Dna and Rna

DNA and RNA Structure

Scientist Contributions

  • Frederick Griffith (1928): Discovered transformation, indicating genetic material transfer.

  • Oswald Avery (1940): Identified DNA as the transforming agent in bacteria.

  • Martha Chase and Alfred Hershey (1952): Confirmed that viruses also contain DNA.

DNA Structure

  • Double Helix Model: Proposed by James Watson and Francis Crick (1950s).

    • DNA consists of two chains in a double helix shape.

    • Model developed with contributions from Rosalind Franklin and Maurice Wilkins' X-ray diffraction data.

DNA Nucleotides

  • Composition: DNA made of nucleotides consisting of:

    1. Five-carbon sugar (Deoxyribose)

    2. Phosphate group

    3. Nitrogenous bases: Adenine, Guanine, Thymine, Cytosine.

Nitrogenous Bases

  • Pyrimidines: Thymine and Cytosine (single-ring).

  • Purines: Adenine and Guanine (double-ring).

DNA Structure Details

  • Structure analogous to a spiral staircase.

  • Sugar and phosphate form the sides (handrails); bases form the steps.

  • Base pairs bonded by hydrogen bonds: A-T and C-G pairs.

  • Each full helix turn contains 10 nucleotide pairs.

Erwin Chargaff's Discoveries

  • Chargaff's Rules (1949): Amount of Adenine equals Thymine and Cytosine equals Guanine.

  • Complementary base pairs crucial for DNA structure and replication:

    • Pairs: A-T and C-G.

    • Helps DNA copy itself by using one strand as a guide for the other.

RNA Structure

  • Similar to DNA but differs in four main ways:

    1. Contains ribose sugar instead of deoxyribose.

    2. Contains uracil (U) instead of thymine (T).

    3. Usually single-stranded, with some double-stranded regions formed through base pairing (G-C, U-A).

    4. Generally shorter than DNA.