DNA Structure

• Friedrich Miescher - He discovered nucleic acids upon isolation of “nuclein” from white blood cells.
• DNA - isolated material
• Nucleic acids - biomolecules that play important roles in the storage and expression of genetic information.
• They are macromolecules composed of the monomers called nucleotides.
• The genetic information is stored in the cell nucleus.
• Components of nucleotides:

  • phosphate sugar
  • 5-c sugar
  • nitrogenous base
• bonds within nucleotides:

  • Glycosidic bond
  • Ester bond
• Glycosidic bond attaches the base to the first C of sugar
• Ester bond attaches the phosphate to the first C of sugar
• Ester and glycosidic bonds occur within a nucleotide
• Phosphodiester linkages

  connect the nucleotides.
• A nucleotide is connected to its adjacent nucleotides via two ester bonds.
• Phosphate group is bonded to the 3′ carbon of sugar.
• Nucleic acids can either be a

  • DNA (deoxyribonucleic acid)
  • RNA (ribonucleic acid)
• difference of DNA and RNA:

  nitrogenous bases and the 5-C sugar.
• Nitrogenous bases can either be

  • purines (two-ringed)
  • pyrimidines (single-ringed).
• DNA and RNA have the same bases except for thymine in DNA and uracil in RNA.
• nucleic acids differ in 5-C sugar.
• DNA has the sugar deoxyribose, while RNA has ribose. (5-c sugar)
• DNA and RNA sugars differ in the second carbon atom.
• Erwin Chargaff established

  rules about DNA composition.
• The Chargaff rule - rules about DNA composition
• 1:1 ratio between A & T and C& G
• The Chargaff rule -

  • The amount of A almost equal to T
  • The amount of G almost equal to C
• The base pairings in DNA help protect and conserve its genetic information.
• The DNA stores genetic information in the form of nucleotide sequences.
• The strands of DNA run in opposite directions making them antiparallel
• Coding strand: runs in 5′ to 3′ direction; the strand that is expressed
• Template strand: runs in 3′ to 5′ direction
• The DNA double helix is a twisted, right-handed, staircase.
• Base pairs: the rungs of the ladder
• The twisting and rigidity of the DNA form grooves or gaps.
• Minor groove: backbones are closer; base more hidden
• DNA is contained in cell nucleus.
• James Watson and Francis Crick - used different data sets such as that of Rosalind Franklin and Erwin Chargaff.
• Rosalind Franklin, alongside Raymond Gosling, obtained the Photograph 51 via X-ray crystallography.
• Sugar-phosphate: the sides of the ladder
• James Watson and Francis Crick - first proposed the double helical structure of DNA.
• Major groove: backbones are farther; bases more exposed
• The symmetric patterns generated were interpreted as the DNA structure