Nucleic acid

• DNA molecules


  Exist as a double helix, proposed by Watson and Crick in 1953
• Chargaff's rules


  • Two long polynucleotide chains are coiled around a central axis, forming a right handed double helix
  • The two DNA strand are antiparallel, runs in opposite direction
  • The base of both chains lie perpendicular to the axis, and they are stacked on one another
  • The nitrogenous bases of opposite chains are paired as the result of the formation of a hydrogen bond in DNA
  • Each complete turn of helix is 34 A long
  • The double helix has a diameter of 20 A
• Elements in nucleic acids

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Phosphorus
• Nucleotides


  The building blocks of nucleic acids
• Components of nucleotides


  • Phosphate group
  • Pentose sugar
  • Nitrogenous bases
• Nitrogenous bases in DNA

  • Adenine
  • Guanine
  • Thymine
  • Cytosine
• Nitrogenous bases in RNA

  • Adenine
  • Guanine
  • Uracil
  • Cytosine
• Purines


  Heterocyclic aromatic compound with a pyrimidine ring fused with an imidazole ring, includes Adenine and Guanine
• Pyrimidines


  Heterocyclic aromatic compound with a pyrimidine ring, which has nitrogen atoms at the 1 and 3 position, includes Cytosine, Thymine, Uracil
• Chargaff's rule: Purine = Pyrimidine. A-T, G-C.
• DNA


  The "hereditary molecule", contains the genes and the genetic code
• DNA replication


  1. Helicase (unzipping enzyme)

  2. Primase (the initializer)

  3. DNA polymerase (the builder)

  4. Ligase (the gluer)
• Gene


  A particular segment of a DNA molecule or chromosome, contains the instructions (the "recipe" or "blueprint") that will enable a cell to make what is known as a gene product
• The genetic code consists of four letters: A, T, G, and C.
• RNA


  Participate in the conversion of the genetic code into proteins and other gene products
• Transcription


  RNA polymerase (DNA-dependent RNA polymerase)
• Types of RNA


  • messenger RNA (mRNA) (carry genetic information from the DNA of the gene)
  • ribosomal RNA (rRNA) (non-specific sites of protein synthesis during translation)
  • transfer RNA (tRNA) (carries amino acids to the ribosome during translation)
• Central dogma


  DNA → (transcription) → mRNA → (translation) → protein
• The amino acids in a polypeptide chain are connected by covalent bonds and peptide bonds