1 DNA 2 DNA stands for deoxyribonucleic acid

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DNA 2 DNA stands for deoxyribonucleic acid Facts 1. This chemical substance is present in the nucleus of all cells in all living organisms 2. DNA controls all the chemical changes which take place in cells 3. The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA 4. The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA

Nucleotide Definition: DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Parts: 1. a sugar called deoxyribose 2. a phosphate group -PO 4 and… 3. a Nitrogen base 3

6 Nucleotides The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide PO 4 adenine deoxyribose

5 The bases The Nitrogen bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Nucleotide Facts -1 10 The bases always pair up in the same way Adenine forms a bond with Thymine Adenine Thymine and Cytosine bonds with Guanine Cytosine Guanine

Nucleotide Facts - 2 7 PO 4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain PO 4 sugar-phosphate backbone + bases

Nucleotide Facts - 3 In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases 8

Nucleotide Bonding PO 4 C G PO 4 T A A T PO 4 A T PO 4 C G PO 4 T A PO 4 G C PO 4 C G 9

13 The paired strands are coiled into a spiral called A DOUBLE HELIX

14 THE DOUBLE HELIX bases sugar-phosphate chain

Replication 1. Before a cell divides, the DNA strands unwind and separate (during late Interphase) 2. Each strand makes a new partner by adding the appropriate nucleotides 3. The result is that there are now two doublestranded DNA molecules in the nucleus 4. So that when the cell divides, each nucleus contains identical DNA (after telophase) 5. This process is called replication 16

17 PO 4 The strands separate PO 4 PO 4 PO 4 PO 4

Each strand builds up its partner by adding the appropriate nucleotides PO 4 PO 4 PO 4 PO 4 PO 4 PO 4 18 PO 4 PO 4