost of 2 ATP-equivalents to citrulline
aspartate (Asp, D)
urea cycle: what is created after Asp dontates NH3 to citrulline
the aa acid arginine (Arg, R) is created and the rest of Asp is fumarate that enters the mito to make OAA which uses TCA cycle
urea cycle: OAA to Asp conversion is performed by
AST (regeneration loop)
urea cycle: _ is created when urea is removed from Arg
ornithine via H2O which adds the final O to urea
urea cycle: ornithine enters into the _ and continues the urea cycle…
mitochondria
aas are glucogenic if they:
are degraded into intermediate molecules that can feed through gluconeogenesis to reform glucose ex pyruvate
aas are ketogenic if they:
are degraded into intermediate molecules that can be used to create ketone bodies i.e. acetyl-coA and acetoacetate
aas are both ketogenic and glucogenic if they:
can be degraded to more than one possible molecule
what are the ketogenic only aas?
leucine (Leu, L) and lysine (Lys, K)
what are the both ketogenic and glucogenic aas?
- isoleucine (Ile, I)
- phenylalanine (Phe, F)
- threonine (Thr, T)
- tryptophan (Trp, W)
- tyrosine (Try, Y)
