B3 - DNA

Chromosomes Chromosomes are made from long molecules of coiled up DNA Double helix structure. Both sections are made up of small groups called nucleotides Each nucleotide has a small molecule called a base Bases are A, C, T, G The bases form cross links to the other stand and this keeps them tightly together A always goes with T, C goes with G This is called complementary base pairing

Watson & Crick First scientists to model DNA (1953) Used data from other scientists Including x-ray data showing the double helix structure Bases occur in pairs By putting this data together they built a model showing what DNA looks like Don't forget, new discoveries aren't widely accepted straight away, other scientists need to repeat the work to prove results are reliable

DNA can replicate itself DNA copies itself every time a cell divides, so each cell has the full amount of DNA The DNA has to unwind  before it can copy itself, so it forms two strands There are new nucleotides which float freely in the nucleus then join by using complementary base-pairing, which makes an exact copy of DNA on the other strand The result is two double stranded molecules of DNA that are identical to the original one.

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