DNA also has a degenerate code which means that there is more than one triplet code for the same amino acid. This is useful because if mutations occur on the DNA base sequence, an alteration may not lead to the production of a different amino acid and in effect would be harmless- a silent mutation. .
DNA has to be able to replicate itself in order to transfer information, as it is the carrier of inherited information. DNA copies itself by semi conservative replication. This means that each new molecule of DNA contains one strand from the original DNA and one newly synthesized strand. Each chain acts as a template for the synthesis of a new complementary polynucleotide chain. The DNA molecule unwinds with the help of the enzyme DNA helicase, which helps break hydrogen bonds between complementary base pairs and separate the two strands. The new nucleotides in the nucleus bind with their complementary bases in each exposed chain. DNA polymerases are enzymes, which catalyze the formation of a new polynucleotide chain by complementary base pairing. Another enzyme involved in DNA replication are DNA ligases which join together small sections of polynucleotides together to speed up the rate of replication, as replication would take a long time if it started at one end and proceeded nucleotide by nucleotide along the entire length of the molecule, so instead the double helix opens up and replicates simultaneously at a number of different sites, with the DNA ligases joining the segments of DNA together. An experiment by Meselson and Stahl tested the hypothesis that DNA replication was semi conservative. They used bacteria raised in culture media containing N15, which is a heavy isotope of nitrogen. The bacteria incorporated the N15 in their DNA, making the DNA denser than normal. Then the bacteria were transferred to a N14 medium. As the bacteria continued to replicate their DNA, centrifugation results showed various different bands, as generations passed more N14 was being displayed on the banding rather than N15.
