Protein Biochem Flashcards
Gluconeogenic aa
Can be used in gluconeogenes
Ketogenic aa
which two?
LEUCINE and LYSINE
Can be broken down to be used in the TCA cycle (or for ketone synth - Acetyl CoA)
Breakdown in gut by …
peptidases break down proteins to aa then absorbed by eneterocytes
Pepsin: hydrolyzes N-terminal of Phe, Tyr, Trp
Trypsin: hydrolyzes C-terminal of Arg, Lys (and activates the other enzymes that do the rest)
Breakdown in tissues ..
degraded by ubiquination that targets by proteasomes (for endogenous proteins, ATP dependent) or lysosomes (for exogenous proteins, not ATP dependent)
Nitrogen (from a.a to urea)
1) a.a. donates NH2 group to alpha-ketoglutarate via aminotransferase. Produces: L glutamate and an alpha-keto acid
2) accepted NH2 released as NH3 and alpha-ketoglutarate regenerated
3) NH3 converted to carbomyl phospate by CPS1
4) N from CP ultimately combines with NH3 from asapartate to make urea (UREA CYCLE)
5) urea leaves body as urine
Sulfur containing a.a.?
Methionine (essential) and cysteine (unessential)
Form disulfide bridges
Cysteine is component of glutathione - important for protection against free radical injury
Aromatic a.a. precursors for?
5HT, DA, NE, epi, BH4, melanina, thyroid hormone, niacin
a.a. that are both glucogenic AND ketogenic
TIPT!
Tyrosine, Isoleucine, Phenylalanine, Tryptophan
(IsoL and the rings - NT precursors)
Post translational mods
Phosphorylation: hydroxyl of serine, threonine, tyrsoine
Hydroxylation: proline and lysine for normal collagen (needs vit C)
Carboxylation: glutamic acid (needs Vit K) - 1972 factors
Cofactor for aminotransferases?
PLP, derivative of B6 (temporarily holds amino group when removed from a.a. but before attached to glutamate)
Transamination
First step in protein catabolism
Transfer of amino group from 1 carbon skel to another
Reversible, direction depends on conc of substrate and product
Catalyzed by aminotransferases (AST & ALT)
Creates Asp and Nh3 for urea cycle
ALT generates …
And is found in?
glutamate and pyruvate
LIVER ONLY
AST generates …
And ins found in?
oxaloacetate and glutamate (can convert these to asp to enter urea cycle)
LIVER, KIDNEY, HEART, MUSCLE, BRAIN
Release of NH3 from glutamate catatlyzed by?
glutamate dehydrogenase (NOT an aminotransferase)
Goal of urea cycle? Why? Location? Sources of Nitrogen? What is recycled?
remove toxic NH3 by forming less toxic N containing urea
BECAUSE body cant store amino acids due to toxicity of NH3
In cytosol and mitochondria
Sources: aspartate and NH4+
Ornithine
4 urea cycle control points
1) direction of transamination (depends on conc)
2) NAGS required to activate CPS1 (IN MT!) to start urea cycle (glutamate is substrate)
3) direction of deamination by Glu dehydrog (depends on conc)
4) ATP and GTP allosteric inhib of Glu dehyrog, ADP and GDP activators
What carries NH3 from peripheral tissues to urea cycle?
Glutamate
(which is also a substrate for NAG, the cofactor for CPS1, so if you have a lot of glutamate, it will drive the urea cycle)
GlutaMINE has TWO spots to carry ammonia so sometimes glutamate is converted to glutamine
Glucogenic aa vs Ketogenic aa
Glucogenic aa can make glucose (C in > C out)
Ketogenic can make ketone bodies (2 C in ,2 C out)
Thyroxin production
T4 is a prohormone that is converted to T3 by deiodinase
T4 (thyroxin) is made from Tyrosine in thyroid
Starts as thyroglobulin (`140 tyr)
Free Iodide oxidized to iodine (I2) by thyroid peroxidase
2-5 try is thryoglobulin are iodinated and cleaved to T4
[TSH stimulates release of T4 and T3 and I- uptake]
Porphyrins are?
Cyclic molecules that bind metals
Heme is one (binds Fe) - produced in liver
So porphyrias are defects in heme synthesis
Heme synthesis (problem with ALA synthase leads to?)
sideroblastic anemia
Glucose and heme inhibit ALA synthase
Heme degradation produces?
Bilirubin
Acute intermittent Porphyria (defect in?)
porphobilinogen deaminase
Porphyria Cuneata Tarda (defect in?)
uroprophyrinogen decarboxlyase
Most common porphyria (tea colored urine)
