Translation – DNA, RNA and the Genetic Code

by Kevin Ahern, PhD

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    00:00 The process of translation occurs in three phases.

    00:03 The first phase of initiation involves the assembly of the ribosome.

    00:07 In this phase, the messenger RNA with its AUG is placed such as the AUG is located properly in a special site of the ribosome known as the P-site.

    00:18 In the process of the elongation, the ribosome moves down the messenger RNA one codon at a time reading the genetic code, and then, placing the appropriate amino acid in a covalent linkage with each subsequent amino acid.

    00:33 Now, that linkage is known as a peptide bond.

    00:36 This process occurs 5-prime to 3-primes starting at the -- near the 5-prime and of the messenger RNA and moving into 3-prime direction.

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

    00:55 Now, these figures, schematically shows ribosomes and I wanna step you through the process in terms of doing this.

    01:03 We'll focus pretty much on the elongation phase because the assembly is a little bit complicated.

    01:08 This shows the large ribosomal subunit in light green on the top and the small ribosomal subunit in dark green on the bottom.

    01:15 Spanning through and 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.

    01:25 Also, in the large subunit above, you can see some transfer RNAs that are coming in carrying individual amino acid.

    01:33 There's the messenger RNA shown in yellow that I described and here are the transfer RNAs that are coming into the large subunit as you can see.

    01:42 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 that is called the P-site.

    01:57 The third site is there is the place where the transfer RNA exits and that's known as the E-site.

    02:04 We see amino acids that are attached to the individual transfer RNAs.

    02:09 The transfer RNAs are bringing them to the point of translation.

    02:14 We see the entry of the tRNA going into the ribosome and this is actually travelling in this figure down into the ribosome, we can see that the transfer RNA anticodon is pairing based pairs with the codon of the messenger RNA, and as I noted previously if that pairing occurs properly then the ribosome knows its got the right transfer RNA and will attach it to the growing polypeptide chain.

    02:41 The peptide bond formation occurs in the large subunit because that's where the 23S ribosomal RNA is.

    02:48 The 23S ribosomal RNA, is that ribozyme that catalysis the formation of peptide bond and of course peptide bonds are what hold the individual amino acids to each other.

    02:58 We can also see coming up the top of the large subunit here.

    03:01 The newly formed polypeptide and it's coming out one amino acid at a time as the protein is being synthesized.

    03:09 Finally, when the transfer RNA has dropped off its amino acid for the purpose synthesis.

    03:17 It exits going out that E-site that I describe to you earlier.

    03:21 The process of termination is actually fairly simple.

    03:25 During the elongation process the ribosome is moving 5-prime to 3-prime one codon at a time.

    03:31 However, when a STOP codon gets in a place where amino acid would be, there is no transfer RNA that has a sequence that's complimentary to any of the stop codons, will not pair with UAA, UAG or UGA.

    03:48 When this happens, the ribosome simply stops and that stopping is a cue to release everything.

    03:54 One of the things that gets released is the polypeptide that's been synthesized with now goes out in a way and the ribosome comes apart so that it can go begin another synthesis.

    04:04 With these, 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 approaching.

    04:16 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 forms peptide bonds.
    2. It forms phosphodiester bonds.
    3. It involves the synthesis of RNA from DNA.
    4. It uses RNA polymerase.
    5. It occurs in the nucleus of the cell.
    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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    By Joseph A. on 08. September 2020 for Translation – DNA, RNA and the Genetic Code

    Good explanation. Pretty bad diagram. Animation probably would work better.

    like it but it seems that the PhD is so fast but I used the subtitles.
    By Hussein A. on 13. March 2019 for Translation – DNA, RNA and the Genetic Code

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