chemical nature of DNA

• friedrich miescher discovered that nucleic acid is made up of nitrogenous bases, sugars and phosphates
• friedrich miescher isolated nuclein from pus cells
• erwin chargaff found the base composition of dna was constant between different species but varied within one organism
• levene showed that there are two types of purines (adenine and guanine) and pyrimidines (cytosine and thymine)
• rosalind franklin used x-ray diffraction to show that dna has a helical structure with a diameter of 20nm
• these were the first steps towards understanding the structure of dna
• rosalind franklin used x-ray diffraction to show that dna has a helical structure with two strands held together by hydrogen bonds
• james watson and francis crick proposed the double helix model of dna based on rosalind franklins data
• the double helix model consists of two antiparallel chains of deoxyribonucleotides joined by hydrogen bonds between complementary bases (adenine pairs with thymine and cytosine pairs with guanine)
• the complementary base pairing means that if the sequence of one strand is known then the other can be deduced
• dna contains four nitrogenous bases - adenine, thymine, cytosine and guanine
• the sugar deoxyribose forms the backbone of the dna molecule
• james watson and francis crick proposed the double helix model of dna based on their knowledge of chemistry and biology
• james watson and francis crick proposed the double helix model of dna which is made up of two antiparallel chains joined by complementary base pairs
• watson and cricks model suggested that adenine pairs with thymine through two hydrogen bonds while cytosine pairs with guanine through three hydrogen bonds
• the double helix is stabilised by weak intermolecular forces such as van der waals interactions and hydrophobic interactions