Biology: Separation of Proteins

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Biology: Separation of Proteins

Lab Report 1: Separation of Proteins

Abstract/Summary: “Proteins account for more than 50% of the dry weight of most cells, and they are instrumental in almost everything organisms do” (Campbell, 1999). The significance of proteins to the continuation of our biological systems is undeniable, and a study of how to quantify proteins seems an appropriate introduction to our studies of biology. In order to study proteins we must first know how to separate then quantify the amount using basic principles of experimental design such as a standard curve. In this experiment we wish to quantify the amount of previously extracted protein by measuring the absorbance of the unknown amount and determining its concentration by overlaying it against a standard curve of the absorbance of known concentrations of the protein. We used the dye agent Bradford Protein Assay to get an absorbance of 0.078, 0.143, 0.393, 0.473, and 0.527 at the protein’s respective concentrations of 0.28, 0.56, 0.84, 1.12, and 1.40 mg/mL. When a best-fit line was applied to the standard curve, and the absorbance of our unknown concentration (0.317 A) plotted, we estimated a concentration of around 0.84 mg/mL of protein. Our calculations indicated a quantity of 168 mg of protein, which was an approximately 8.96% yield of the projected 1875 mg that was expected. Errors that may have led to this small yield percentage may have stemmed from our previous lab and our initial attempts to extract the desired amount of protein.

Introduction: Within this experiment we wish to facilitate a greater understanding of the concepts of experimental design and quantifying techniques. Specifically, this lab will allow us to gain an enhanced understanding of the isolation of a protein using differential solubility, which allows us to separate and purify various proteins using high concentrations of a specific salt so that they may be studied in great detail. Last week we separated our desired protein using ammonium sulfate. Since we have already extracted the desired protein, we will begin quantifying the amount using the Bradford Protein Assay. Because it is a dye-binding assay, we will use the spectrophotometer to measure the absorbance of various dilutions of a protein: this will comprise our standard curve. We will then compare the absorbance of our extracted protein from l...

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...at keep organisms alive. “Proteins are the most structurally sophisticated molecules known” (Campbell, 1999) which is reason enough to study them. The techniques we learned in this lab form a basis from which a detailed study of proteins is possible. Following our procedure we were successfully able to set up a quantifying assay to determine the amount of protein within a milk sample, although our yield percentage was rather low. However, errors in this lab (in the form of a low yield percentage) may have an origin from our last lab. In the process of extracting proteins from the milk sample, we may have inadvertently lost some of the protein through erroneous measurements, or perhaps through poor handling of either ammonium sulfate or the dialysis tubing. While not sufficient enough (at this point) to invalidate our results, they do explain the major difference between the expected and the actual amount of protein extracted.

References:

Laboratory Manual: Biological Sciences 112, University of California Department of Biological Sciences, Fall 2001.

Campbell, N. A., Reece, J. B., & Mitchell, L. G. Biology: Fifth Edition. Addison Wesley

Longman, Inc. Menlo Park, 1999.

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