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Junctional Diversity, N-Nucleotide Addition and Somatic Hypermutation – Lymphocyte Development

by Peter Delves, PhD
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    So let’s look at this process of recombinatorial inaccuracy. So, as you can see on the left, we have the germline DNA, just showing you the D segment and the J segment, and showing you three codons. CCC, CCC in the D segment and then a codon TGG in the J segment. When the recombination occurs, it may be that the splice junction is taking the codon CCC and putting it next to TGG. Now CCC is the codon for the amino acid Proline, and TGG is the codon for the amino acid Tryptophan. So in this particular recombination, you’ll have a Proline and a Tryptophan next to each other in the amino acid sequence, but it doesn’t have to be. For example in another B-cell using exactlt the same D segment and exactly the same J segment, the splice junction may be slightly different. So in this example, the B-cells use that CCC codon, so still be a Proline. But because the splice point is slightly different, instead of the next codon being TGG, it’s CGG. That means that instead of having a Tryptophan, there is an Arginine amino acid at that particular position. And in the third example shown here, you can see that the second codon is CCG which again encodes the Proline. So we have CCC and CCG both encoding Proline amino acids. So you can see that by this very basic kind of technique in a way, of just slightly changing where the splice junction is, it can create additional diversity for the antibody molecule. What about N-nucleotide addition? Well, when the DNA is cut during D to J recombination, and V to D recombination in the heavy chain, and J… V to J recombination in the light chain; before the DNA is re-spliced, the...

    About the Lecture

    The lecture Junctional Diversity, N-Nucleotide Addition and Somatic Hypermutation – Lymphocyte Development by Peter Delves, PhD is from the course Adaptive Immune System. It contains the following chapters:

    • Recombinatorial Inaccuracies
    • N-Nucleotide Addition
    • Somatic Hypermutation

    Included Quiz Questions

    1. Alterations in the original blueprint for the light and heavy chains of the immunoglobulin
    2. Variety of amino acid expression
    3. Protein sequences that produce a greater diversity of antibodies
    4. Protein sequences that produce antibodies that are dysfunctional
    5. Different combinations of amino acids from the same germline DNA
    1. Inserts nucleotides into area that has been cut during recombination
    2. Splices DNA back together
    3. Determines where DNA will be cut during D to J recombination
    4. Cuts the DNA in V to D recombination
    5. Recognizing splice junction, allowing enzymes to insert additional nucleotides
    1. Increases affinity for antigens and diversity in antibodies
    2. Decreases affinity for self and increases diversity in antibodies
    3. Increases affinity for antigens and decreases affinity for self
    4. Decreases affinity for antigens and diversity in antibodies
    5. Increases affinity for antigens and decreases diversity in antibodies

    Author of lecture Junctional Diversity, N-Nucleotide Addition and Somatic Hypermutation – Lymphocyte Development

     Peter Delves, PhD

    Peter Delves, PhD


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