AA - Degradation and synthesis 20 Flashcards
Which two aa are nonessential and can be synthesized from essential aa?
cysteine
tyrosine
AA that are glucogenic AND ketogenic
Nonessential:
- tyrosine
Essential:
- Isoleucine
- phenylalanine
- tryptophan
AA that are ketogenic
Essential:
- Leucine
- Lysine
Catabolism of Ketogenic AAs yield . . .
aa whos catabolism yields either:
acetoacetate
or its precursors ( acetyl coA/acetoacetyl coA)
AAs that form oxaloacetate and how
asparagine –> aspartate + NH3 via asparaginase
Aspartate –> oxaloacetate + glutamate via aminotransferase (transamination)
Glutamate can be transaminated or oxidatively deaminated and converted to a-ketoglutarate. Which AAs can form glutamate, and ultimately a-ketoglutarate?
- Glutamine
- Proline
- Arginine
- Histidine
Gln, Pro, Arg, His
Q, P, R, H
pg 262
AA that form Pyruvate
- Alanine
- Cystine
- Glycine
- Serine
- Threonine
Major gluconeogenic AA
ALanine –> pyruvate
- loses its aa by reversible transamination to form pyruvate
AA that form fumarate
Phenylalanine
Tyrosine
(both are glucogenic + ketogenic)
Phe gets converted to Tyr via phenylalanine hydroxylase
Tyr can then form fumarate + acetoacetate
There is a relationship with homocysteine to what types of diseases?
vascular
- elevated lvls promote oxidative damage
- inflammation
- endothelial dysfxn
- occlusive vascular disease
Plasma homocysteine levels are inversely associated with high lvls of what 3 vitamins?
Folate
B6
B12
Pregnant women are given folate to prevent what?
NTD
- Folate is inversely related to homocysteine levels
Low homocysteine levels help prevent NTD
Branched chain aa are unique in that they are metabolized primarily by?
peripheral tissue (muscle) rather than by the liver
- leucine
- isoleucine
- valine
all are essential
Active form of folate and its use
- what does a deficiency in folate result in?
Tetrahydrofolic acid (THF)
- Made from folate + 2 NADPH
- allows one carbon compounds to be recognized and manipulated by biosynthetic compounds.
- Deficiency presents as megaloblastic anemia
Here are 3 AAs, list their corresponding a-keto acids
alanine
aspartate
glutamate
alanine- pyruvate
aspartate - oxaloacetate
glutamate - a-ketoglutarate
PKU
- cause
- characteristics of classic PKU
- tx
caused by a deficiency of phenylalanine hydroxylase (PAH)
(pg 269 cant convert Phe to Tyr)
- accumulation of Phe
- deficiency in Tyr (Tyr bcomes essential acid in PKU)
- Elevated Phe
- urine has a “mousey” odor - CNS sx
- mental retardation, cant walk/talk, seizure, hyperactivity, tremor, microcephaly, failure to grow - Hypopigmentation
- fair hair, light skin, blue eyes
- Hydroxylation of Tyr is first step in forming melanin
Tx: dietary - ingest nec. protein w low Phe levels
- Phe is essential aa - need it in diet
Dihydropteridine reductate deficiency
Dihydropteridine reductase Regenerates BH4 from BH2
- BH4 is needed for Phe hydroxylase, Tyr hydroxylase, Try hydroxylase
- can result in Hyperphenylalaninemia
Maple syrup urine disease (MSUD)
- cause
- characteristics of classic PKU
- tx
partial or complete deficiency in branched chain a-keto acid dehydrogenase
- Leu, Iso, Val cannot be decarboxylated + accumulate in blood
- infants show sx in first few days of life (can be lethal!)
- Feeding problems:
- vomiting, dehydration - Severe met acidosis
- Maple syrup odor to the urine
Tx: synthetic formula that contains limited amts of leu, iso, val. Just sufficient to grow + develop
*note: branched chain aa are imp E source in times of metabolic need, and indiv with MSUD are at risk for decompensation during periods of increased protein catabolism
Albinism
defect in Tyr metabolism –> deficiency in production of melanin
- increased risk of skin cancer
Homocystinuria
- cause
- characteristics of classic PKU
- tx
group of disorders involving defects in metabolism of homocysteine.
- high lvl homocysteine + methionine
- low lvl cysteine
- most common: defect in cystathionine B synthase
(converts homocysteine to cystathionine)
- ectopia lens (displace lens of eye)
- skeletal abnormalities
- thrombi prone
- osteoporosis
- neuro deficits
tx: restriction of methionine intake and supplementation with Vit folate, B6, B12
Clinically imp aa:
Methionine
Arginine
Glutamine
Methionine
- source of methyl groups in met.
- precursor of cysteine
Arginine
- Member of urea cycle
- precursor of NO
Glutamine
- storage and transport form of ammonia
- precursor of purines an pyrimidines
Clinically imp aa: Phe His Tryp Ala
Phe
- precursor to tyrosine
- elevated in PKU
His
- precursor to histamine
- elevated in histidinemia
Tryp
- precursor to serotonin
Ala
- transport form of ammonia from muscle
- key glucogenic aa
