Nucleic Acid

• What are nucleotides the building blocks of?

  Nucleic acids
• What are the two types of nucleic acids that nucleotides form?

  DNA and RNA
• What is the universal currency of energy in cells?

  Adenosine triphosphate (ATP)
• What role does ATP play in biochemical reactions?

  It drives important biochemical reactions
• What are cyclic AMP (cAMP) and cGMP classified as?

  Intracellular second messengers
• What important coenzymes are nucleotides components of?

  NAD+ and FAD
• What is the structure of purines and pyrimidines?

  • Purines: Two-ring structure (Adenine, Guanine)
  • Pyrimidines: One-ring structure (Cytosine, Uracil, Thymine)
• Which nitrogenous base is present only in RNA?

  Uracil
• Which nitrogenous base is present only in DNA?

  Thymine
• How are nucleosides formed from nitrogenous bases and sugars?

  • Nitrogenous Base + Pentose → Nucleoside
  • Examples:
  • Adenine + Ribose → Adenosine
  • Guanine + Ribose → Guanosine
• How are nucleotides formed from nucleosides?

  • Nucleoside + Phosphate → Nucleotide
  • Examples:
  • Adenosine + Pi → AMP
  • Guanosine + Pi → GMP
• What is the major site of purine biosynthesis?

  The liver
• What does de novo biosynthesis of purine nucleotides begin with?

  Phosphoribosyl pyrophosphate (PRPP)
• How many steps are involved in the biosynthesis of purine nucleotides?

  Ten steps
• What is the committed step in de novo purine biosynthesis?

  The reaction catalyzed by amidotransferase
• What inhibits the amidotransferase reaction in purine biosynthesis?

  AMP and GMP via feedback inhibition
• What are the two main pathways for nucleotide production?

  1. De novo biosynthesis
  2. Salvage reactions
• What do salvage pathways produce nucleotides from?

  Phosphorylation of free bases and nucleosides
• Why are salvage reactions important in certain tissues?

  They operate where de novo pathway is inactive
• What are purines mainly degraded into?

  Uric acid
• What is hyperuricemia?

  Elevated uric acid level in blood
• What is the uric acid level threshold for hyperuricemia in males?

  Greater than 7 mg/dL
• What is the uric acid level threshold for hyperuricemia in females?

  Greater than 6 mg/dL
• What is the basic structure of a nucleotide?

  Nitrogenous base, pentose sugar, phosphate group
• What are the components of a nucleotide?

  • Nitrogenous base (purine or pyrimidine)
  • Pentose sugar (ribose or deoxyribose)
  • Phosphate groups
• What is the source of the pyrimidine ring in biosynthesis?

  Carbamoyl phosphate and aspartate
• What is supplied by PRPP in pyrimidine biosynthesis?

  Ribose
• What is the first enzyme in pyrimidine biosynthesis?

  Carbamoyl phosphate synthase-II (CPS-II)
• Why is CPS-II considered the rate limiting enzyme?

  It controls the speed of pyrimidine synthesis
• What are the final products of pyrimidine degradation?

  β-alanine, β-aminoisobutyrate, NH3 & CO2
• How do pyrimidine catabolites compare to urate in terms of solubility?

  Pyrimidine catabolites are highly soluble
• What might affect de novo biosynthesis of pyrimidines?

  A diet low in aspartate, glycine & glutamine
• Why are aspartate, glycine, and glutamine considered non-essential amino acids?

  They can be converted from other amino acids
• What is required for the reduction of ribonucleotides to deoxyribonucleotides?

  Thioredoxin, thioredoxin reductase, and NADPH
• When is the ribonucleotide reductase complex functional?

  When cells are actively synthesizing DNA
• What is the conversion of dUMP to dTMP involved in?

  DNA synthesis
• What are the key steps in pyrimidine biosynthesis?

  • Synthesis from carbamoyl phosphate and aspartate
  • Ribose supplied by PRPP
  • Catalyzed by CPS-II
• What are the implications of a diet low in aspartate, glycine, and glutamine?

  • May or may not affect de novo biosynthesis
  • All three are non-essential amino acids
  • Can be synthesized from other amino acids
• What is the role of ribonucleotide reductase in nucleotide metabolism?

  • Reduces ribonucleotides to deoxyribonucleotides
  • Requires thioredoxin, thioredoxin reductase, and NADPH
  • Active during DNA synthesis
• What are the final products of pyrimidine degradation?

  • β-alanine
  • β-aminoisobutyrate
  • NH3
  • CO2