Molecular Basis of Inheritance


  1. DNA is made up deoxyribonucleotides arranged in a double stranded chain.
  2. Three components of a nucleotide are (i) Sugar (ii) Phosphate (iii) N2 bases
  3. Nucleotide – Phosphate = Nucleoside.
  4. Nitrogenous bases of DNA are Adenine (A), Thymidine (T), Guanine (G), and cytosine (C) Where A and G are purines; T and C are Pyrimidinines. RNA has uracil instead of Thymine
  5. The length of E.coli DNA is 4.6 × 106 BP and Human haploid DNA is 3.3 × 109 BP.
  6. The nucleotides in a DNA strand are connected to each other nucleotide by a phosphodiester bond (3 → 5 likage).
  7. Glycosidic linkage is created between N2 base and pentose sugar.
  8. The linkage between sugar and phosphate is made by covalent bond.
  9. The width of a DNA molecule is 20 A° (P – P), 11.1A° (Sugar – Sugar); 2.8 A° – 3 A° (H - bond)
  10. Length of a helix in a DNA is 34 A° Hence distance between 2 nucleotide in a DNA is 3.4A° As only 10 nucleotides are present in a helix of DNA.
  11. Watson and crick proposed the model of Double helical structure of DNA with the help of chargaff and franklin & wilkins.
  12. A pairs with T with 2H bonds; G pairs with C with 3H bonds; amount of T = amount of A; amount of G = amount of C 
    A+T/ G+C ratio is constant for the species, are the rule of chargaff.
  13. Franklin and wilkins performed X-ray crystallography to prove the crystalline nature of DNA, diameter, length and its helical nature.
  14. One end of DNA is represented by 5' as its 5th carbon atom possess free hydroxyl group. Other end of DNA is marked by 3' as its 3rd carbon atom possess free hydroxyl group.
  15. DNA runs antiparallel in nature. A, B, C, D [right handed] and Z [left handed] are the different types of DNA , in which type B is found in human beings.
  16. DNA is packed as chromosomes with the help of histone proteins (H1, H2A, H2B, H3, H4) in which H1 is linker DNA and rest proteins act as dimer finally to get aptamer structure.
  17. DNA is negatively charged which binds with positively charged histones which is made up of positively charged amino acids like lysine and Arginine.
Nucleotide Nucleoside
Adenine Adenosine
Thymine Thymidine
Guanine Guanosine
Cytosine Cytidine
Uracil Uridine

DNA in Prokaryotes is Circular and eukaryotes is linear.

Watch this video for the topic from 1:00 to 27:05

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