DNA structure Nucleic acids information required
- 1. 8.2 Structure of DNA KEY CONCEPT DNA structure is the same in all organisms.
- 2. 8.2 Structure of DNA DNA is composed of four types of nucleotides. • DNA is made up of a long chain of nucleotides. • Each nucleotide has three parts. – a phosphate group – a deoxyribose sugar – a nitrogen-containing base phosphate group deoxyribose (sugar) nitrogen-containing base
- 3. 8.2 Structure of DNA • The nitrogen containing bases are the only difference in the four nucleotides.
- 4. 8.2 Structure of DNA Watson and Crick determined the three-dimensional structure of DNA by building models. • They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside.
- 5. 8.2 Structure of DNA • Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. – Franklin’s x-ray images suggested that DNA was a double helix of even width. – Chargaff’s rules stated that A=T and C=G.
- 6. 8.2 Structure of DNA T A C G Nucleotides always pair in the same way. • The base-pairing rules show how nucleotides always pair up in DNA. • Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. – A pairs with T – C pairs with G
- 7. 8.2 Structure of DNA • The backbone is connected by covalent bonds. hydrogen bond covalent bond • The bases are connected by hydrogen bonds.