RNA Polymerase – Complexity of RNA Structure

by Kevin Ahern, PhD

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    00:01 Now RNA polymerase, of course, plays an important role an essential role in transcription; because, without RNA polymerase cells can't make RNA.

    00:10 Eukaryotic cells have a different setup for RNA polymerases then prokaryotic cells.

    00:17 In prokaryotic cells, again, it's a simpler world.

    00:20 All of the transcription in the prokaryotic cells is done by one RNA polymerase.

    00:25 It does all the work that's there.

    00:27 Eukaryotes breakdown function by different polymerases.

    00:31 So many RNA polymerases that are made have a hand structure and that hand structure is like we saw with the DNA polymerases in a previous lecture.

    00:43 That hand is designed to hold onto a DNA.

    00:49 You can see the hand structure here in green.

    00:51 And RNA polymerases like DNA polymerases only work in the 5 prime to 3 prime direction.

    00:59 Now one difference with RNA polymerase is they do not require a primer.

    01:03 DNA polymerases always require a primer. So RNA polymerases are simpler in that respect.

    01:11 Now another difference with RNA polymerases are at least 1 difference with the process of of transcription compare to DNA replication is that only one strand of the DNA template is copied.

    01:22 Now we can see on the right a representation of an RNA polymerase that is bound to a DNA and you can see that the strands have been peeled apart.

    01:32 You can also see on this figure that the strand that's being copied by the RNA polymerase and you can see the RNA coming off in red the strands that's being copied is called the template strand.

    01:43 Whereas the strand that is not being copied is called the coding strand.

    01:47 The transcript comes off of the DNA so for usually during transcription only a small region of the part being transcribed will have base pairs between the RNA and the DNA. The rest of it falls off the end as you see here.

    02:05 Now RNA polymerases in eukaryotic cells, as I said, are specialized in function.

    02:10 Eukaryotic cells or most eukaryotic cells have three different RNA polymerases.

    02:16 These have individual functions for making specific RNAs, as we shall see.

    02:20 Plants have as many as 5 and I won't go into that there.

    02:23 Prokaryotic cells, as I noted, only have one RNA polymerase.

    02:27 And some viruses actually encode their own RNA polymerase.

    02:31 Now if you think about that, that's an indication of the importance of the RNA and perhaps in the case of the virus the specific needs of the virus, for a specific type of RNA.

    02:45 The sigma subunit of the prokaryotic RNA polymerase, as I noted earlier, is the functional part of the polymerase it's really all this needed in most cases to help the RNA polymerase to bind to the DNA and make the transcript.

    02:59 In eukaryotic RNA polymerases we have numerous subunits but these subunits don't bind to promoters and that's again unlike the prokaryotic RNA polymerase.

    03:10 And last but important certainly from a medical perspective is the fact that eukaryotic RNA polymerases are susceptible to a poison called α-amanitin.

    03:20 α-amanitin is produced by some mushrooms and so you may have heard of people having issues with death cap mushroom.

    03:29 Death cap mushrooms create this toxic substance called α-amanitin and it is exquisitely a poison for RNA polymerase too.

    03:40 Very very tiny amounts of α-amanitin can stop the functioning of RNA polymerase too.

    03:45 If you have eaten death cap mushrooms and you don't get a liver transplant very shortly, you are probably not gonna be around.

    03:54 The RNA polymerases that I wanna discuss in eukaryotes are the three that we find in almost all eukaryotic cells and these are RNA polymerase I.

    04:02 RNA polymerase I is a polymerase that makes the large ribosomal RNAs.

    04:08 These include the 28S, the 18S and the 5.8S ribosomal RNAs.

    04:14 Now you will notice it says they are processed to that.

    04:16 That means that these ribosomal RNAs are made in larger molecules and then chopping and cutting of pieces and editing of that results in the final products here.

    04:27 The second RNA polymerase in eukaryotic cells is that of RNA polymerase II.

    04:31 Now RNA polymerase II is doing a bulk of the work in the cell it's making the messenger RNAs which, of course, are the RNAs that carry the genetic information to the ribosome for translation into proteins.

    04:44 They make most of the small nuclear RNAs that I will talk about later and the micro RNAs that are involved in helping to regulate gene expression.

    04:55 RNA polymerase III performs functions of making mostly the small RNAs in the eukaryotic cells.

    05:01 This includes the 5S ribosomal RNA, that's the smallest one, the transfer RNAs and other small RNAs that the cell may need.

    05:10 Well, with this presentation I have gone through the complexity of eukaryotic RNA synthesis as well as the discussion of the RNA polymerases that are involved in cells.

    05:21 In other presentations, I will go through in some more detail the different functions of RNA and the way that RNA is actually used to control its own gene expression.

    About the Lecture

    The lecture RNA Polymerase – Complexity of RNA Structure by Kevin Ahern, PhD is from the course RNA and the Genetic Code.

    Included Quiz Questions

    1. They have a hand structure like DNA polymerases
    2. They require a primer
    3. They operate like DNA polymerases, copying both strands simultaneously
    4. They primarily copy the coding strand
    1. rRNAs
    2. tRNAs
    3. mRNAs
    4. miRNAs
    1. α-amanitin
    2. Penicillin
    3. Class B beta-lactams
    4. Clavulanic acid
    5. Sulbactum

    Author of lecture RNA Polymerase – Complexity of RNA Structure

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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