Extended Experimental investigation
Factors Affecting Enzyme Action
This lab will be driven by the research question, which pH level has the most successful effect on the activity of the enzyme Pepsin (protease) in the breakdown of the substrate, albumin.
Pearson Baccalaureate: Standard Level Biology Developed Specifically for the IB Diploma describes enzymes as “protein molecules which act as catalysts for reactions. As catalysts, the real function of enzymes is to lower the activation energy of the reactions that they catalyze” (Ward, Tosto, McGonegal, & Damon, 2007). Enzymes are globular proteins that have an overall 3D structure. (George, 2014).
Glands in the mucous membrane of the stomach make and store an inactive protein called pepsinogen. Pepsin is secreted as an inactive form as it is a protein-digesting enzyme and this prevents the gastric gland being destroyed by its own enzyme through auto digestion (Roberts, Reiss, & Monger, 2000).
This inactive protein is kept in its zymogen (inactive) form until it is secreted into the gastric liquids of the stomach, where it is exposed and activated by the hydrochloric acid, and also by pepsin itself as a autocatalytic reaction (Ward, Tosto, McGonegal, & Damon, 2007). Once secreted, the mucus lining inside of the stomach prevents the functioning enzyme from attacking the cells (Roberts, Reiss, & Monger, 2000).
When food is digested, the food is forced down to the stomach by consecutive series of smooth muscle contractions called peristalsis. Once the food is in the stomach, it is held for a period of time in order to mix with the gastric juice (Cleveland Clinic , 2013). Gastric juice is a moist secretion containing hydroc...
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...tly. The enzyme and substrate form a reaction intermediate, and the reaction requires a less amount of activation energy when compared to the reaction between reactions without a catalyst present. (Royal Society of Chemistry, 2004).
The optimum pH of pepsin is 2.0 due to the lock and key theory and the collision theory that is most effectively reactive whilst in this very acidic environment.
This provides the necessary pH that sustains the shape or the properties in its most convenient state so that so that the reaction can be undertaken successfully in a shorter amount of time. Therefore, if the pepsin is placed in various pH environments of 0.5, 1, 1.5 and 2 molar HCL and the substrate, albumin is added to each test tube of pepsin, then the pepsin placed in 2.0 molar HCL will produce the maximum amount of enzyme activity, as it is the optimum pH of pepsin.
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