Protein Biochemistry 2 Flashcards Preview

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Flashcards in Protein Biochemistry 2 Deck (19):
1

The relative directionality of the reactions catalyzed by AST and ALT is determined by ____________.

the concentrations of the reactants

2

Because ___________ is toxic, glutamine is used to transport it from the tissues to the liver.

ammonia

3

The enzyme _____________ is located in peripheral tissues.

glutamine synthetase

4

After glutamine gets to the liver, what happens?

Glutaminase breaks off one NH3 which goes into the production of urea.

5

Two things happen in the kidneys regarding urea: _____________.

ammonia is removed from glutamine and urea is disposed

6

What enzyme in the urea cycle is an anti-cancer drug?

Asparaginase (which deprives cells of asparagine)

7

What enzyme is defective in someone with maple-syrup urine disease?

Branched-chain alpha-keto-acid dehydrogenase

8

Thyroxin is made from ______________.

tyrosine

9

The active form of thyroxin is cleaved be which enzyme?

Deiodinase (which activates T3 from T4)

10

Trace the urea cycle.

NH4 + HCO3
(Mitochondrial carbamoyl phosphate synthetase) ***Rate-limiting; uses ATP***
Carbamoyl phosphate
(Mitochondrial ornithine transcarbamoylase) **Ornithine enters***
Citrulline
(Cytosolic arginosuccinate synthetase) ***Aspartate enters; requires ATP***
Arginosuccinate
(Cytosolic arginosuccinate lyase)
Arginine and fumarate

Fumarate
(Fumarase)
Malate
(Malate dehydrogenase)
Oxaloacetate
(AST)
Aspartate

Arginine
(Arginase)
Urea and Ornithine

11

_____________ is an allosteric activator of carbamoyl phosphate synthetase.

N-acetylglutamate

12

Why do muscles use ALT instead of AST?

Because muscle accumulates pyruvate, which can be shuttled into alanine

13

Describe how ALT and AST "feed" the urea cycle.

ALT produces glutamate, which can release an NH4+ molecule (that enters the urea cycle) by glutamate dehydrogenase. AST can produce aspartate (when the concentration is low) which enters the urea cycle.

14

What protein helps transport urea-cycle reactants to their necessary locations?

ORNT1, which moves citrulline out of the mitochondria and ornithine in.

15

Glutamine transport in the brain is necessary because _______________.

glutamate cannot cross the BBB

16

Glutamate dehydrogenase goes both ways and thus serves as a control point for protein catabolism. What things allosterically stimulate the breakdown of glutamate?

All things that signal low-energy states: ADP, GDP

17

__________ degrades arginine to citrulline and a neurotransmitter.

NO synthase

18

Ornithine and creatine phosphate (a source of energy for muscle) are synthesized from what two reactants?

Arginine and glycine

19

What protein transports T4 and T3 out of cells?

Thyroxin binding globulin

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