Factors Affecting Enzyme Activity Experiment

• May Zheng Lab Partners: Vena G. and Sara W.

Observations:

Part A: The Effect of Surface Area on Enzyme Activity

Table1: Amount of Foam Produced by Potato Samples with Different Sizes

Part B: The Effect of pH on Enzyme Activity

Table 2: Amount of Foam Produced in Mixture of Mashed Potato and Liquid of Different pH Levels

Part C: The Effect of Temperature on Enzyme Activity

Table 3: Amount of Foam Produced by Enzymatic Reaction at Different Temperatures

Discussion:

The rate of enzyme activity increased along with the surface area of substrate. As particle size decreased, the surface area increased. Hence in the experiment, the large lumps of potato pieces were involved in a much slower reaction compared to the mashed potatoes which had produced a larger amount of foam in one minute. With the large pieces of potatoes, the catalase enzyme were only exposed to the surface of the pieces whereas, the mashed potatoes covered a larger surface area for the enzyme to act upon resulting in greater enzymatic activity. Chemical reactions could only occur with the collisions between particles. By maximizing the surface area of the potato, there was a greater the probability of collisions between the potato particles and the catalase enzyme. The larger the number of particle collisions per second, the faster the rate of enzyme activity (Clark, 2002).

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The small intestine was a vital segment of the human digestive tract responsible for the most portion of digestion and absorption of nutrients. Hence, it had been specifically adapted to maximize the efficiency of the digestion and absorption processes. The small intestinal border consisted of multiple inner circular folds, villi and microvilli structures which contributed to its large surface area. Many enzymes were found on the surface of the intestinal brush border such as sucrose, maltase, and lactose waiting to break down disaccharides into the specific individual monosaccharide molecules. The extended surface area provided the enzymes with a larger space to work with and easy access to a greater concentration of substrate increasing the reaction rate (“How Does Disgestion,” 2013). The small intestine was divided into three sections: the duodenum, the jejunum and the ileum. Most digestion occurred in the duodenum with the presence of sodium bicarbonate produced by the hormone secretin. In the stomach, hydrochloric acid was produced to assist in breaking down the ingested food. As the acidic chyme reached the small intestine, the sodium bicarbonate played the role of a neutralizer. Considering that enzymes denatured at extreme pH levels; in order to maximize enzymatic activity in the small intestine, sodium bicarbonate was produced to raise the pH level from two to approximately seven which had created the optimal condition for enzymes to function properly (Ori, 2014).

Most enzymes were multi-proteins complexes composed of several individual protein molecules, in rare cases they could be RNA molecules such as ribozyme. Enzymes were considered to be compounds high in molecular mass. Its structure consisted of defined chains of amino acids that were held together by the means of peptide bonds forming polypeptide chains. The sequence of amino acids that made up the polypeptide chains varied for different enzymes and contributed to their distinct three – dimensional structures due to the different locations where chains were folded (“Enzyme structure and,” 2013). Furthermore, all enzymes possessed an active site where the catalysis occurred in the presence of the reacting substrates. The shape of the active site was specific to the substrates. Reaction would not occur if the substrate molecule couldn’t fit into the active site due to shape mismatch (“Enzymes,” 2005).

pH levels had a significant influence on the rate of enzymatic activity. Extreme pH values could result in the denaturation of enzymes or in order words, the complete loss of function and activity. Generally, enzymatic activity rate declined with the gradual increase and decrease of pH levels from the optimum value. The optimal pH level was the favourable value in which the enzymatic activity was at its highest or fastest rate. For example in the experiment, the reaction between mashed potato and HCl (aq) at a pH value of 4 had only produced approximately 0.5mm of foam after one min and with NaOH at a pH level of 8, only 1mm of foam was produced. In comparison, approximately 3 mm of foam was produced from the reaction between mashed potato and water with a pH level of 6.5. Hence, it could be concluded that the optimum pH level which maximized the enzymatic activity of catalase was around neutral or 7. However, different enzymes could vary significantly in optimal pH levels. For example, lipase in the stomach which broke down lipids had a pH optimum of 4.0 to 5.0, whereas trypsin had a pH optimum of 7.8 to 8.7 (“Introduction to Enzymes,” 2014).

