Molecular Basis of Inheritance

Molecular Basis of Inheritance

• DNA is identified as the primary genetic material in most organisms, with RNA also serving a genetic role in some viruses.
• DNA's structure involves long polymers of deoxyribonucleotides, characterized by the number of nucleotide pairs, also known as base pairs.
• Specific examples of DNA length include:
  • Bacteriophage φ ×174: 5386 nucleotides
  • Bacteriophage lambda: 48,502 base pairs
  • Escherichia coli: 4.6 million base pairs
  • Human haploid DNA: 3.3 billion base pairs

Structure of DNA

• Each nucleotide comprises three components:

  • A nitrogenous base (purines: Adenine, Guanine; pyrimidines: Cytosine, Thymine in DNA, Uracil in RNA)
  • A pentose sugar (deoxyribose in DNA, ribose in RNA)
  • A phosphate group

• Nitrogenous bases link to the 1' carbon of the pentose sugar via N-glycosidic bonds, forming nucleosides (e.g., adenosine, guanosine).

• When a phosphate group is attached to the 5' carbon of a nucleoside through a phosphoester bond, a nucleotide is formed.

Formation of Polynucleotide Chains

• Nucleotides are joined by 3'-5' phosphodiester linkages, creating dinucleotides and longer polynucleotide chains.
• Each polynucleotide chain has a defined orientation with:
  • A free phosphate group at the 5' end
  • A free hydroxyl group at the 3' end

Transcription and Translation

• Replication of DNA leads to transcription, where RNA is synthesized from DNA templates.
• The genetic code derived from DNA determines the sequence of amino acids in proteins through translation.

Human Genome Project

• Recent developments in genomics, including comprehensive sequencing of the human genome, have significant implications for genetics and biotechnology.

RNA Functions

• In addition to acting as the genetic material in some viruses, RNA serves multiple roles:
  • Messenger RNA (mRNA): carries genetic information.
  • Adapter and structural roles in protein synthesis.
  • Some RNA molecules exhibit catalytic properties.