nucleotide
Summary
Nucleotides are the fundamental building blocks of nucleic acids (DNA and RNA), consisting of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. They serve crucial roles in energy metabolism (ATP), cellular signaling (cAMP), and genetic information storage/transmission.
Detail
A nucleotide is composed of three components: (1) a nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine in DNA, uracil in RNA), (2) a pentose sugar (ribose in RNA, deoxyribose in DNA), and (3) one to three phosphate groups. Nucleotides function as monomers that polymerize to form nucleic acids through phosphodiester bonds between the 3'-OH of one sugar and the 5'-phosphate of the next. Beyond structural roles in DNA/RNA, nucleotides serve as energy currency (ATP, GTP), second messengers (cAMP, cGMP), coenzymes (NAD+, FAD), and metabolic regulators. Nucleotide synthesis occurs via de novo pathways (starting from simple precursors) and salvage pathways (recycling preformed bases). Defects in nucleotide metabolism can lead to immunodeficiencies (SCID), gout (purine metabolism disorders), or cancer (altered DNA synthesis/repair).
Sources
- Lippincott's Illustrated Reviews: Biochemistry
- First Aid for the USMLE Step 1
- Lehninger Principles of Biochemistry
- Medical Biochemistry by Baynes & Dominiczak
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