Nucleotides and Nucleic Acids Overview

Nucleotides: Building Blocks of Nucleic Acids

• Nucleotides are the building blocks of DNA and RNA.
• They are not essential nutrients, as the body can synthesize them.
• They are crucial components of ATP, the cell's primary energy source.
• Nucleotides are also part of coenzymes like NAD, NADP, and FAD.
• They form cAMP and cGMP, acting as secondary messengers for hormones.
• Nucleotides regulate metabolic pathways by inhibiting or activating enzymes.
• Purine and pyrimidine bases in nucleotides can be synthesized de novo or through salvage pathways.
• Nucleic acids are linear polymers, storing and transmitting genetic information for growth and reproduction.
• Purines include adenine and guanine; pyrimidines include cytosine, uracil, and thymine.
• Thymine and uracil differ; only thymine has a methyl group.
• Some organisms have unusual DNA/RNA bases (modified bases), e.g., in some viruses and tRNA. Modifications include methylation, acetylation, reduction, and glycosylation.

Nucleosides

• A nucleoside forms when a pentose sugar (ribose or deoxyribose) links to a purine or pyrimidine base via an N-glycosidic bond.
• Ribose forms ribonucleosides; deoxyribose forms deoxyribonucleosides.
• Examples: Adenine forms deoxyadenosine, guanine forms deoxyguanosine, cytosine forms deoxycytidine, thymine forms deoxythymidine, uracil forms uridine, adenine in RNA forms adenosine, etc.
• A table would show the relationship.

Nucleotides: Building Blocks

• Nucleotides are formed when one or more phosphate groups attach to a nucleoside.
• Each nucleotide has a base (purine or pyrimidine), a pentose sugar (ribose or deoxyribose), and phosphate groups.
• Phosphate groups attach to the 5' carbon of the pentose sugar via ester linkages.
• The phosphate groups impart a significant negative charge to DNA and RNA.

Nucleotide Synthesis Pathways

• Three pathways synthesize nucleotides:
  • De novo synthesis: Synthesizes nucleotides from metabolic precursors (amino acids, ribose-5-phosphate, CO2, one-carbon units). These enzymes are found in liver, small intestine, and thymus.
  • Salvage pathways: Recycles free bases or nucleosides from broken-down RNA and DNA, to recover bases/nucleosides.
  • Conversion of ribonucleotides to deoxyribonucleotides: Occurs at the level of nucleoside diphosphates, converting ADP, CDP, GDP, and UDP. Ribonucleotide reductase (RR) enzyme is responsible.

Naming Nucleotides

• adding a phosphate to a pentose= Monophosphates (e.g., AMP, adenylate).
• adding a second or third phosphate=Diphosphates (e.g., ADP) or Triphosphates (e.g., ATP).