DNA : Structure of Eukaryotic DNA
In 1869, Friedrich Miescher separated a cellular substance from the nuclei of pus cells and called it 'Nuclein'.
Subsequent studies showed that this material has acidic properties and hence it was renamed as "nucleic acid".
Deoxyribo nucleic acid (DNA) and ribonucleic acid (RNA) are the two major types of nucleic acids found in cells.
DNA is a long polymer of deoxyribonucleotides.
The length of DNA is usually defined as number of nucleotides (or a pair of nucleotide referred to as base pairs) present in it.
For example,
- Bacteriophage: φ 174 = 5386 nucleotides,
- Bacteriophage lambda = 48502 base pairs (bp),
- Escherichia coli = 4.6 × 106 bp, and
- Human = 3.3 × 109 bp.[Haploid]
Chemical components of nucleic acids:
Sugar (Ribose or Deoxyribose), Phosphate group and Nitrogen base.
Sugar
Pentose sugar - deoxyribose (C5H10O4 ) or ribose (C5H10O5 ) .
It is a five carbon compound and has pentagonal ring structure.
Phosphate group
It is actually phosphoric acid. (H3PO4).
It has three active -OH groups of which two are involved in strand formation.
Nitrogen bases
These are cyclic compounds made up of carbon, hydrogen, oxygen and nitrogen atoms.
- The bases are named adenine (A), thymine (T), cytosine (C), guanine (G) and uracil (U).
- These are classified into two groups- Purines and Pyrimidines.
- Adenine and guanine are double ring compounds called Purines
- Thymine and Cytosine and Uracil are single ring compounds called Pyrimidines.
- Uracil is absent in DNA and present in RNA
Nucleoside, Nucleotide and Nucleic acid
Pentose sugar + Nitrogen base = Nucleoside
Pentose sugar + Nitrogen base + Phosphate = Nucleotide
Nucleoside + Phosphate = Nucleotide