Biochemistry - Tutorial (Nucleotide metabolism)

The two purine nucleotides found in RNA are:

• formed in a branched pathway from a common intermediate
• formed in a sequential pathway
• derived from exogenous sources
• formed by oxidation of NADH

Uric acid is

• synthesised from xanthine in the presence of O2
• a degraded product of cytidine
• deficient in the condition known as gout
• a competitive inhibitor of xanthine oxidoreductase

Which of the following descriptions regarding nucleotide catabolism is INCORRECT?

• Nucleotidases degrade nucleotides to nucleosides.
• AMP is degraded to the free base hypoxanthine.
• Xanthine is the common product for AMP and GMP catabolism.
• Catabolism of UTP leads to the formation of uric acid.

Which of the following descriptions regarding deoxyribonucleotides is CORRECT?

• They are essential amino acids.
• They are synthesised de novo without PRPP.
• They are synthesised from ribonucleotides by an enzyme system involving thioredoxin.
• They are synthesised by nucleotide kinases.

Nucleotides required for the synthesis of nucleic acids can be obtained from ___________.

• Hydrolysis of peptide bonds.
• de novo pathway only.
• salvage pathway only.
• De novo and salvage pathway.

For de novo synthesis of purine nucleotides, glycine provides __________________.

• one nitrogen atom
• one nitrogen and one carbon atom
• two carbon atoms
• one nitrogen and two carbon atoms

5-Phosphoribosyl-1-pyrophosphate (PRPP) is required for the synthesis of ____________________.

• purine nucleotides only
• pyrimidine nucleotides only
• purine and pyrimidine nucleotides
• None of the above

Inosine monophosphate (IMP) is an intermediate during de novo synthesis of ________________.

• AMP and GMP
• CMP and UMP
• CMP and TMP
• All of the above

Describe TWO (2) differences between purine and pyrimidine synthesis.

Name ONE (1) important compound/molecule in regulating the de novo synthesis of guanosine monophosphate?