Extraction and Characterization of Proteins

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The experiment, entitled Extraction and Characterization of Proteins, aims to isolate casein from milk and albumin from egg; to explain the methods employed for protein extraction; to apply spectrophotometric methods in characterizing and quantifying extracted casein and albumin. The experiment was divided into 2 parts; the extraction of Albumin from egg and the determination of protein concentration via the Warburg-Christian method and Bradford Assay method. In the first part, egg white underwent the addition of a weak acid, disruption of cell membrane, addition of ammonium sulfate and centrifugation. The product obtained was not weighed because of its relatively small amount and was considered a failure by the experimenters. In the second part of the experiment, the protein concentration of the product acquired from the first part was calculated to be 5.1 mg/mL using the Warburg-Christian method. In the Bradford assay method, however, a negative value for the concentration was derived (-0.116) which led to the use of another solution provided by the instructor. The concentration of the new solution was determined to be 0.024 mg/mL using the Bradford assay method. The use of different solutions in the two methods accounts for the difference in protein concentration calculated. From these results, it can be concluded that the experiment failed to extract the desired amount of proteins, although it was shown that there are different relatively accurate ways in the determination of protein concentration.

Discussion Data and Results

Proteins are polymer organic molecules made up of monomers known as amino acids. First discovered in 1838, it was coined from the Greek word proteios, meaning primary—a word which describes its role in the composition of living organisms since it is the primary component of basic biological parts like the cell. Humans alone are composed of 15% proteins (Pauling et al, 1954) and have about 30,000 different kinds of proteins, of which only 2% have been adequately described (Hendrix, 2007). Proteins are composed of about 20 amino acids made up of carbon, hydrogen, nitrogen, oxygen and, sometimes, sulfur molecules. An amino acid is a short carbon skeleton with an amino group on one end and a carboxylic acid on the other. All amino acids have identical structures, all have amino groups, carboxylic acids and a hydrogen directly bonded to the alpha carbon, except for their side chains. These differences dictate the structure and the function of proteins.

Proteins are abundant in nature. In a typical human diet alone, various proteins can be detected from different food items. Such proteins include albumin, a simple protein which constitutes an important part of the diet and can be found in egg white, milk, muscle, blood plasma and plant seeds. These albumin-containing food items are great sources of protein. Aside from its importance in nutrition, it has also been used in different industries. During the Spanish colonial period in the Philippines, albumin containing materials like egg whites were used as cement in building churches and other edifices because of the ability of albumin to form mass of great hardness when mixed with slaked lime. It is also widely used in sugar refining processes because of its ability to coagulate when heated to 70oC, where it can remove cloudy precipitates and clarify solutions. Albumin is also used as an antidote for toxins like bichloride of mercury, sulfate of copper, and nitrate of silver because of its ability to form insoluble compounds with some metallic salts. Another example of a commonly used protein is casein. Casein, in its pure form is actually a group of proteins (Redmond, 2007) called phosphoprotein, a group of proteins bonded to a substance containing phosphoric acid. Its name was coined from the latin word caseus, which means cheese, because it accounts for nearly 80%of the proteins in milk and cheese. With the help of...
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