In order for enzymes to catalyze biochemical reactions, substrates needed to bind to its active site. The active site had a very specific geometric shape that was complementary to the shape of its substrates. This suggested that enzymes could only react with certain compounds. The Lock and Key model proposed by Emil Fischer was an analogy of the interaction between an enzyme and a single substrate. In this theory, the lock represented the enzyme and the key was the substrate. The lock could only be opened by the key with the correct size, shape and pattern of its teeth. Hence, a reaction could only occur if the substrate fitted perfectly into the active site of the enzyme. Larger or smaller keys and differently shaped keys could not unlock or even fit into the lock. Similarly, substrates with different geometric structures from the enzyme could not bind to the active site resulting in no reaction (Ophardt, 2003).

However, there had been a few experimental incidences that couldn’t be explained by using rigorous lock and key theory. Thus, another theory called “induced fit” was proposed. The induced fit theory suggested that the substrate had some control in determining the ultimate shape of the enzyme due to the enzyme’s limited flexibility. The theory was used to explain how some substrates were able to bind to the active sites even though their shape did not precisely match with that of the enzyme. The theory stated that the original interaction between the enzyme and substrate might be relatively weak due to shape mismatch; however these weak interactions quickly triggered alterations in the enzyme’s structure in order to better match the shape of the substrate, strengthening the binding (Ophardt, 2003).

Temperature was a factor that affected the rate of enzymatic reactions. Generally, as temperature increased, the rate of reaction also increased. This only applied when the values are below the optimal temperature; as the temperature exceeded the optimal level, the rate of reaction will begin to decrease and eventually stop. The optimal temperature was a value in which the reaction proceeded at its highest/maximum rate; for example, enzymes in the human body were the most efficient in their functions at a temperature of ~36 Celsius. The reason behind the increase could be explained by kinetics. As temperature increased, the probability of collisions between substrate and enzyme also increased allowing them to quickly form enzyme-substrate complexes resulting in a faster rate. Also, at low temperatures enzymes were often inactive since there wasn’t enough energy to induce motion and collision between the molecules resulting in slow or even no reaction. As the temperature surpassed the optimal value, the heat increase was high enough to break the weak bonds (hydrogen bonds) that maintained the three-dimensional structure of the enzyme. The enzyme would then start to change its shape due to the extremely high temperature. The altered shape of the enzyme prevented the substrate from binding to its active site. Hence, fewer enzymes were able to function properly decreasing the rate of reaction. As temperature continued to increase, at some point all enzymes would become non-functional/ denatured causing the reactions to come to a full stop (“How temperature affects,” 2014 ).

In this experiment, at 10 Celsius the reaction between the mashed potato and hydrogen peroxide produced 11mm of foam after one min and at room temperature the reaction produced 16mm. An assumption could be made that room temperature might have been or if not closer to the optimal temperature than 10 Celsius. However, at 80 Celsius there was a significant decrease in the amount of foam produced within a minute at 3mm suggesting that the enzyme catalase was beginning to denature at that high temperature.

Cofactors and coenzymes were both non-protein substances required to assist the apoenzyme in the catalysis reaction. Several enzymes couldn’t exert their activity in the absence of these substances. Also, the two attached to the active site of enzymes and participated in the reaction however weren’t considered to be substrates. Cofactors were molecules containing inorganic ions or metal ions. An example of a holoenzyme was carbonic anhydrase which contained a zinc cofactor attached to the enzyme’s active site. Cofactors were often obtained through the consumption of minerals. Coenzymes on the other hand, were organic compounds that often acted as the in-between carriers of electrons, certain atoms or functional groups which were transferred in the complete reaction. Coenzymes were generally obtained through the consumption of vitamins. A few coenzyme examples were Flavin adenine dinucleotide (FAD) which could be obtained from vitamin B2, and carbamide coenzymes which functioned as alkyl group carriers in the course of the catalysis reaction and could be found in vitamin B12 (“Coenzymes and cofactors,” 2014 ).

Denaturation was the process of the loss of the enzyme’s function caused by a permanent alteration in the structure/shape of the active site on the enzyme. Unfavourably high temperature and extreme pH levels could all cause enzymes to denature. As enzymes denature, the folded protein chain began to unravel, buckle and twist into deformed shapes losing their ability to bind to substrates resulting in the loss of enzymatic activity/function. Once the enzyme became denatured, it can no longer return to its original shape and function even with the removal of the liable factor. In the human body, certain biological solutions such as blood acted as buffers assisting in the prevention of the denaturation of enzymes and proteins (“Enzymes,” 2014).

