Protein Biochem

Question 1

Gluconeogenic aa

Answer 1

Can be used in gluconeogenes

Question 2

Ketogenic aa

which two?

Answer 2

LEUCINE and LYSINE

Can be broken down to be used in the TCA cycle (or for ketone synth - Acetyl CoA)

Question 3

Breakdown in gut by …

Answer 3

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)

Question 4

Breakdown in tissues ..

Answer 4

degraded by ubiquination that targets by proteasomes (for endogenous proteins, ATP dependent) or lysosomes (for exogenous proteins, not ATP dependent)

Question 5

Nitrogen (from a.a to urea)

Answer 5

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

Question 6

Sulfur containing a.a.?

Answer 6

Methionine (essential) and cysteine (unessential)
Form disulfide bridges
Cysteine is component of glutathione - important for protection against free radical injury

Question 7

Aromatic a.a. precursors for?

Answer 7

5HT, DA, NE, epi, BH4, melanina, thyroid hormone, niacin

Question 8

a.a. that are both glucogenic AND ketogenic

Answer 8

TIPT!
Tyrosine, Isoleucine, Phenylalanine, Tryptophan
(IsoL and the rings - NT precursors)

Question 9

Post translational mods

Answer 9

Phosphorylation: hydroxyl of serine, threonine, tyrsoine
Hydroxylation: proline and lysine for normal collagen (needs vit C)
Carboxylation: glutamic acid (needs Vit K) - 1972 factors

Question 10

Cofactor for aminotransferases?

Answer 10

PLP, derivative of B6 (temporarily holds amino group when removed from a.a. but before attached to glutamate)

Question 11

Transamination

Answer 11

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

Question 12

ALT generates …

And is found in?

Answer 12

glutamate and pyruvate

LIVER ONLY

Question 13

AST generates …

And ins found in?

Answer 13

oxaloacetate and glutamate (can convert these to asp to enter urea cycle)
LIVER, KIDNEY, HEART, MUSCLE, BRAIN

Question 14

Release of NH3 from glutamate catatlyzed by?

Answer 14

glutamate dehydrogenase (NOT an aminotransferase)

Question 15

Goal of urea cycle?
Why?
Location?
Sources of Nitrogen?
What is recycled?

Answer 15

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

Question 16

4 urea cycle control points

Answer 16

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

Question 17

What carries NH3 from peripheral tissues to urea cycle?

Answer 17

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

Question 18

Glucogenic aa vs Ketogenic aa

Answer 18

Glucogenic aa can make glucose (C in > C out)

Ketogenic can make ketone bodies (2 C in ,2 C out)

Question 19

Thyroxin production

Answer 19

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]

Question 20

Porphyrins are?

Answer 20

Cyclic molecules that bind metals
Heme is one (binds Fe) - produced in liver
So porphyrias are defects in heme synthesis

Question 21

Heme synthesis (problem with ALA synthase leads to?)

Answer 21

sideroblastic anemia

Glucose and heme inhibit ALA synthase

Question 22

Heme degradation produces?

Answer 22

Bilirubin

Question 23

Acute intermittent Porphyria (defect in?)

Answer 23

porphobilinogen deaminase

Question 24

Porphyria Cuneata Tarda (defect in?)

Answer 24

uroprophyrinogen decarboxlyase

Most common porphyria (tea colored urine)

Question 25

Glutathione

Answer 25

tripepetide with cysteine as central a.a.

[cysteine peptides usually extracellular]

Question 26

SAM?

Answer 26

S-adenylmethionine
intermediate in cysteine production
can be converted to SAH (SA-homocysteine) which can make methionine OR cysteine

Question 27

Hyperhomocyteinemia (caused by low what? effect?)

Answer 27

low folate, B6, B12

cyteine becomes essential so you have to treat with B6, B12 and folate

Question 28

Homocysteinuria

Answer 28

Can’t convert homocysteine to cystathionine
Defect in cystathionine beta-synthase
Treat: give B6, B12, folate and restrict methionine intake