LLLCTRUPHORESIS Human blood is a complex liquid tissue consisting of cells of di

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LLLCTRUPHORESIS Human blood is a complex liquid tissue consisting of cells of different types matrix called the plasma. One type of blood cell is the erythrocyte (red tions in transporting oxygen to the body's cells. The red pigment hemoglo the specific carrier of oxygen. Hemoglobin is a complex iron-porphyrin-protein m suspended in a liquid in the erythrocyte is molecule: Normal is composed of four polypeptide chains, two identical alpha chains each residues and two identical beta chains each consisting of 146 amino gene (on chromosome 16) determines the amino acid sequence in the alpha chain, consisting of 141 amino acid acids. One whereas a diff HbA, may be symbolized as of , which indicates that it consists of two alpha (a) and two beta (B) chains of the normal adult (A) type. A minor form of adult hemoglobin, hemoglobin Az (HbAz), consists of two alpha and two delta chains, whereas fetal hemoglobin CHbE) consists of two alpha and two gamma chains. Delta and gamma are different polypeptides that substitute for beta in these hemoglobins Gene mutations are known that modify the amino acid sequence of both the alpha and the beta chains of hemoglobin. Certainly the best known of these is sickle hemoglobin (Hbs-a1 ), which is due to an alteration in the DNA that codes for the beta chain. As a consequence the glutamic acid (a charged amino acid) normally found in the sixth position in the beta chain of HbA is replaced by valine (an uncharged amino acid). Individuals homozygous for the sickle-cell gene (HoHbs) (McKusick no. 141900, variant .0243; see also no. 603903) have a serious disease that is likely to reduce their life expectancy, heterozygotes (Hi/Hb) are essentially symptom free, with a normal life expectancy. The alteration in hemoglobin structure produced by the Her gene reduces the oxygen-carrying capacity of the hemoglobin molecule and causes the erythrocyte to assume a crescent or sickle shape upon giving up oaxygen. Such sickled cells are rigid and incapable of passing through tiny capillaries, which then become blocked, thereby depriving body parts of their required blood (oxygen) supply. A painful crisis can result of that alteration, A reliable means of identifying heterozygous carriers of the H allele would be useful in counseling those individuals of their potential for producing offspring having sickle-cell anemia. Because changes in amino acid content can alter the electrical charge on the polypeptide of which the amino acid is a part, such changes can be detected by the process of electrophoresis. This, indeed, is the case for sickle hemoglobin and for other mutant forms of the hemoglobin molecule (e.g, HbC, which produces a milder form of anemia called hemoglobin C disease, McKusick no 141900, variant.0038). Electrophoresis can be used to separate a mixture of charged molecules in an electrical field. Substances to be separated must bear a net negative or net positive charge, so that they will migrate in a liquid serving as a medium for conducting an electrical current. The mobility of a molecule in electrophoresis will be determined by C1) the voltage applied, (2) the charge on the molecule, and 3) the molecular friction of the molecules involved. Speculate on the following questions and suggest possible answers to them. 1. Would the rate of movement be expected to increase or decrease as the applied voltage is

Explanation / Answer

with increase in applied voltage during electrophoresis will increase the rate of movement of the charged particle because rate of seperation is directly proportional to the applied voltage.

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