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NMSK-A II > Biochemistry > Flashcards

Biochemistry Flashcards

1
Q

Explain why purine biosynthesis is inhibited by AMP and by GMP

A

negative feedback

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2
Q

What is the correlation between hyperuricemia and gout?

A

gout only occurs in individuals who are hyperuricemia

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3
Q

What are the crystals made of in gout?

A

monsodium urate

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4
Q

What is considered abnormally high urate levels?

A

6.8 mg/L of urate

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5
Q

What is uric acid an end product of?

A

nucleotide degradation from purines (not pyrimidines)

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6
Q

How is uric acid excreted from the body?

A

urine or feces

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7
Q

What causes hyperuricemia?

A

excessive production or inadequate elimination of uric acid

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8
Q

Where are dietary purines oxidized?

A

liver

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9
Q

Where are de-novo biosythesized purines oxidized?

A

liver

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10
Q

What causes reabsorption of uric acid in the body?

A

urate1 transporter in kidney

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11
Q

What are dietary purine sources?

A

1) red meat
2) seafood
3) beer

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12
Q

What is glutamine-phosphoribosylpyrophosphate aminotransferase?

A

key regulated step in purine biosynthesis; first step which is inhibited by AMP and GMP and stimulated by PRPP

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13
Q

What is PRPP?

A

Purine biosynthesis starting substrate which is the foundation which purines are built

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14
Q

How is PRPP formed?

A

ribose-5-phosphate and PRPP synthetase

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15
Q

What stimulates PRPP formation and what inhibits it?

A

(+) inorganic phosphate

(-) purines

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16
Q

Where does the ribose-5-phosphate come from?

A

pentose phosphate pathway

17
Q

What is the initial intermediate formed during purine biosynthesis?

A 
inosine monophosphate (IMP)
PRPP --> IMP
18
Q

How is inosine monophosphate biosynthesized?

A

oxidized to XMP which is transaminated to GMP

19
Q

What is one word to describe how drugs are excreted and metabolized from the body?

A

oxidation

20
Q

Why is AMP used to make GTP and GMP used to make ATP?

A

balance each other out where the product in high concentration increases the levels of the product in low concentration

21
Q

What are the 3 steps in purine degradation?

A

1) remove phosphates
2) remove ribose
3) oxidize purine base again

22
Q

Which enzyme is targeted in anti-gout therapies?

A

xanthine oxidase

23
Q

What is purine salvage?

A

saves energy by salvaging purine bases by reattaching them to PRPP using HGPRT which hydrolyzes phosphate group of PRPP

24
Q

What is Lesch-Nyhan disease?

A

HPRT is inactivated by x-linked recessive mutations; leads to severe hyperuricemia

25
Q

What is the effect of fructose on

purine metabolism?

A

Dietary fructose gets trapped almost completely in the liver after it gete phosphorylated. This leads to huge increase in monophosphates (GMP, AMP) and results in increased purine metabolism –> gout

26
Q

What is a byproduct of uric acid?

A

allantoin from urate oxidase; way to expel uric acid from body

NMSK-A II (10 decks)

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