DNA replication

• why does DNA replicate

  DNA copies itself before cell division so that each new cell has the full amount of DNA. This is important for making new cells and for passing genetic information from generation to generation
• 1. DNA helicase (an enzyme) 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 exposed bases on each original template strand by complementary base pairing

  A with T and G with C.
• 3. The nucleotides on 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. Each new DNA molecule contains one strand from the original DNA molecule and one new strand.
• semi-conservative replication 


  half of the strands in each DNA molecule are from the original piece of DNA
• DNA replication is really accurate. 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 than the normal protein - or it might not work at all.