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biochem exam 3 > CH 22: Catabolism of Nucleic Acids and Nucleotides. Anabolism of Nucleotides > Flashcards

CH 22: Catabolism of Nucleic Acids and Nucleotides. Anabolism of Nucleotides Flashcards

1
Q

Catabolism of nucleic acid

How are nucleic acids degraded to nucleotides?

A

Nucleases

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2
Q

Catabolism of nucleic acid

What are the two types of nucleases?

A

Endonuclease: cuts DNA/RNA at a specific site inside

Exonuclease: cuts 1 nucleotide at a time from either the 5’ or 3’ end

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3
Q

Catabolism of nucleic acid

Why are nucleotides important?

A
  • Precursor for DNA/RNA synthesis
  • essential carriers of chemical energy (like ATP)
  • components of NAD+, FAD, and coenzyme A
  • Form activated intermediates (UDP-glucose and CDP-diacylglycerol)
  • cAMP and cGMP are cellular second messengers
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4
Q

Catabolism of nucleotide

What is the order and enzymes for nucleotide catabilism?

A

Nucleotide (using nucleotidase)
* Nucleoside (using Nucleosidase)
* Bases
* Purine
* Pyrimidine
* Ribose/deoxyribose
* Phosphate

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5
Q

Purine Cataolism

What does purine degrade into?

A

Uric Acid

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6
Q

Purine Cataolism

What is the point of convergence for the metabolism of purine bases?

A

Xanthine

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7
Q

Purine Cataolism

What enzyme converts Xanthine to uric acid?

A

Xanthine oxidase

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8
Q

Purine Cataolism

What is the inhibitor for xanthine oxidase?

A

Allopurinol

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9
Q

Purine Cataolism

What happens if there is excess uric acid being made without inhibition?

A

It will build up them precipitate into joints, causing Gout

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10
Q

Purine Cataolism

How is AMP made into Uric Acid?

A

Removal of amino group first then removal of sugar

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11
Q

Purine Cataolism

How is AMP made into Uric Acid?

A

Removal of sugar first then the removal of the amino group

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12
Q

Purine Cataolism

Why is Inosine still a nucleoside?

A

The sugar hasn’t been removed yet, only the amino group.

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13
Q

Pyrimidine Cataolism

What does Pyrimidine degrade into?

A

CO2, NH3, and B-AA

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14
Q

Pyrimidine Cataolism

What AA do C/U degrade to?

A

B-alanine

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15
Q

Pyrimidine Cataolism

What AA does T degrade to?

A

B-aminoisobutirate

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16
Q

Pyrimidine Cataolism

What does dehydrogenase do?

A

it adds hydrogen to the molecules

17
Q

Pyrimidine Cataolism

What does hydrolase do?

A

breaks the ring then splits the pyrimidine into pieces

18
Q

Anabolism of nucleotides

What are the two pathways that lead to nucleotides?

A

De novo pathway: Assembly of a compound from simpler molecules not salvaged from pre-existing similar molecules. It begins with their metabolic precursors: AAs, ribose-5-phosphate, CO2

salvage pathway: synthesis of nucleotides by recyling the free bases and nucleosides from nucleic acid breakdown

19
Q

Anabolism of nucleotides

What are the benefits of the salvage pathway?

A

Saves fuel and energy

Some tissues/organs (brain and bone marrow) can only use the salvage pathway.

20
Q

De novo biosynthesis of purines

Where does De novo synthesis begin?

A

with a reaction of 5-phosphoribosyl 1-pryophosphate (PRPP) with Gln

21
Q

De novo biosynthesis of purines

What is the first intermediate formed with a full purine ring? What get formed from this intermediate?

A

inosinate (IMP)

AMP and GMP

22
Q

Purine Salvage Pathway

What type of enzyme is used to salvage the pieces into AMP/IMP/GMP?

A

phosphoribosyl transferase (adenine for AMP, hypoxanthine-guanine for IMP/GMP)

IMP’s base is hypoxanthine

23
Q

De novo biosynthesis of pyrimidines

What are pyrimidines formed using?

A

Asp, PRPP, and carbamoyl phosphate

24
Q

De novo biosynthesis of pyrimidines

How does pyrimidine synthesis start?

A

FIrst by making the pyrimidine ring then attaching it to the ribose-5-phosphate

25
Q

De novo biosynthesis of pyrimidines

Out of UTP and CTP, which is formed first?

A

UTP is formed first
CTP is formed by the amination of UTP

26
Q

De novo biosynthesis of pyrimidines

What is the first commited step of the reaction?

A

Asp and N-carbamoylphosphate are catalyzed by aspartate transcarbamoylase (ATCase)

27
Q

De novo biosynthesis of pyrimidines

What is ATCase regulated by?

A

Feedback inhibition: which is inhibited by CTP (final product)

28
Q

Pyrimidine Salvage Pathway

How does the salvage pathway for pyrimidine go?

A

Thymine + deoyribose-1-phosphate <-> thymidine + Pi

Thymidine + ATP <-> TMP + AMP

29
Q

Formation of deoxyribonucleotide

How does deoxyribonucleotides form from their ribonucleoside diphosphate forms (ADP, GDP, CDP, UDP)?

A

Reduction of the sugar moiety to produce dADP, dGDP, dCDP, dUDP by removing the oxygen at the C-2 position

Then further processing to get dATP, dGTP, dCTP, and TTP

TTP is always deoxi so it can be put as with dTTP or TTP

30
Q

Biosynthesis of dTMP

What is the precursor of dTMP and what synthesizes the reaction?

dTMP = thymidylate

A

dUMP (from dUTP by dUTPase)

thymidylate synthase

biochem exam 3 (7 decks)

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