Translation – DNA, RNA and the Genetic Code

by Kevin Ahern, PhD

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    00:01 RNA's. The ribosomal RNA of large subunit also contains 31 different proteins.

    00:01 Translation, the synthesis of protein occurs in three phases, initiation, which is where the ribosome assembles and this assembly process involves putting the start codon, which is AUG in the right place in the ribosome so the whole process can get started.

    00:18 Elongation occurs as the ribosome moves down the messenger RNA, one codon at a time and reading that sequence, attaches one amino acid to the next amino acid, to the next amino acid according to what the genetic code specifies. This process occurs five prime to three prime, starting near the five prime end of the messenger RNA and moving in the three prime direction.

    00:45 Last there's termination and termination happens when a stop codon appears in the ribosome, now the ribosome knows this is the place to let everything go.

    00:56 This figure schematically shows a ribosome and I want to step you through the process in terms of doing this. We will focus pretty much on the elongation phase because the assembly is a little bit complicated. This shows the large ribosomal subunit in light green on the top and the small ribosomal subunit in dark green on the bottom. Spanning through in between those two subunits is a strand of messenger RNA that you can see that's in yellow with some other colors of blue and beige within there. Also in the large subunit above, you can see some transfer RNAs that are coming in carrying individual amino acids. So there's the messenger RNA shown in yellow that I've described and here are the transfer RNAs that are coming into the large subunit as you can see. There are actually three places in the large subunit where the transfer RNAs can come in, the place where these are coming in is known as the A site, this is where the new transfer RNAs come in and the place where the previous transfer RNA was at is called the P site. The third site that's there is the place where the transfer RNA exits and that's known as the E site. So we see amino acids that are attached to the individual transfer RNAs, the transfer RNAs are bringing them to the point of translation. We see the entry of the tRNA going into the ribosome and this is actually traveling in this figure down into the ribosome. We can see that the transfer RNA anti-codon is pairing base pairs with the codon of the messenger RNA. And as I noted previously if that pairing occurs properly, then the ribosome knows it has got the right transfer RNA and will attach it to the growing polypeptide chain. The peptide bond formation occurs in the large subunit because that's where the 23S ribosomal RNA is. The 23S ribosomal RNA is that ribozyme that catalyzes the formation of peptide bonds and of course peptide bonds are what hold the individual amino acids to each other. We can also see coming off the top of the large subunit here, the newly formed polypeptide and it's coming out one amino acid at a time as the protein is being synthesized. Finally when the transfer RNA has dropped off its amino acid for the purpose of synthesis, it exits going out that E site that I described to you earlier. The process of termination is actually fairly simple. During the elongation process the ribosome is moving five prime to three prime, one codon at a time. However when a stop codon gets in the place where an amino acid would be, there is no transfer RNA that has a sequence that's complementary to any of the stop codons. It will not pair with UAA, UAG or UGA. So when this happens the ribosome simply stops and that stopping is a cue to release everything. One of the things that gets released is the polypeptide that has been synthesized to it, now goes out and away and the ribosome comes apart so that it can go begin another synthesis. With this we've concluded what I wanted to talk about with respect to the central dogma, the replication of DNA, the synthesis of RNA and the translation of protein. I hope this is helpful to you in your studies

    About the Lecture

    The lecture Translation – DNA, RNA and the Genetic Code by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. It makes peptide bonds
    2. It makes phosphodiester bonds
    3. It involves synthesis of RNA from DNA
    4. It uses RNA polymerase
    1. 23S rRNA
    2. 5S rRNA
    3. 16S rRNA
    4. 18S rRNA
    5. 5.8S rRNA

    Author of lecture Translation – DNA, RNA and the Genetic Code

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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