DNA jigsaw Sketch the pieces joined in the

DNA jigsaw… Sketch the pieces joined in the correct arrangement for DNA. Label: a sugar, a phosphate and a base pair

Answer… (are there other possibilities? )

Nucleic Acids • DNA is a type of nucleic acid – deoxyribonucleic acid • DNA is a polymer (molecule made of many smaller units called monomers) • Individual unit called a nucleotide •

Nucleotide Structure 3 components: – Deoxyribose sugar – Phosphate – Nitrogenous base (always contains nitrogen) Phosphate Stay the same sugar Pentose sugar (5 Carbon atoms) base Changes Contains nitrogen & carbon

Nucleotide Structure O O=P-O O 5 CH 2 O Phosphate Group N C 1 C 4 Sugar (deoxyribose) C 3 Pentose C 2 Nitrogenous base (A, G, C, or T)

Nucleotide Structure Phosphate Group O O=P-O O My house (sugar), a garage (base) and a satellite dish 5 (phosphate group) CH 2 O N C 1 C 4 Sugar (deoxyribose) C 3 Pentose C 2 Nitrogenous base (A, G, C, or T)

4 Bases • Purines – – Double ringed structure • Pyrimidines – – Single ringed structure

Watson and Crick Problem of how the base pairs match up: • Cut out base pairs on cards • Tried to line them up to study whether intermolecular forces might hold them together • Recruited the help of a chemist!!

The bigger picture… Can you suggest any other reasons that Adenine always pairs with Thymine and Cytosine always pairs with Guanine? Consider the size of the base pairs relative to the distance between the sugarphosphate backbone.

DNA Double Helix 5 O 3 3 P 5 O O C G 1 P 5 3 2 4 4 2 3 P 1 T 5 A P 3 O O P 5 O 3 5 P

4 Bases • Purines – – Double ringed structure • Pyrimidines – – Single ringed structure

Complementary Base Pairing *Purines always pair with pyrimidines* A joins to T C joins to G

Tell me… 4 3 2 1 names of bases in DNA components of a nucleotide sides of a DNA strand are called strand of DNA forms a structure called