Self Replication

• (1) DNA Helicase breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands.
• (2) Each original single strand acts as a template for a new strand. Free-floating DNA nucleotides join to the xposed bases on each original template strand by complementary base pairing - GCAT
• (3) The nucleotides of the new strand are joined together by the enzyme DNA Polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand. The strands twist to form a double-helix.
• (4) Each new DNA molecule contains one strand from the original DNA molecule and one new strand.
• This type of copying is called semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA.
• DNA replication is really accurate - it has to be, to make sure genetic information is conserved each time the DNA is replicated.
• Every so often though, a random spontaneous mutation occurs. A mutation is any change to the DNA base sequence. Mutations don't always have an effect, but they can alter the sequence of amino acids in a protein. This can cause an abnormal protein to be produced. The abnormal protein might function better then the normal protein - or may not function.