DNA Replication and Genetic Code
Semi-Conservative Replication:
- Called semi-conservative because one strand of the new DNA is conserved from the original DNA, and the other strand of the new DNA is made from new complementary bases.
- DNA Helicase enzyme 'unzips' the double helix by breaking the hydrogen bonds between bases.
- Free nucleotides rush to bond to available complementary bases.
- Once aligned, DNA polymerase enzyme joins the nucleotides together by forming phosphodiester bases along the sugar-phosphate backbone, running 3' to 5'.
- On the strand running antiparallel, ligase enzyme joins the nucleotides together in sections called okazaki fragments.
Key Terms:
Continuous Replication: Where the phosphodiester bonds in the sugar-phosphate backbone are formed in an unbroken chain, not formed as small sections.
Discontinuous Replication: Where the phosphodiester bonds in the sugar-phosphate backbone are formed in segments, which are then joined together.
Mutation: When a random change in the sequence of bases occurs because there is an error in DNA replication.
Genetic Code: The sequence of DNA base pairs which carries the instructions for the synthesis of proteins.
Codon: A series of three base pairs which codes for a single amino acid.
Gene: A section of DNA which contains the complete sequence of bases/codons that codes for an entire protein.
Degenerate Code: When a single amino acid can be coded for by a variety of codons.
DNA Code Wheel:
- Can be used to determine which codon codes for which amino acid.
- Read from the centre outwards.