Coding and Noncoding DNA Sequences

by Georgina Cornwall, PhD

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    00:00 That is a great explanation, but something else still has to be going on. When we look at DNA, I can tell you that we have identified some fairly consistent patterns. There are some coding regions and there are some noncoding regions. The types of DNA that we find in coding regions are single copy genes. Those are genes that have a function and do something.

    00:24 We also can see that there are segmental duplications. In segmental duplications, for example, a whole sequence of coding genes could be copied to another chromosome. Chromosome 16 has a lot of prevalence throughout the genome. Sections of it have been copied onto, I think it's 19 different chromosomes. Their genes that have been repeated throughout the genome. And addition to that, we might see coding regions where we have multigene family. Genes that work together are located in similar locations on the chromosome or perhaps in sequence so that they can be produced together when we unravel that section of DNA. And then we could have tandem clusters. These tandem clusters are genes that need to be replicated at a high rate. It is a cluster of genes. Let us say we need a whole bunch of the same sort of protein made at one time. The gene will often be repeated so that it can be produced in a higher volume. When we are translating and transcribing that particular region, we are transcribing multiple copies at the same time because there are multiple copies of genes in a row. Those are our coding DNA sequences, but more interesting we get into these noncoding DNA sequences and we have spent quite a lot of time and research trying to characterize what is going on in these noncoding sequences that we previously called junk DNA. Well we now know that it is definitely not junk DNA. If you throw it away, things don't go very well at all. First of all, we know there are exons. I mean there are introns and exons. The exons are expressed. The introns are not expressed. So, noncoding regions, we have got introns. Then we will have structural DNA for example around the centromeres of chromosome. That DNA doesn't seem to have any function, but it stays tightly wound so that the centromeres have structure may be to attach the kinetochore handles too. The structural DNA doesn't code for stuff and there are simple sequence repeats. We have seen those when we looked at DNA fingerprinting with STRs, short tandem repeats. Simple sequence repeats, they are not coding for anything. We use them for things but what are their roles? Investigations run the way to figure these things out. We can also see that there are segmental duplications, large regions of chromosomes that are moved and copied to other regions similar to coding sections, but they are not coding sections. Why are these sections moving around which brings us to the idea of transposable element? Transposable elements are otherwise known as jumping genes. They are all over the place in the genome and they can move themselves from one place to the other and we have long wondered what the purpose of this jumping gene is. We may also see pseudogenes.

    03:40 These are genes that have perhaps become inactivated by maybe even a transposable element jumping into the middle of them or they are mutated so that they no longer have functional expression.

    03:55 We may also see noncoding sections of micro RNAs. These make little baby RNAs that are perhaps involved in gene expression as well as long non-coding RNAs.

    About the Lecture

    The lecture Coding and Noncoding DNA Sequences by Georgina Cornwall, PhD is from the course Genomics.

    Included Quiz Questions

    1. ...the identification of open reading frames.
    2. ...the alignment of contigs.
    3. ...the construction of a genetic map.
    4. ...shotgun cloning.
    1. Introns ----- A part of gene which gets expressed in the mature mRNA molecule.
    2. Pseudogene ----- A non-functional gene originated due to insertion of a transposon element or a mutation.
    3. Simple Sequence Repeats ----- Helpful in DNA fingerprinting.
    4. Centromeric DNA ----- A structural part of centromeres which helps in proper segregation and transport of chromosomes during cell division.
    5. Transposon ----- A jumping gene able to change its position within the genome
    1. Transposon
    2. Single copy gene
    3. Segmental duplication
    4. Multigene families
    5. Tandem clusters

    Author of lecture Coding and Noncoding DNA Sequences

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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