4A enzymes that manipulate DNA

• Endonuclease is a ride range of enzymes, also known as restriction endonucleases, that are responsible for cutting strands of DNA.
• Endonuclease enzymes target specific recognition sites.
• The endonuclease enzymes break the phosphodiester bond between two nucleotides in a polynucleotide chain.
• The cutting process is also known as restriction endonuclease digestion.
• (Restriction) endonuclease is any enzyme that acts like molecular scissors to cut nucleic acid strands at specific recognition sites.
• Endonucleases either create blunt or sticky ends.
• Blunt end endonuclease cut DNA in the middle of the recognition site, which result in a straight cut.

  Example enzymes: Alul and Haelll
• Sticky end endonucleases do not cut in the middle of the recognition site, resulting in a staggered cut with overhanging, unpaired nucleotides.

  Example enzymes: EcoRI and Hindlll
• Ligases are enzymes that join two fragments of DNA or RNA, acting like a molecular glue. Ligase enzymes catalyse the formation of a phosphodiester bond between two adjacent (close by) nucleotides.

  Ligase enzymes lack the specificity of restriction endonuclease meaning they can join together any blunt or sticky ends.
• Ligase enzymes have two types:

  DNA Ligase

  RNA Ligase
• DNA Ligase joined two DNA fragments
• RNA Ligase joins two RNA fragments
• Polymerase enzymes add nucleotides to DNA or RNA, which can lead to copying entire genes, because polymerases synthesise polymer chains from monomer building blocks.
• Two types of Polymerase enzymes:

  RNA polymerase

  DNA polymerase
• RNA polymerase is mainly used in the transcription of genes
• DNA polymerase is used in the replication or amplification of DNA
• Polymerases require a primer to attach to the start of a template strand of DNA. Primers are short single-stranded chained of nucleotides that are complementary to the template strand. Once attached to the primer, the polymerase enzyme can read and synthesise a complementary strand to the template strand in a 5' to 3' direction.