Lightbody Lecture 17 Flashcards Preview

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Flashcards in Lightbody Lecture 17 Deck (33):
1

AAs

dietary, hydrol tissue prots, or de novo synth; const AA pool of 30g; not stored, but E source when prot catab in starvation; constant need for dietary AAs b/c 25% of AAs metab'd or serve as precursors for other cmpds; prots synth and degrad const (300-400g/d); 11 are nonessential

2

AAs as precursors to...

prots, purines, primidine, HA, nicotinamide, AA Gly + acetate; nts; hormones; Glu, Asp, Gly are all nts by selves

3

Glu and Gln synth

a-KG from TCA w/NH4+--> Glu w/NH4+ -->Gln

4

Asp and Asn synth

OAA (TCA) w/ NH4+ --> Asp w/NH4+ --> Asn

5

Ser and Gly synth

3P glycerate (glycol) w/NH4+ --> Ser w/release of MeTHF --> Gly

6

Ser and Cys synth

3P glycerate (glycol) w/NH4+ --> Ser w/Met, supplies sulfur --> Cys

7

Gly synth

NH4+ + HCO3- w/methylene THF --> Gly

8

Ala synth

pyruvate (glyc) w/ NH4+ --> Ala

9

Pro synth

Glu --> glutamate semialdehyde --> Pro

10

Arg synth

NH3 + CO2 + ATP --> carbamoyl P --> urea cycle --> Arg (intermed in urea cycle, used up there, so semi-essential in adults, completely essential in kids)

11

Tyr synth

Phe (essential) --> Tyr

12

AA catabolism

presence of N in a-amino gp of AA prevents catabolism; dispose of a-amino gp thru transamination, deamination

13

transamination rxns

remove a-amino gp in all AAs except Ser, Thr, Pro (STP); 1st step in catab of AAs; remove amino gp by funneling to a-KG to give Glu and form new a keto acid; all aminotransferases req pyridoxal phosphate (vit B6) - reversible (catab or ana) and spec for one amino gp donor; PLP forms Schiff base w/amino gp of Lys

14

deamination rxns

remove a-amino gp thru oxidative (Glu dehydrog) or hydrolytic (Ser and Thr dehydratase)

15

Ala aminotransferase (ALT/SPGT)

high [] in liver, smaller in <3 and musc; in musc, transfers amino gps from Glu to pyruvate to form Ala, which transports them to the liver; screens liver problems like hepatitis, mononucleosis, cirrhosis, drug tox like excess acetaminophen; ALt levels inc 20-50x in plasma when liver dmg

16

Asp aminotransferase (AST/SGOT)

main fxn is to transfer amino gp from Glu to OAA-->Asp, which enters urea cycle (liver, heart, musc, kidney, brain)

17

oxidative deamination

to Glu; results in liber of amino gp as free NH3; Glu acts as sink for amino gps of AAs thru transamin; amino gp converted to NH4+ by Glu dehydrogenase, regenerating a-KG to accept another amino gp; Glu transported from cyto to mito matrix (where this takes place)

18

Glu dehydrogenase

converts amino gp of Glu to NH4+; also helps to release urea; reversible rxn dep on [] of Glu, aKG, and NH3; + by ADP, - by ATP

19

Thr, Ser, Pro do NOT undergo transamination

Thr-->Gly + aCoA; Ser-->pyruvate + NH4+ +H2O; Pro-->Glu; a-amino of Lys undergoes transam, but other amino gp does not

20

urea cycle

removes toxic ammonia, allowing AAs to be used as E; 90% of all N is removed via urea cycle; liver is major site (only tissue cont all 5 enz); other tisues have some enz's, but only to make Arg and NO

21

carbamoyl phosphate synthetase I (CPS I)

NH3 enters cycle as carbamoyl P in liver mito; NAG activates CPSI - required!;

22

NAG

synth fr aCoA and Glu (N-acetylglutamine synthase) and + by Arg; as Arg levels inc, NAG inc and CPS I inc too

23

CPS II

in cyto, req for pyrimidine biosynth; blocked OTCase results in excess of carbamoyl P, leaving mito and flooding pyrimidine path-->high conc of orotic acid in urine

24

Ns in urea come from...

L-Arg

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argininosuccinate synthase

L-Asp to argininosuccinate; req ATP

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rel b/w TCA and urea cycle

argininosuccinate --> fumarate in cytosol, which becomes malate (which forms OAA) and enters mito matrix

27

urea cycle disorders

1/30,000 live births; usu auto recessive, OTC X-linked; heteros asymp; less severe (partial deficiencies)-->fewer side effects, manifested in later childhood/adulthood

28

severe illness--first week of UCD

usu normal first 24h; symps of hyperammonia in 1-3d; include feeding intolerance, vomit, lethargy, irritability, resp distress (hypervent), seizures, coma; 75% retardation, seizures, visual deficits, prot intolerance

29

type I hyperammonia

CPSI deficiency; NH4 and GLN inc'd (defect in NAG synthase has same effect); visual deficits bad b/c high NH4; b/w carb P materials and carb P

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type II hyperammonia

OTC, X-linked, most common, high pyrimidine, metabolite (orotic acid); b/w carb phosphate/L ornithine and citrulline

31

citrullinuria

arginosuccinate synthase leads to this; citrulline inc; b/w L-citrulline and L-argininosuccinate

32

arginiosuccinic acidemia

b/w L-argininosuccinate and lyase/fumarate (no argininosuccinate breakdown)

33

arginase deficiency

b/w L-Arg and L-ornithine; no urea