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68 Cards in this Set

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Zero Nitrogen Balance
Nitrogen intake=excretion

In mature healthy person anabolism=catabolism and N balance =0
Positive Nitrogen Blaance
Nitrogen intake is greater than Nitrogen excretion

This occurs in growing animal, pregnancy, and recovery from starvation
Negative Nitrogen Balance
Catabolism is greater than anabolism

this occurs in starving animal, acute injury, senescence, and aa defiency
Essential amino acids
histidine
isoleucine
leucine
lysine
methionine
phenylanine
threonine
tryptophan
valine
Why is methionine an essential aa if we have the enzymes to make it?
bc we cant make it at an effient rate
describe protein degradation in the stomach
when pH is less that 5.0
pepsinogen --> pepsin

pepsin hydrolyzes proteins to peptides at points involving aromatic amino acids, leucine, and acidic amino acids
Descibe protein degradation in the intestine
trypsinogen uses enteropeptidase to become trypsin. trypsin then activates more trypsinogen to bcom trypsin, chymotrypsinogen to become chymotrypsin, procarboxypeptidases to become carboxypeptidases, and proelastase to become elastase.
Where are the inactive zymogens secreted from?
the pancrease, they dont become active until they get to SI
What happens once trypsin is activated?
All other zymogens become activated
what makes enteropedptidase that causes activation of trypsinogen?
make by intestinal cells so zymogens cannot be active until in SI
where does trypsin cleave?
after Arg or Lys
Where does chymotrypsin cleave?
after tyr, phe, or trp.
Basically after aromatic rings
Where does elastase cleave?
very small aa. Gly, Ala
Where does carboxypeptidase B cleave?
Must be the last aa of the chain and must be Arg or Lys. So it cleave right in front of the aa to cleave it off peptide
endopeptidase
cleaves w/i the polpeptide chain. Exampes trypsin, chymotrypsin, elastase
exopeptidases
only cleaves off last aa.
example is carboxypeptidase B
why are proteases on the intestinal lining?
bc if not all are free aa and some are some peptides, aminopeptidase and carboxypeptidase cleave the pp to be absorbed
most common disease of aa transport
cystinuria. the gene that encodes for aa transport in the intestinal cells is mutated
cystinuria
defect in the reabsorbtion of dbasic aa(where COOH is protonated) so aa like cystine, ornithine, arginine, and lysine cant be reabsorbed in kidney and intestine. result is kidney stone from poorly soluble cystine.
cystinuria treatment
increase fluit intake and Oral intake of potassium citrate to increase urine pH to 7.5
dibasic aa difiently absorbed in cystinuria
lysine
arginine
ornithine
cystine
in the breakdown of aa what is the first task the cell must accomplish?
remove the alpha amino group
two major mechanisms of nitrogen removal from aa.
1. transamination

2. oxidative deamination
transamination
start out with an aa and alpha ketoglutarate. Use PLP and amino transferase to move Nitrogen of aa to alpha ketoglutarate. so end up with Glutamate and an alpha keto acid
What is PLP?
an intermediate carrier for the amino group. the important reactive group on PLP is the aldehyde bc that is where the amino group binds to be transferred.

The nitrogen group binds the aldehyde of PLP so it becomes PMP and PMP transfers the N group to alpha ketogluterate
How can the aa Ala make the Krebs intermediate pyruvate?
by using alanine aminotransferase and PLP, Nitrogen of Ala is move to alpha ketogluterate. End up with Glutamate and pyruvate
How can the aa aspartate bcome the krebs intermediate oxaloacetate?
Using aspartate aminotransferase and PLP, aspartate gives its nitrogen group it alpha ketogluterate so end up with glutamate and oxaloacetate
What is oxidative deamination?
since all the aa N groups go to glutamate, this is way to get rid of glutamate. If ADP or GDP is hi activates glutamate dehydrogenase this causes glutamate to become alpha ketoglutarate + NH4.

NAD becomes NADH in this rxn
When is oxidative deamination inhibited?
with high ATP or GTP because Krebs does not need to occur so dont need alpha ketoglutarate.

Oxidative deamination is activated by hi ADP or GDP
Problem with oxidative deamination
build up of free NH4, which is very toxic so must go through urea cycle
Why is NH4 Toxic?
Bc NH4 + alpha ketogutarate
-> Gultamate + NH4 -> glutamine

So with too much NH4, alpha ketoglutarate and glutamate decrease. so cant go through krebs to make ATP and cant make NT
Where is Urea Produced?
In liver
Urea Cycle
1.CO2 + NH4 bcome carbonyl phosphate with enzyme carbomoyl phoshate synthtase

2. Ornithine becomes Citruline with enzyme ornitine transcarbomolase. at this point the P from carbomoy phosphate leaves

3. Cituline moves to cytosol and becomes argininocuccinate with argininosuccinate synthetase. Aspartate and ATP bcome AMP and PP.

4.Arginosuccinate uses argininosuccinase lyase to become argine and Fumarate is released

5. Argine uses arginase to become ornithine and urea is releases in cytosol
rate limiting step of urea cycle
CO2 + NH4 uses carbamoyl phosphate synthetase to become carbamoyl phosphate.
What regulate Urea Cycle?
When arginine is hi it activates N acetylglutamate synthase to make N aceylglutamate. N acetylglutamate activates Carbomoyl Phospate Synthetase I.
Where do the N atoms in urea orginate from?
glutamate from oxidative deaminateion
Treatment of hyperammonemia
Low protien diet and/or alternate pathways fro nitrogen excretion.

