Nucleotides

Question 1

Functions of nucleotides:

Answer 1

Energy currency: ATP, GTP Energy carrier: FADH, NADH
Enzyme cofactors - Acetyl CoA (adenine)
Genetic information - DNA, RNA
Hormonal(first messenger) signaling - cyclic nucleotides (second messenger), GTP in G-coupled receptors
Metabolic intermediates

Question 2

To which of the C-atoms of the sugar is the phosphate/base attached?

Answer 2

Phosphate: 1
Base: 5

Question 3

Purines (P A G) by numbers:

Answer 3

Adenine: 6-amino purine

Guanine: 2-amino 6-keto purine

Question 4

Pyrimidines by numbers:

Answer 4

Cytosine: 2-keto 4-amino pyrimidine

Uracil: 2,4 keto pyrimidine

Thymine: 5-methyl uracil

Question 5

How are phosphates/bases connected to sugars?

Answer 5

Phosphate: Phosphoester bond

Bases: N-glycosidic bond

Question 6

The enzyme used for Thymidine synthesis:

Source of methyl group:

Answer 6

Thymidylate synthase, methyl group from N5 N10 methylene tetrahydrofolate

Question 7

Substrates of Thymidine synthase:

Products of Thymidine synthase:

Answer 7

Substrate: N5 N10 methylene tetrahydrofolate and dUMP

Products: 7,8 Dihydrofolate and dTMP

Question 8

What happens to 7,8 Dihydrofolate?

Answer 8

It is part of the cycle: 7,8 Dihydrofolate reduced to H4 folate -> H4 folate converted back to N5 N10 methylene tetrahydrofolate (CH3 donor for Thymidine syntahse)

Question 9

Enzyme converting 7,8 Dihydroflae in H4 folate:

Answer 9

dihydrofolate reductase
-> competitive inhibitors: Methotrexate, Aminopterin, Trimethoprim

Question 10

How can the formation of Thymine (dTMP) be inhibited?

Answer 10

-Fluorouracil: has Flourid at position 5 instead of -CH3 and blocks the active site of Thymidine synthase

-inhibition of H4 Folate formation (7,8 Dihydrofolate -> H4 folate)
by Methotrexate, Aminopterin, Trimethoprim -> mimicking folate