A competitive inhibitor was a molecule with a similar shape as the substrate that competed with the substrates for the active site on the enzyme. The competitive inhibitor prevented reactions from occurring between the substrate and enzyme by binding to the active site of the enzyme without changing the site’s shape. Non-competitive inhibitors were molecules that attached to sites on the enzymes other than the active site. Most non-competitive inhibitors were attached to the allosteric site which was the location on the enzyme that regulated the amount of products yield. Often, the build-up of products caused the substrates to become non-competitive inhibitors in order to stop or reduce the enzymatic activity. These molecules might inhibit the reactions between the substrate and enzyme by altering the shape of the active site preventing the substrate to bind to the active site due to structure incompatibility. Both types of inhibitions could be reversible. A competitive inhibition could be reversed by increasing the substrate concentration which then would “knock” the inhibitor off the active site. A non-competitive inhibitor often popped out from the allosteric site by itself as the concentration of products decreased. Irreversible competitive inhibition was when the inhibitor molecule permanently attached itself to the active site of the enzyme causing the enzyme to lose its function (“Difference between competitive,” 2012).

There were several advantages to multienzyme complexes where series of different enzymes and reactions were used to break down an organic compound. Multienzyme complex increased the efficiency of the catabolic process since the product from one reaction was the substrate required to trigger the following reaction. Furthermore, the reactions were more controlled since the substrates involved remained in the complex as they passed through the series of enzymatic reactions. The products of one reaction were channelled directly to the successive enzyme without being released from the complex. This prevented the potential substrates from diffusing away from the reaction location and it protected the intermediates from participating in unwanted side reactions (“Energy and metabolism,” 2014).

Most enzymes were selective catalysts that tended to have specific substrates which could bind to their active sites triggering specific catalysis reactions. There were four different types of enzyme specificity. Some enzymes could only catalyze one specific reaction or substrate; this was called “absolute specificity.” Group specificity was a type of specificity where enzymes only acted on similar compounds containing a specific functional group such as the amino and alkyl groups. Enzymes that exhibited linkage specificity would only catalyze molecules that have a certain chemical bond such as ether linkages. Lastly, stereochemical specificity was used to describe enzymes that only reacted with a particular optical isomer (“Specificity of enzymes,” 2014).

The significance of enzyme specificity was to prevent enzymes from participating in unnecessary reactions by limiting the types of substrate that the enzyme could catalyze. If all enzymes were able to carry out any kind of catalysis reactions, there would be large accumulations of products verses a lack of reactants. Enzyme specificity contributed to the complexity and size of the human body. By providing enzymes with the ability to only perform certain reactions, it helped the human body to function efficiently in its current structure (“Specificity of enzymes,” 2014).

Errors:

During the experiment, a few errors were made which had affected the recorded results. In part A, the three samples of potatoes with distinct sizes used in the same reaction differed slightly in their mass. This would’ve altered the results since the height of foam produced was measured after a given amount of time. The sample with a slightly higher mass would’ve produced a smaller amount of foam than the theoretical yield and the sample lower in mass would’ve had a higher actual yield than the theoretical yield. Furthermore, for all parts to the experiment the mashed potato samples used weren’t perfectly/completely crushed. This would’ve caused the rate of reaction to decrease slightly resulting in a lower actual yield of foam in the given amount of time.

Conclusion:

It was concluded that surface area, temperature and pH levels all had significant influence on the rate of enzymatic activity. As surface area of substrate increased, the rate of reaction had also increased and vice versa. All enzymes had an optimal temperature and pH level where the enzymatic activity was at its highest rate. For many enzymes the optimal temperature was around room temperature and the optimal pH level was around 7 (neutral). As the temperature rose above the optimal value, the enzymes began to denature and lose their function due to damage in structure/ shape of active site. Both extremely high and low pH levels were able to denature the enzyme. There were two types of non-protein substances that helped enzymes carry out reactions. Co-factors were inorganic ions found in minerals while co-enzymes were organic compounds found mostly in vitamins. The rate of enzymatic activity could come to a stop in the presence of competitive and non-competitive inhibitors. Competitive inhibitors attached themselves to the active site on enzyme to prevent the binding of the substrate whereas non-competitive inhibitors attached to the allosteric site often alter the shape of the active site to stop or decrease the rate of enzymatic activity. Most organic compounds were broken down by multienzyme complexes with the intention of improving the efficiency of the whole process. Lastly, the specificity of enzymes played a major role in the complexity and large size of the human body.

References

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