Topic 16: Nucleotide Catabolism Flashcards Preview

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Flashcards in Topic 16: Nucleotide Catabolism Deck (24)
1

What are the Purines?

Adenine and Guanine

DOUBLE RING Structure

2

What are the Pyrimidines?

Thymine, Cytosine and Uracil

SINGLE RING

3

What is a nucleotide?

Base + Sugar + Phosphate

4

What is a nucleoside?

Base + Sugar

5

Simply stated, how are Pyrimidines broken down?

Eventually catabolized to CO2, H2O, and NH3.

Can potentially be used for energy.

(purines CANNOT be used for energy, waste only)

6

What is significant about Thymine degradation?

It eventually becomes Propionyl CoA --> Succinyl CoA --> GLUCONEOGENIC

Beta-aminoisobutyrate (B-AIB) intermediate before Propionyl CoA

B-AIB can be measured in the blood to indicate CANCER, excessive cell death, follow Chemotherapy

7

What is significant about Cytosine degradation?

1st step deaminated to make URACIL --> eventually becomes --> Acetate --> Acetyl CoA --> NOT GLUCONEOGENIC

Beta-Alanine intermediate before Acetate

Beta-Alanine and B-AIB from Thymine are structurally related to GABA and Glycine, inhibitory neurotransmitters.

8

What is significant about Uracil degradation?

It comes from Cytosine degradation! Makes Acetyl CoA and is NOT GLUCONEOGENIC

9

Simply stated, how are Purines broken down?

They become URIC ACID - cannot be utilized for energy, only waste!

Purine -> Uric Acid -> Renal Filtrate --> Reabsorption --> Liver --> Uric acid becomes ALLANTOIN --> excreted in urine

10

What is the enzyme that breaks Uric Acid into Allantoin?

URICASE

11

What animals excrete Uric Acid in their urine?

Primates, Birds (and Reptiles), Insects and DALMATIONS

12

What animals further breakdown Allantoin for excretion?

Bony fish secrete Allantoic Acid through gills

Amphibians and Cartilaginous Fish secrete Glyoxylate and Urea in Urine

13

What is Step 1 of GMP (purine) breakdown?

GMP Remove the Phosphate with Nucleotidase --> Guanosine

14

What is Step 2 of GMP (purine) breakdown?

Guanosine Remove the Ribose via Purine Nucleotide Phosphorylase --> Guanine

15

What is Step 3 of GMP (purine) breakdown?

Guanine Remove Amino group --> Xanthine

16

How is AMP broken down?

AMP remove Phosphate --> Adenosine remove ribose --> Adenine remove amino group --> Hypoxanthine via Xanthine Oxidase --> Xanthine

AMP can be converted by Adenosine Deaminase to IMP pathway at any time by removing amino group. All roads lead to Xanthine.

17

What happens to Xanthine once this step has been reached in purine breakdown?

Xanthine Oxidase converts it to URIC ACID

18

What is Allopurinol?

A drug that inhibits XANTHINE OXIDASE, inhibiting Xanthine breakdown to URIC ACID.

Useful in treating Gout (humans and birds) and Kidney Stones in Dalmatians

19

What happens in (1) Adenosine Deaminase deficiency?

Bubble Boy Syndrome!! (associated with SCID)

Adenosine accumulation --> Immundeficiency of both B and T cells

Prevents breakdown of Adenosine, buildup controls production of G nucleotide --> backup of purines inhibits both purine and pyrimidine synthesis --> everything's fucked

20

What happens in (2) Purine Nucleoside Phopshorylase deficiency?

SCID - Severe Combined Immunodeficiency

AMP and GMP buildup--> inhibits PRPP synthesis --> all nucleotide synthesis is inhibited --> leads to T-CELL DEFICIENCY

Cannot remove ribose

21

Of the purine breakdown enzyme deficiencies, what happens in (3) Xanthine Oxidase deficiency?

Results in Gout or Urinary Stone formation.

22

Of the purine breakdown enzyme deficiencies, what happens in (4) HGPRTase deficiency?

Lesch-Nyan Syndrome => self-mutilation!

X-linked recessive --> males only typically

23

What is HGPRTase?

Hypoxanthine-Guanine Phosphoribosyltransferase -- salvage pathway enzyme

Takes PRPP and puts sugar and phosphate back onto Purine to make IMP and Pyrophosphate (PPi)

Purine + PRPP via HGPRTase --> IMP + PPi

24

What would a nucleotide rich diet consist of?

Testes and Thymus