Knowledge-3 NAN

• Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) are both nucleic acids.
• DNA and RNA are information carrying molecules.
• DNA holds genetic information
• RNA transfers genetic information from DNA to ribosomes
• Ribosomes are made from protein and RNA.
• both DNA and RNA are polymers of nucleotides.
• Structure of DNA:

  • A deoxyribose sugar
  • A phosphate group
  • one of the organic bases
  • double stranded molecule with a ladder like structure
  • phosphate backbones are held in place by pairs of complementary bases joined by hydrogen bonds.
  • double helix
• The organic bases are:

  • thymine
  • guanine
  • adenine
  • cytosine
• Structure of RNA:

  • A ribose sugar
  • A phosphate sugar
  • one of the organic bases except thymine which is replaced by uracil
  • short single-stranded molecule.
• structure of nucleotides:

  • a pentose sugar
  • nitrogen containing organic base
  • a phosphate group
• A condensation reaction between two nucleotides forms a phosphodiester bond.
• DNA replication: The semi-conservative replication of DNA ensures genetic continuity between generations of cells.
• DNA replication:

  1. The DNA unwinds, then DNA helicase breaks hydrogen bonds between the complementary base pairs
  2. the double helix unwinds and separates the two strands of DNA.
  3. New DNA nucleotides bind to exposed bases on the DNA template strand
  4. DNA polymerase catalyzes the condensation reaction that joins adjacent nucleotides.
• Semiconservative DNA replication:

  • DNA must be able to replicate exact copies of itself.
  • Watson and crick suggested the strands would separate and each produced a new helix.
  • This was confirmed by Meselson and stahl , who grew e.coli bacteria with radioactive-labelled nitrogen.