The document summarizes the structure of DNA. It describes that: 1) James Watson and Francis Crick described DNA as a double helix structure. 2) A DNA nucleotide contains a deoxyribose sugar, phosphate group, and a nitrogen base (adenine, cytosine, thymine, or guanine). 3) In DNA, adenine pairs with thymine and guanine pairs with cytosine to form the rungs of the DNA ladder structure.

1. The structure of DNA

2. Watson & Crick James Watson and Francis Crick described the structure of the DNA molecule as a double helix Their work was aided by pictures of the DNA molecule taken Rosalind Franklin . In 1962 Crick & Watson received the Nobel Prize for their pioneering work on the structure of the DNA molecule.

3. DNA- The molecule of Heredity We have already learned a little on DNA We know it is a complex polymer called a nucleic acid We know that nucleic acids are made up of smaller base units called nucleotides.

4. DNA nucleotides A DNA nucleotide is made up of three main parts Deoxyribose (simple sugar) Phosphate group Nitrogen base There are 4 bases Adenine – A Cytosine- C Thymine- T Guanine- G

5. DNA Bases Adenine (A) pairs with Thymine (T) Guanine (G) pairs with Cytosine (C)

7. Chains of Nucleotides In DNA nucleotides do not exist as individual molecules Many nucleotides are connected to make nucleic acids Nucleotides combined to form two long chains (making one molecule) Each chain of nucleotides contains single nucleotides connected to each other

8. Structure of DNA Chain of nucleotides, the sugar of one nucleotides is joined to the phosphate group of the next nucleotide by a covalent bond. The two chains of nucleotides in a DNA molecule are held together by hydrogen bonds between the bases. This pairing produces a long, two stranded molecule . The sides of the ladder are formed by the sugar and phosphate units, while the rungs of the ladder are the pairs of bases. Not only is the DNA molecule in the form of a ladder but it is twisted into a double helix.