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Determination of isoelectric point of protein (casein).

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Determination of isoelectric point of protein (casein). Introduction: Casein is a globular colloidal protein. Globular proteins are hydrophobic proteins which in certain external condition are soluble in eater. The ph at which the protein is electrically neutral is known as the isoelectric point. A globular protein such as a casein becomes increasingly insoluble as it approaches its isoelectric point. Objectives The object of this experiment is to determine the isoelectric point of casein (protein), which can be precipitated from the solution. Apparatus 9 test tubes pipettes - 1ml - 5ml - 10ml colorimeter Materials Distilled water Acetic acid - 0.01 M - 0.1M - 1.0 M casein - 0.5g/1 in 0.1 M sodium acetate Method 1. The calorimeter is switched ON to allow it to "warm up". 2. In order to distinguish between the different acidity levels contained in each test tube, the 9 test tubes were labelled from 1-9. This is important because all solution are a similar colour. 3. Following the designated volumes required on table 1, the volumes of distilled water was then pipetted into each test tube. The acetic acid was then pipetted into each test tube according to the values in the table 1. 4. In order to reduce the chances of contamination , the designated amounts of 0.01M acetic acid was pipetted first to test tubes 1 and 2 because the 0.01 M acetic acid is the least concentrated acid of the 3 acids. ...read more.


Its structure is composed of amino acids held together by electrostatic bonds. Amino acids are amphoteric. The molecular inherent structure of amino acids uniquely determines it chemical properties. Amino acids are composed of an amino group, NH2, which is basic, and a carboxyl group, COOH, which is acidic. The basic group tends to accept hydrogen ions from the acidic group. The acidic group tends to donate hydrogen ions to the basic group. The specific structure of the functional groups, directly affect the behaviour of the amino acids. The chemical behaviour of amino acid will change relatively, according to changes in the functions of state. According to the results, value for turbidity continuously increased form zero to 0.4 as pH continuously from 3.5 to 4.7. The value for turbidity reached its maximum at pH 4.7. Beyond pH 4.7. the value of turbidity continued to decrease to zero. The maximum value of turbidity was 0.4, which occurred in the solution of pH 4.7, where the hydrogen ion concentration is equal. This value corresponds to the position of the isoelectric point of the amino acid, because the level of turbidity began to decrease in the examples of casein that are exposed to pH levels greater than pH 4.7. The isoelectric point corresponds to the position of the energy level at which , the amino acid becomes dipolar, where its overall electrostatic charge is neutral, when the ...read more.


experiment during the pipette stage where relatively low volumes (fractions of 1ml, for example, in the case of test tube 1 where 0.62 mls) of acetic acid were added to the distilled water were probably not dispensed accurately enough. Since the operating threshold of biological molecules is relatively fine, the finest of differences causes substantially greater differences in the readings for the levels of turbidity in the solutions. For example, the mouth of the 1ml pipette gauge did not fit tightly into the dispenser which continuously caused air bubbles to enter the solution, which would affect the actual volume of solution dispensed into the test tubes, particularly wherever the volume required was less than 1 ml. Tube Number 1 2 3 4 5 6 7 8 9 Mls. Distilled water 8.38 7.75 8.75 8.5 8 7 5 1 7.4 Mls. 0.01 M acetic acid 0.62 1.25 0 0 0 0 0 0 0 Mls. 0.1 acetic acid 0 0 0.25 0.5 1 2 4 8 0 Mls. 1.0 acetic acid 0 0 0 0 0 0 0 0 1.6 Ph 5.9 5.6 5.3 5.0 4.7 4.4 4.1 3.8 3.5 Turbidity (0 - 3+) 0 0 1+ 2+ 3+ 2+ 2+ 0 0 Tube Number 1 2 3 4 5 6 7 8 9 PH 5.9 5.6 5.3 5.0 4.7 4.4 4.1 3.8 3.5 Turbidity 0 0 0.1 0.3 0.4 0.3 0.2 0.1 0 ...read more.

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