Decoding DNA: Genetics, Experiments, and Molecular Structure

Posted on Mar 5, 2025 in Biology

DNA (Deoxyribonucleic Acid): The genetic material that carries hereditary information. The central dogma of molecular biology is DNA → RNA → Proteins. These proteins, often polypeptides, form structures like enzymes, which participate in the formation and breakdown of biomolecules, including nucleic acids, lipids, carbohydrates, and proteins.

RNA (Ribonucleic Acid): Another type of nucleic acid essential for various biological roles.

Genotype: The genetic information of an organism.

Phenotype: The observable characteristics of an organism, resulting from the interaction of the genotype and the environment.

The relationship between genotype, protein, and phenotype is that the expression of the genotype shapes the proteins and/or enzymes, which in turn give rise to the phenotype.

Key Experiments in DNA Discovery

Griffith’s Experiment

Griffith’s experiment involved Streptococcus pneumoniae, which causes pneumonia. There were two strains:

  • Strain S (Smooth): Virulent, causing pneumonia and death.
  • Strain R (Rough): Non-virulent.

The experiment:

  1. Strain S (heat-killed) + Strain R (live) were injected into a mouse.
  2. The mouse died.
  3. Blood samples from the dead mouse revealed live Strain S bacteria.

Avery Experiment

Avery’s experiment further investigated the transforming principle:

Enzymes were used to degrade different biomolecules:

  • Lipases, nucleases, proteases, and carbohydrases + Strain R: Bacterial transformation was observed when DNA was present.
  • When nucleases were added, bacterial transformation did not occur.

This demonstrated that DNA is the transforming principle.

The Watson and Crick Model

The Watson and Crick model describes the structure of DNA:

  • Phosphate (P), ribose (sugar) (R), and a nitrogenous base (BN) form the nucleotide.
  • Nitrogenous base pairings: Adenine (A) = Thymine (T) (2 hydrogen bonds), Cytosine (C) = Guanine (G) (3 hydrogen bonds).
  • DNA consists of a double chain of nucleotides.

Organization of DNA

Example DNA sequence: agtggaattctatcga – tcaccttaagatagct

  • Chromosome: DNA condensed with histone proteins.
  • Gene: A DNA sequence that codes for a specific protein.
  • Allele: A variant form of a gene.
  • Mutations: Changes in the DNA sequence that can result in altered protein function and potentially a different phenotype.