Factors that affect Enzyme activity

I am going to investigate a factor that affects the rate of enzyme activity What are enzymes and how do they work?

Enzymes are biological catalysts - catalysts are substances that increase the rate of chemical reactions without being used up. Enzymes are also proteins and thus have a specific shape. They are therefore specific in the reactions that they catalyse - one enzyme will react with molecules of one substrate. The site of the reaction occurs in an area on the surface of the protein called the active site. Since the active site for all molecules of one enzyme will be made up of the same arrangement of amino acids, it has a highly specific shape. Generally, there is only one active site on each enzyme molecule and only one type of substrate molecule will fit into it. This specificity leads to the lock and key hypothesis.

a) Large globular protein enzyme;

b) Active Site where the substrate combines to the enzyme;

c) Substrate which fits the active site;

d) Activated complex. The substrate is weakened to allow the reaction;

e) Unchanged enzyme/ re-used at low concentration;

f) Product of the reaction In my investigation, I will be using the enzyme catalase, which is found in most living organisms. It catalyses the decomposition of hydrogen peroxide into water and oxygen. 2H2O2 + Catalase > 2H2O + O2.

Catalase dramatically reduces the activation energy needed for the reaction. Without catalase the decomposition would take much longer, and would not be fast enough to sustain human life. Hydrogen peroxide is also a dangerous, very potent by-product of metabolism, so it is essential that it is broken down quickly, otherwise it would cause damage to cells.

The activity of an enzyme is affected by its environmental conditions. Changing these will alter the rate of reaction caused by the enzyme. In nature, organisms adjust the conditions of their enzymes to produce an optimum rate of reaction, where necessary, or they may have enzymes which are adapted to function well in extreme conditions where they live.

Enzyme Concentration: at low enzyme concentration there is great competition for the active sites and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate, for more enzymes will be colliding with substrate molecules. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor. Inquiring upon this factor, it is obvious to anticipate increasing enzyme concentration will also increase rate of reaction based upon contextual knowledge and after casting a certain amount of enzyme concentration, it will no longer be the limiting factor. If I experiment on this factor, I would perceive my data to resemble the graph below, as it exemplifies how increasing enzyme concentration increases rate of reaction(shown through line climbing) until it becomes the limiting factor and the rate of reaction does not increase(shown through line not climbing).

Substrate Concentration: similar to the enzyme concentration, at low concentrations of substrate there is a low rate of reaction. This is because there are few substrate molecules to react with active sites and therefore limiting the number of reactions happening. Henceforth, increasing the substrate concentration will increase the rate of reaction. This is because more substrate molecules will be colliding with enzyme molecules, so more product will be formed. However, after a certain concentration, any increase will have no effect on the rate of reaction, since Substrate Concentration will no longer be the limiting factor. The enzymes will effectively become saturated, and will be working at their maximum possible rate. If I was to investigate this factor, I would predict the rate of reaction will increase as substrate concentration increases, until a certain concentration is added when the substrate molecules are in excess resulting in enzyme saturation. The graph (below) demonstrates my prediction.

Simple image portraying proposed image for enzyme and substrate concentration (discussed in according factors). Mentioned as “picture of proposed investigation below”. Temperature: All enzymes have optimal temperatures, the temperature at which an enzyme produces the highest reaction rate for a specific reaction. The majority of enzymes in the human body works best at 37 Celsius degrees. This is because 37 degrees Celsius is the body’s internal temperature and enzymes such as catalase, have been adapted to work best at that certain temperature. Below the optimum temperature, substrates have little kinetic energy and fewer enter the active site to be catalyzed. However, as temperature increases towards the optimum, the substrates and enzymes gain more kinetic energy and collide more often leading to a chemical reaction. When the temperature goes above the optimum, the bonds holding enzymes together also gain kinetic energy, increasing the speed at which they vibrate. This leads to the bonds breaking within the enzyme, making it change shape. This change in shape means that the active site is less complementary to the shape of the substrate, so that it is less likely to catalyse the reaction. Eventually, the enzyme will become denatured and will no longer function. Then as temperature increases more enzymes’ molecules’ active sites will become less complementary for the substrate molecules and then more enzymes will be denatured. This will decrease the rate of reaction. If I examined this factor, I would predict that the rate of reaction will peak at 37 degrees Celsius, as that is the optimum temperature of catalase. Also, as stated in the latter paragraph, increasing or decreasing the temperature from its optimum will lower the rate of reaction. Therefore, I should expect the data I collected to be similar of the graph below.

PH: pH measures the acidity and basicity of a solution. It is a measure of the hydrogen ion (H+) concentration, and therefore a good indicator of the hydroxide ion (OH-) concentration. It ranges from pH1 to pH14. Lower pH values mean higher H+ concentrations and lower OH- concentrations.

Unlike the same optimal temperature for all enzymes that dwell in the human body (370c); the optimum pH varies for the enzymes. For example, the enzyme pepsin has an optimum pH of 2.0 whereas catalase has an optimum of 7.6. Enzymes in different locations have different Optimum pH values since their environmental conditions may be different. In this instance, pepsin operates most competently at pH 2 because it is commonly found in the stomach, where pH is low due to the presence of hydrochloric acid. Enzymes work in small ranges of pH values, so any change above or below the optimum will cause a sudden decrease in rate of reaction, since more of the enzyme molecules will have active sites whose shapes are not (or at least are less) complementary to the shape of their substrate.

Small changes below or above the optimum, does not cause a permanent change to the enzymes since the bonds can be reformed. However, extreme changes in pH can cause enzymes to denature and permanently loose their function. When the pH is changed from the optimal of the certain enzyme, the H+ and OH- interfere with hydrogen and ionic bonds that hold together an enzyme, since they will be attracted or repelled by the charges created by the bonds. This interference causes a change in the shape of the enzyme and most importantly, the active site. If investigating this factor, I would expect the enzyme activity to decrease as the pH differs from 7.8, which is the optimum of the catalase. This is because the active site is becoming less complementary for the substrate to bind towards and eventually becomes denatured. The graph, below, supports my expectation and I would expect my data to portray the graph.

From all the possible factors that could be investigated I have decided to investigate temperature.