The Enzymes of Replication – DNA Structure and Replication

by Georgina Cornwall, PhD

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    00:01 So now we need to look a little more closely at some of the players involved in synthesis.

    00:06 To start with we know we are unwinding the DNA and unzipping, in order to have access to the bases and this can cause a few problems. First of all, helicase is the first enzyme I will introduce you to. Recall that the ending -ase always mean enzyme. We have helicase, so this is an enzyme that unwinds the helix, great name for it right? So it unwinds the helix much like pretty old telephone when the telephone wire got twisted up maybe you have experienced with the blow dryer. The blow dryer cord gets all twisted up.

    00:47 That's supercoiling. DNA does the same thing. When we unzip, it starts to supercoil and so we need to have enzyme to fix that. It is another enzyme that has an -ase ending because enzymes are -ase and so these unwinding of this torsional strain is going to happen with the enzyme gyrase. Gyrase is to move around and so gyrase will unwind this supercoiling by simply snipping the DNA letting the supercoil release and gluing it back together. Gyrase and helicase work together to make sure we don't have supercoiling. There is a few more players involved in this whole process. We can see that there are a number of different enzymes that come together to form this replisome. First of all, we will introduce primase because it comes first. Primase is the enzyme that lays downs primers. We'll define them and then we will put them into place. Then we have it laying down RNA primers and then we have the DNA polymerase. There are three types of DNA polymerase. I will introduce you to two of them here. DNA polymerase III is the primary DNA polymerase and it is able to lay down nucleotides in sequence along the strand reading from three prime to five prime doing its job just like it is supposed to. And then we have DNA polymerase I who is involved in covering up the primers that DNA primase laid down. DNA polymerase I covering primers, DNA polymerase II we are not going to introduce here, but he is involved in doing some excision repair and such when we have DNA mutations. DNA ligase, like ligand to stick. It is like a tube of glue. DNA ligase will glue Okazaki fragments back together. I think we are about

    About the Lecture

    The lecture The Enzymes of Replication – DNA Structure and Replication by Georgina Cornwall, PhD is from the course Understanding Genetics.

    Included Quiz Questions

    1. DNA polymerase I
    2. DNA polymerase III
    3. Primase
    4. Gyrase
    5. Topoisomerase
    1. DNA polymerase ---- RNA primer synthesis
    2. Helicase ---- unwinding of the DNA helix
    3. DNA gyrase ---- relieves torsional strain in DNA supercoils
    4. Primase ---- primer synthesis
    5. DNA ligase ---- glue Okazaki fragments

    Author of lecture The Enzymes of Replication – DNA Structure and Replication

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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