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Protein Digestion Design Lab. To detect the amount of protein molecules or short polypeptide chains in the cooked egg white for this experiment, the biuret reagent will be used.

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Protein Digestion Design Lab Introduction It is known that the chemical digestion of protein occurs in the stomach and small intestine. Proteins are polymers of monomers known as amino acids (a monomer is one unit of amino acid) aligned in a genetically determined sequence. Proteins contains the elements carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur. The amino acids in a polymer are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism. An enzyme is a biological catalyst made up of protein. It alters the rate of a chemical reaction without itself being chemically changed at the end of the reaction. Variables that affect enzyme activity include temperature and pH. There is a particular optimum temperature and pH which allow enzymes to perform most efficiently. This implies that since the structure of the enzyme can be affected by temperature and pH, enzymes must be proteins. When the bonds which give a protein its unique shape are broken, the protein, in this case an enzyme, is denatured. ...read more.


Incubator 12. Electronic scale 13. 10 ml granulated cylinders 14. Stir rods 15. Scoopulas 16. Eye droppers 17. Scalpels, 18. Biuret reagent 19. Hot plates 20. Distilled water Method 1. Wash all the test tubes thoroughly 2. Cut the egg white into 8 equal pieces of 3-5mm in length 3. Put each piece of egg white into each of the 9 test tubes, number the test tubes A through B. 4. Test the egg white samples in the test tubes by adding the following substances: Test tube A - 5ml of distilled water Test tube B - 5ml of distilled water and 1ml of 0.01M sodium hydroxide Test tube C - 5ml of distilled water and 1ml of 0.01M hydrochloric acid Test tube D - 5ml of pepsin solution Test tube E - 5ml of pepsin solution and 1ml of 0.01M sodium hydroxide Test tube F - 5ml of pepsin solution and 1ml of 0.01M hydrochloric acid Test tube G - 5ml of pancreatin solution Test tube H - 5ml of pancreatin solution and 1ml of 0.01M sodium hydroxide Test tube I - 5ml of pancreatin solution and 1ml of 0.01M hydrochloric acid 5. Test the pH level of the solutions in all of the test tubes. Record this. 6. Set the test tubes for 24hrs in the incubator with the temperature set to 37oC. 7. Add the biuret reagent to each of the test tube mixtures one drop at a time, shaking the mixtures gently in between each drop. ...read more.


Test tube D contained only the pepsin solution, and without the acidic environment to activate the enzymes, hence no protein digestion took place. Test tube E contained the pepsin solution and the 0.01M sodium hydroxide, and the alkaline mixture prevent the enzymes from being activated to digest the proteins, so no protein digestion took place either. Test tubes G and I also did not show any results of protein digestion, as they did not contain the required chemicals to create an optimum environment for the enzyme trypsin in the small intestine. Test tube G contained only the pancreatin solution, and the enzymes would not be able to digest the proteins in a non-alkaline environment. Test tube I contained the pancreatin solution and the 0.1M hydrochloric acid, and the acidic environment prevented the enzymes from being activated to digest the proteins, so there was no protein digestion here too. In conclusion, the optimal conditions for protein digestion in the stomach would be an acidic environment of pH 2; the optimal conditions for protein digestion in the small intestine would be an alkaline environment of pH 8. Limitations of the experiment: 1. Only 1 of each trial was done 2. The experiment was based on largely quantitative results, such as based on observation of the egg white to see how much was digested, or the colour change of the biuret reagent(which can be unclear if too much reagent is added) ...read more.

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