vocab

semi-conservative - describes the nature of DNA replication

  • one original strand will serve as a template for DNA replication

  • this means that the new double strand of DNA has one original strand of DNA & one newly synthesised strand of DNA

DNA helicase - is an enzyme that, in eukaryotes, will break the hydrogen bonds holding together the nitrogenous bases on two DNA strands

  • this separates each DNA strand, unwinding the double helix

    • this forms replication fork

single stranded binding proteins - proteins that bind to single stranded DNA, preventing the strands from rebinding

DNA polymerase III - is an enzyme that will move along the DNA strands

  • it will build a new DNA strand by using the existing one as a template, & adding free nucleotides based on complementarity

  • also proofreads replicated strand

Polymerase Chain Reaction (PCR) - a technique where small amounts of DNA are amplified into larger quantities

  • the desired DNA sequence is placed in a chamber that contains:

    • free nucleotide triphosphates

    • a heat-stable version of DNA polymerase called Taq polymerase

      • this enzyme doesn’t denature at high temps

    • primers

Gel electrophoresis - technique that allows key features of DNA to be identified

  • restriction endonucleases are used to get smaller pieces of DNA

    • these are enzymes that cut the backbone of the DNA molecule at specific sites

  • uses an electrical current to move the DNA molecules through a gel

  • DNA molecules are negatively charged, so they’re attracted to the positive electrode

  • the gel is porous so small pieces of DNA can move further towards the electrode

Leading strand - the strand that runs in a 5’ to 3’ direction

  • replication is continuous

  • DNA replication is initiated by RNA primer only one

    • so RNA primer placed only once

Lagging strand - runs in 3’-5’ direction (opposite)

  • replication is discontinuous, as DNA polymerase III will form Okazaki fragments

  • DNA replication initiated by RNA primer multiple times

    • so RNA primers are placed at regular intervals

Okazaki fragments - short pieces of replicated DNA, that’re formed on the lagging strand

Gyrase - moves ahead of helicase, relieving tension created from unwinding & separating

DNA primase - attaches RNA primers to template strand

  • in leading strand - requires only 1 RNA primer

  • in lagging strand - requires multiple primers

RNA primers - serves as a starting point for DNA replication

DNA polymerase I - removes the RNA nucleotides from the primers & replaces them with the correct nucleotides

DNA ligase - catalyzes formation of phosphodiester bonds between the Okazaki fragments, forming a complete strand