What effect does the pH have on the enzyme diastase? What effect does the temperature have on the activity of the enzyme diastase?

Observations:

Table One:

Table Two:

1. Table One shows that the darkest colors have been obtained at temperatures of 10oC, 20oC and 70oC. As it follows, the first two temperatures show that they are too low for the enzyme to function in. The following tests were done every minute, until no further change was noticed. However, the temperature of 37oC showed the lightest color, which, furthermore, shows that it is the optimum temperature for the diastase enzyme. In this case, the diastase enzyme catalyzed the starch. At 10oC the color is dark, indicating that the enzyme did not work at all; at 20oC the color is slightly lighter, showing that the diastase worked a bit better while at 70oC the dark color shows the enzyme did not work at all.

2. Table Two contains orange colors and dark yellow colors in the pH ranges of 1 to 3, which indicates that the diastase enzyme did not function properly; therefore it did not catalyze the starch completely. The two pHs were too acidic. The pH of 7 shows the lightest yellow color, which means that the starch was completely catalyzed by the diastase enzyme. The yellow color also indicates the color of the iodine solution. The pH of 10 showed a consistent dark color, which means that the environment was too alkaline for the enzyme to work in. In this case, the starch was not catalyzed at all.

Conclusion:

• The optimum pH for the diastase enzyme is 7. The pHs of 1 and 3 are too acidic, while the pH of 10 is too alkaline. Ranking (best to worst): pH7, pH3, pH1 and pH10
• The optimum temperature for the diastase enzyme is 37oC. The temperatures of 10oC and 20oC are too low, while the temperature of 70oC is too high. Ranking (best to worst): 37oC, 20oC, 10oC and 70oC.

Discussion:

1. Enzymes are protein catalysts. They consist of a long chain of amino acids that are held together by peptide bonds. Enzymes take part in breaking down the food materials into simpler compounds and speeding up chemical processed, which would otherwise run very slowly. It does so by reducing the energy of activation, speeding it forward and reversing reactions equally. Also, after catalyzing a reaction, enzymes are regenerated intact and ready to catalyze the same reaction again. When catalyzing a reaction, chemical change takes place when the bonds between reactant molecules break and a new arrangement of atoms creates bonds between the atoms of product molecules. For this to occur, reactant molecules must collide with enough force for the breakage to occur. Main function here is to catalyze a substrate in a chemical reaction. The substrate binds to a particular site on the enzyme to which is attracted, called active site. The substrate and the active site must posses compatible shapes for binding to occur. As the substrate enters the active site, its functional groups come close to the functional groups of a number of amino acids. It is the interactions between these chemical groups that cause to change its shape. Upon completion of the reaction, products depart from the active site and enzyme is then free to bind to another substrate molecule with the same.

2. A pH of nine would most closely simulate conditions in the intestine. The pancreas secretes digestive enzymes and sodium bicarbonate to neutralize the stomach acids and establish a pH of 8.2-9, which will not only neutralize the enzyme pepsin but activate pancreatic enzymes. The absorption process occurs in the small intestine. Food has been broken down into particles small enough to pass into the small intestine. Sugars and amino acids go into the bloodstream. Glycerol and fatty acids go into the lymphatic system. The upper part is called duodenum and is the most active in digestion. It is here that the pancreas and liver secrete the enzymes that are active in a pH range of 8-9.

 

3. The gastric juice is found in the stomach and has a pH of 2. Gastric juice is released in response to the presence of food in the buccal cavity. As the stimulation by the nervous system wears off, the presence of food makes the cells in the stomach lining to produce gastrin. Gastrin passes into the bloodstream and stimulates the release of gastric juices for several hours. The gastric juices contain chief cells, which secrete pepsinogen, which is converted to its active enzyme by hydrochloric acid and pepsin itself. The first form of the pepsin enzyme prevents it from digesting the cell cytoplasm contents. The gastric juices also contain oxyntic cells which produce hydrochloric acid. The hydrochloric acid converts pepsinogen to its active form, provides an optimum pH for it to work in and kills bacteria. In conclusion, pepsin is an enzyme which catalyses the hydrolysis of proteins to polypeptides and it is best active in a pH of 2.

4. Changes in the pH can produce changes in the protein structure. Various pHs disrupt the hydrogen bonds, ionic bonds, disulfide bridges an hydrophobic interactions that hold an enzyme in the tertiary structure. If the pH range breaks the peptide bond, the shape of the enzyme is changed and cannot function anymore. Since an enzyme is a protein, it contains a COOH terminus and a NH2 terminus. When at high pH, the predominant forms will be COO- and NH2, while at a low pH the forms will be COOH and NH3.  Changing the pH also alters the properties of these salt bridges. Even a small shift away from optimum pH might mean one of these salt bridges is affected and therefore the shape and activity and stability of the protein will be affected.

5. Enzyme function is dependent on the specific configuration of the enzyme molecule which is mainly maintained by relatively weak bonding such as ionic, hydrophobic and hydrogen bonds. Heating the molecule above the optimal temperature will disrupt the weak bonding, leading to a loss of the natural configuration of the molecule.

6. Enzymes that are found in the human body act their best when the body temperature is between 37oC and 40oC. Due to the fact that an enzyme is a protein, its three-dimensional shape changes if the hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions that hold the polypeptide together in the tertiary structure, are broken by a medium with a higher temperature than the optimum. Once the enzyme changes, the active site loses its shape as well, and this way the substrate cannot bind with the enzyme anymore. Now that the enzyme cannot bind to the substrate, the chemical reaction is not preceded faster. As well, without enzymes, large molecules are not broken down (catalyzed) anymore. This is why it is important that the temperature of the body does not exceed 40oC.

7. Mammals and birds are warm-blooded organism. The advantages of homeostasis are that the organism can adjust to changes, for example in temperature and water availability, without the component cells being affected since they are having all their needs met by the internal environment. That is why some animals are able to exist at very cold surroundings like that South Pole and very hot environments like the deserts; it is due to the capability of controlling temperature. The internal environment makes it possible for the cells to work on certain tasks. For example, some cells work to maintain the optimum level of oxygen and carbon dioxide in the lungs. On the other hand, the cold-blooded animals take on the temperature of the surroundings. The only advantage here is that the chemical reactions are fast at a warm temperature, but once at a low surrounding, the rate of the chemical reaction slows down.