2014 Year 11 Biology
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 hydrochloric acid, mucus lining, and the enzyme pepsin, which breaks down proteins into short polypeptide chains. Not only does the HCL contribute to the activation of the pepsinogen, it also provides the optimum pH (the pH at which an enzyme has maximum activity). HCL is produced by oxyntic cells in the central region of the gastric glands and gives the gastric juice an acidic pH of less than 2.0 (Roberts, Reiss, & Monger, 2000).
Most enzymes have an optimum pH that falls within the range of 7.0 – 7.5 which symbolizes a neutral pH (similar to distilled water). Unlike most enzymes, pepsin has an on optimal pH of 2.0 where it exhibits maximum activity, whilst it becomes inactive at pH 6.5 or above, yet it is not completely denatured until it reaches pH 8.0. Therefore pepsin can be reactivated through...