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Comparing Normal and Cancerous Tissue – Genomics

by Georgina Cornwall, PhD
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    00:01 So this is how it works. We have our chip with lots of little pieces of DNA sticking up out of it. They are probes for DNA. We have a control sample and an experimental sample. Let us say we were looking at skin cancer on the arm again and there are cells that are normal cells. We will use those as a control and then there are cells from within the cancer cells. We take those samples of cells and culture them. And when they are cultured, we can extract the messenger RNA from those cells. We call that a gene that is being actually expressed is going to be transcribed and translated. We end up with messenger RNA from the transcription process. Taking the messenger RNA says, "Yes, we are indeed expressing that gene presently at this moment." So that mRNA has extracted and we use reverse transcription to make DNA copies, but we are using fluorescent labelling so that each of those DNA copies becomes fluorescently labelled. In this case, we are using green and we are using red. We are using green for the control situation and we are using red for the cancerous cells. And we are going to compare which genes are being expressed in the normal cell with which genes are being expressed in the cancerous cell to identify what sort of mutation is happening. Where the mutation for this condition is? Here we have a mixture now of the red and the green and we are going to float this all over a biochip or DNA microarray and that microarray chip will have certain spots that glow on it because we have identified or labelled DNA that is being expressed in the cell and it is going to hybridize with those little strands that are sticking up off the chip that are probes. There are probes for the whole genome and we end up looking at an image like this. The computer analyzes which spots are glowing, which spots are not. In this case, the green spots are spots that we see expressed in the normal cells. We can identify these are genes that are presently being expressed in the normal cell and then we could look at the red spots and see these are genes that are only being expressed in the cancerous cells. And finally the yellow ones are genes that are being expressed in both. Red only being expressed in the cancerous cells, green only being expressed by the noncancerous cells and yellow being expressed by both. Let us take a moment to think which ones are you really interested in looking at? If we are trying to discern, what is going on differently in the cancerous cells than the normal cells? In gene expression, which color sequences are we looking for? We are looking for the red ones right. We are identifying that the red ones, the cancerous cells are expressing this gene whereas the noncancerous cells are not. That is the DNA or that is the gene that is perhaps associated with or the sequence of genes because there is a number of them you can see on this microarray. That is the sequence that we are interested in the difference between the cancerous cells and the noncancerous cells. We can establish gene function and its actual expression using these microarray chips. Really really cool technology. Super exciting stuff going on right now in the field of genomics.

    03:56 I hope you find this material as interesting as I do. By now you should be able to discuss why a larger genome doesn't necessarily mean more complexity as well as characterize the variety of DNA types that we find throughout the genome and recognize the importance of transposable elements in perhaps modulating gene expression as well as explain why single nucleotide polymorphisms are useful in genetic analysis. Thank you so much for listening.


    About the Lecture

    The lecture Comparing Normal and Cancerous Tissue – Genomics by Georgina Cornwall, PhD is from the course Genomics.


    Included Quiz Questions

    1. Utilize EST's to identify genes that are presently being expressed in a cell
    2. Can be used to identify expression of multiple forms of cancers
    3. Can be used to identify if any cell contains a cancer causing gene
    1. The green spots and red spots indicate the expression healthy and cancer-related genes respectively; whereas the yellow spots indicate the expression of the gene in both samples.
    2. The red spots and green spots indicate the expression healthy and cancer-related genes respectively; whereas the yellow spots indicate the expression of the gene in both samples.
    3. The green spots and red spots indicate the expression healthy and cancer-related genes respectively; whereas the purple spots indicate the expression of the gene in both samples.
    4. The yellow spots and red spots indicate the expression healthy and cancer-related genes respectively; whereas the green spots indicate the expression of the gene in both samples.
    5. The green spots and yellow spots indicate the expression healthy and cancer-related genes respectively; whereas the red spots indicate the expression of the gene in both samples.

    Author of lecture Comparing Normal and Cancerous Tissue – Genomics

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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