Mutations in General

by Georgina Cornwall, PhD

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    00:01 Sometimes though things go a little bit arise. What when all these mechanisms are bypassed and we actually end up with a mutation in a cell that is going to become a gamete and that mutation gets passed on. Let us look at some point mutations and following that we will look at chromosomal mutations. Point mutations involve one change or a very small change in the local area on a strand of DNA or in the chromosome whereas chromosomal mutations are large scale changes in the structure of chromosome. Our point mutations will visit our friend, here again, hemoglobin. Previously I have introduced you to sickle cell anemia and its relationship to hemoglobin. You recall hemoglobin has two alpha subunits and two beta subunits that each has a slightly unique folding pattern and create an active site for the binding of oxygen. If the binding site is messed up, it is not going to carry oxygen or it is not going to fold in a proper way to allow it to do its job properly. Let us look at what has gone on specifically. This sickle cell anemia results from a point mutation, one nucleotide base change. Here is our normal hemoglobin B gene and what it results in coding in our amino acid sequence and then when we have abnormal hemoglobin, we can see a slight change, which results in a changed amino acid. Here is the change.

    01:43 We are just changing and A for a T, very, very small change with a very profound effect.

    01:50 We are changing from a polar amino acid to a nonpolar or hydrophobic amino acid and that presents some problems in protein foldings such that the beta chains will have a different folding arrangement so that they are very sticky and don't stack up quite properly in the red blood cells. So they will start to form chains where the deoxygenated portion of the beta subunit will fold in a little bit and that will cause them to stick together in these chains and when they end up inside the red blood cell in this form, the oxygenated form then they cause the cell to sickle. They are okay when they are oxygenated, but hemoglobin has to be oxygenated and deoxygenated. This is why we only see the profound effects of sickle cell anemia in lower oxygen environments or during hard exercise because when there is a lack of oxygen, it is less oxygenated sickles and the cells will get stuck at places and causes a platter of different effects. That is an example of how a single point mutation can have such a vast effect on gene expression and the shape of final proteins.

    About the Lecture

    The lecture Mutations in General by Georgina Cornwall, PhD is from the course DNA Repair & Genetic Mutations.

    Included Quiz Questions

    1. Sickle-cell anemia
    2. Down Syndrome
    3. Cri-du-Chat syndrome
    4. Williams syndrome
    5. Tay-Sachs disease
    1. …leads to an abnormal deoxygenated hemoglobin tetramer chain formation that will cause the cell to sickle.
    2. …is a gene defect caused by a point mutation of a single nucleotide of the β-globin gene.
    3. …results from the substitution of glutamic acid by valine in the β-globin chain.
    4. …leads to a sudden rise in the oxygen-carrying capacities of the RBCs and WBCs in humans.
    5. …leads to an abnormality in the structures of the immunoglobin proteins during cancer.

    Author of lecture Mutations in General

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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