Nucleotides Structure and Composition

Nucleotides

• Nucleotides are the basic structural units of nucleic acids
• Composed of three components: nitrogenous base, pentose sugar, and phosphate
• Nitrogenous bases are of two types: purines (double-ring structure: Adenine and Guanine) and pyrimidines (single-ring structure: Cytosine, Thymine, or Uracil)

Polymerization of Nucleotides

• Forms a polynucleotide chain with a negative sugar-phosphate backbone
• Free 5' phosphate on one end (5' end) and free 3' hydroxyl on the other end (3' end)
• Nitrogenous bases are attached to the backbone and are free to pair with nitrogenous bases of other polynucleotide chains

Free Radicals

• A molecule or atom with an unpaired electron in its outermost orbital
• Highly reactive and has an extremely short half-life of microseconds
• Reacts randomly with any molecule to achieve stability by either accepting or donating an electron

ROS and Oxidative Damage

• Incomplete reduction of oxygen produces ROS (superoxide, hydroxyl, perhydroxyl) and H2O2 (a highly reactive ROS)
• Tissue damage caused by oxygen radicals is called oxidative damage

Antioxidants

• Substances that protect against cellular injury by ROS or other oxidants by scavenging them
• Can be supplemented from outside (in vitro antioxidants)
• Examples:
  • Enzymes: glutathione peroxidase, catalase, superoxide dismutase (SOD)
  • Non-enzymes: transferrin, ferritin, ceruloplasmin, albumin, glutathione, uric acid, bilirubin, ubiquinone, vitamins E and C, beta carotene, selenium

Vitamin E

• Fat-soluble antioxidant absorbed in the small intestine
• Primary defender against effects of free radicals in the body
• Stored in liver and fat cells, protecting components of the cell and their membrane from destruction

Vitamin C

• Water-soluble antioxidant that gives up electrons easily
• Helps reactivate other antioxidants like vitamins E and C, glutathione, urate, and beta carotene
• Protects oxygen and iron from oxidation, and arteries from oxidative damage
• Works in aqueous environments, breaking chain reactions and scavenging reactive oxygen and nitrogen species

Flavonoids

• 20 times stronger antioxidant than vitamin C and 50 times stronger than vitamin E
• Water-soluble and able to attach to cells and their proteins for up to 72 hours, protecting them from oxidation and free radical damage
• Able to cross the blood-brain barrier