Take sodium benzoate to conjugate with glycine to form hippurate to pee out

Take phenylbuyrate which is converted to phenylacetate which becomes conjugated with glutamine to form phenylacetylglutamine to pee out
2 group of aa
depends on products of catabolism

1. ketogenic aa

2. glucogenic aa
Ketogenic aa
degraded to acetyl CoA or acetoacetyl CoA

they can produc ketone bodies
Glucogenic aa
degraded to pyruvate, alpha ketoglutarate, succinyl CoA, fumarate, or oxaloacetate

their C skeleton can be used for gluconeogenisis
Ketogenic aa
Leucine
Lysine
Glucogenic and Ketogenic aa
Isoleucine
Phenylalanine
Tryrosin
Tryptophan
Threonine
two genetic defects in aa catabolism
1. PKU
2. Maple syrup urine disease
PKU
defect in catabolism of phe
Maple syrup urine disese
defect in catabolism of ile, leu, and val (Branched chain aa)
the one exception where transamination is not the first step of catabolism
Phe
normal catabolic steps of Phe
1. hydroxylation to form tyrosine catalyzed by phenylaline hydroxlase

2. transamination of tyrosine

3. catabolism of the alpha keto acid of tyrosine (Fumerate and Acetyl Co A)
What is need to convert Phe to Tyr
BH4 and pheylaline hydroxlase
What regenerated BH2 to BH4 after phe is converted to tyr?
dihydrobiopterin reductase w/ NADH as reducing agent
PKU affected gene
phyalalinine hydroxlase (99%)

Dihydorbiopterin reductase 1%
symptoms of PKU
mental retardation, CNS damage, and hypopigmentation
metabolic consequences of patients with PKU
Phe can undergo transamination and make phenylpyruvate, phenylpyruvate then becomes phenyllactate and phenylacetate

Since Phe cant be converted to Tyr, Tyr is low so tyrosine becomes an essential aa. with lo tyrosine, decrease in protein, melanin, catecholamine, and fumerate
Normal catabolism of branched aa (isoleucine, leucine, and valine)
1. transamination

2. alpha keto acid is decarboxylated to acyl Co A this rxn is catalyzed by branched chain alpha ketoacid dehydrogenase
Affected gene of MSUD
genes that encode for branched chain alpha keto acid dehdrogenase complex (BCKAD) has 3 catalytic subunits and two regulatory subunits
five molecules that are precursors to the nonessential aa
1. a ketoglutarate family
(makes glutamate to
glutamine)

2. oxaloacetate family
(makes aspartate)

3. pyruvate family
(makes alanine)

4. 3 phosphoglycerate family
(makes serine, and serine
plus met is cysteine)

5. Tyrosine Synthesis
from phe
synthesis of glutamate
1. reductive amination
a ketogluterate + NH4 -> glutamate

catalyzed by glutamate dehydrogenase NADH ->NAD

2. by transamination. aa becomes a ketoacid and akg become glutamate
sythesis of glutamine from glutamate
glutamate + NH4 -> glutamine

rxn catalyzed using glutamine synthetase and ATP
How to get to glutamate from glutamine
use glutaminase
How is alanine made?
transamination

pyruvate + glutamate -->
alanine + aKG

rxn catalyzed by aminotransferase
how is aspartate made?
oxaloacetate + glutamate -->
aspartate + aKG

catalyzed by aminotransferase
important structural components of tetrahydrofolate (FH4)
6 methylpterin
p aminobenzoate
glutamate

carries 1 C units
important structural componnets of S adenosylmethionine
methioine
adenosine

transfer group of CH4 so methylates stuff
Explain role oftetrahydrofolate is synthesis of glycine
serine + FH4 -> glycine + N5,N10 methylene tetrahdrofolte

catalyzed by serine hdroxymethyl transferase

the FH1 accepts one of serines carbon units
Methyl transfer cycle that utilizes S adenosylmethionine
adoMet ->
s adenosylhomocysteine bc lost methyl group
this is catalyzed by methyltransferases

the S adenosylhomocysteine is hydrolzed to homocysteine and the adenosine is lost. The homocystein can then make methionine with methionine synthase. the methionine can cycle back and become AdoMet by adding ATP and methionine adenosyl transferase
NT synthesis from tyrosine
Tyrosine used tyrosine hydroxlase and BH4 to become Dopa.

Dopa uses PLP and aromatic aa decarboxylase to become dopamine.

dopamine uses dopamine hydroxlase to become norepi

Norepi uses pheylethanolamine N methyltransferase and AdoMet to become epinephrine
Cofactor required fro amino transferase
PLP
NT syntheisis from tryptophan
tryptophan uses tryptophan hydroxylase and BH4 to become S Hydroxytryptophan

S hydroxytryptophan uses aromatic aa decarboxylase and PLP to become serotonin
NT syntheisis from glutamate
glutamate uses glutamate decarboylase and PLP to bcome GABA