Nucleotide Metabolism

Question 1

*How are ribonucleotides converted into deoxyribonucleotides?

Answer 1

dexyribonucleotides are made from ribonucleoside diphosphates.
The 2’ hydroxyl group of ribose is replaced by hydrogen atom in a reaction catalyzed by ribonucleotide reductase which acts on all four ribonucleotides.
Ribonucloside diphosphate + NADPH + H+ use ribonucloetide reductase to form dexyribonucleoside diphosphate and NADP+ And H2O.

Question 2

*Understand the difference between de novo and salvage pathway of nucleotide biosynthesis.

Answer 2

De novo-purines and pyrimidines are made from scratch. Requires A LOT of ENERGY; need activated ribose, amino acids and CO2. to make nucleotide
Salvage- PREFORMED bases are recovered and attached to an activated ribose; uses LESS energy.
activated ribose (PRPP) and base form nucleotide

Question 3

What is a nucleoside, and a nucleotide?

Answer 3

Nucleoside- base attached to sugar

Nucleotide- base attached to sugar and one or more phosphoryl groups (NUCLEOSIDE + phosphoryl group)

Question 4

What are amino acids precursor to?

Answer 4

amino acids are precursors to proteins and other biochemicals like immune system signals, hormones, membrane lipid, electron carriers, and nucleotide bases.

Question 5

how are pyrimidines synthesized? What forms first?

Answer 5

Pyrimidines synthesized from bicarbonate(react with NH3+ form carbamoyl phosphate) , Aspartate and ammonia, with glutamine serving as nitrogen donor.
The pyrimidine is synthesized first, then attached to activated ribose
purines are built on ribose phoshphate.

Question 6

How are nucleoside monophosphates converted to diphophates?

what about diphosphates to triphosphates?

Answer 6

nucleoside monophosphates are converted into diphosphates by specific nucleoside monophosphate kinaes
ex: UMP kinase convert UMP and ATP to UDP and ADP

Diphosphate kinases have broad specificity, catalyze interconversion of di and triphosphates
XDP and YTP convert to XTP and YDP

Question 7

How are purines synthesized?

Answer 7

Purines are synthesized on ribose molecule in de novo pathway. The initial committed step forms 5-phosphorribibosyl 1 amine from PRPP and glutamine (amine is in Beta configuration)

Question 8

What is regulation of ribo/deoxribonucleotide activity?

Answer 8

high dATP will inhbit ribnucleotide reductase
ATP will activate the enzyme
DGTP will activate ADP, TTP will activate GDP
high levels of TTP will shut of reduction of UDP to dUDP and CDP to dCDP.
ATP will activate CDP and UDP