10.1 Enzymes

Task 1 – Using a number of labelled diagrams, briefly state the process of how enzymes speed up reactions. [P1]

Enzymes speed up reactions by lowering the activation energy needed to for a reaction to occur, they are by definition catalysts. The interaction between an enzyme and substrate is what allows for a chemical to reaction to happen. Through this interaction substrates can be transformed into completely different molecules called the product.

Enzymes however cannot work when specific conditions are not met; the factors which decide how well they are able to function include temperature, pH levels and substrate concentration among others, but these are the main ones. The suitability of the environment will dictate how well they increase the speed of reactions.

Artwork by Tom Vickers, given to the world:)


As demonstrated by the diagram above the substrates bind to an enzyme by fitting into the active site, at this point the enzyme acts as a catalyst and can lower the activation energy needed so that a chemical reaction can take place, through this process the substrate will be converted into the product. The products are then released and the enzyme can take in new substrates and the cycle repeats itself (as a catalyst the enzyme is not altered in the chemical reaction, it simply lowers the energy activation).

Task 2 – Research in more details the main factors that affect enzyme activity. Make notes to help you explain these factors. You should research factors affecting enzyme functions in more detail, using graphs and detailed explanation for each factor. [M1]

Factors affecting enzyme functions:


  • As the temperature increases the energy activation needed for a chemical reaction to occur decreases,  yet only up to a certain point which is the “optimum temperature”, the point at which maximum reaction rate is achieved without the molecules being subjected to denaturation. Should the temperature become too high the molecules will be denatured and will not be able to perform their given role and are thus considered inactive. Not all enzymes have the same optimum temperature, in the human body the temperature needs to stay at around 37 degrees Celsius for the enzymes to work, at anything higher than 40 degrees Celsius there is great risk of denaturation for enzymes and other molecules.

These graphs shows how enzyme activity increases as the temperature increases, although only up to the optimum temperature, at which point the energy emanating from the heat denatures the enzyme.

By Nygma
(click to enlarge)




  • Enzymes have an optimum pH at which they work best and just like temperature it varies among different enzymes. The pH may alter the shape of an enzyme by breaking its bonds, which may result in the change of an active site (denaturation) that will not be able to fit with substrates, thus rendering the enzyme inactive.

These graphs shows how enzyme activity increase with the pH until it reaches its peak, the optimum pH, at which point activity sharply falls due to denaturation.

Substrate saturation

  • Substrate concentration increases the rate of reaction by making more substrates available, however if there are too many substrates to the point of saturation (this occurs when the active site of a substrate is occupied/ blocked by another substrate rendering the enzymes unable to bind with them) then the rate of the reaction will neither speed up or increase but stagnate.

These graph shows the effect that substrate saturation has on the rate of reaction with enzymes. The rate of reaction increases as the number of substrate increases until it reaches its peak, which is when all active sites are occupied because of the number of substrates and the rate of reaction neither increases nor decreases but stagnates.

 Task 3 – Using the data attached explain why it is important that the optimum conditions are present for enzymes to function correctly. [D1]

In the handout, we can observe that the enzyme pepsin which is mixed with egg whites function only under certain conditions. The ones which can be observed in the handout are pH levels and temperature, throughout the experiment different levels of pH were used to identify the optimum pH level pepsin would need to be under for maximum production of amino acids. Temperature is also an important factor, in the second part of the handout shows how temperature controls the optimum conditions of pepsin.

As explained in the handout, pepsin is an enzyme which breaks down protein into amino acids. When added to the egg whites we can observe the chemical reaction which takes place and conclude that based on how cloudy the solution is, we can evaluate if a chemical reaction is taking place and if so how fast.

It is evident that there is no or too little a reaction taking place when the pH levels are at or above neutral levels, indicating that an alkali environment is unsuitable for pepsin to function in correctly (it becomes inactive). Once pH levels of 5 or lower are used a chemical reaction can be seen to occur as the solution turns clear, indicating that pepsin is transforming protein into amino acids. The best results are observed when ph levels are at 3 when the solution is noted to be clear after 10 minutes, while when at pH 5 the solution takes 20 minutes to turn clear; demonstrating that although the pepsin is working it is not doing so optimally because the reaction takes much longer to occur.

Having found a pH level which delivers results, it is used again but this time in conjunction with water to observe if it is the ph level or in fact pepsin that is making the solution turn clear and since it remains cloudy then pepsin is clearly the factor which is inducing a chemical reaction.

In the temperature graph, the letter A on the curve corresponds to the moment when the rate of reaction is increasing with the temperature, while the letter B corresponds to the optimum temperature because it is the highest point of the rate of reaction, from then on its decreases until it reaches the letter C, indicating that pepsin becomes inactive should the heat become too high.

Pepsin can be found in the digestive system of many animals including humans and is produced by the stomach. This organ produces hydrochloric acid which is a very strong acid (pH levels between 1 and 2) and can provide a suitable environment for pepsin to work in. Furthermore the average temperature in the human body is 37 degrees Celsius, which correlates with the temperature used in the experiments, as we can observe from the graph this is the optimum temperature for pepsin to work in.

In conclusion, the experiment reinforces the above information, by finding result which confirms that pepsin works best in an acidic environment. Concerning temperature, it is observed that pepsin works best under conditions close to 37 degrees Celsius, anything lower or higher will result in sub par performance from the enzyme. This behaviour can be applied to all enzymes, without suitable conditions enzymes are unable to perform at their best and sometimes not all if denaturation occurs. This highlights the need for enzymes to be under specific conditions to work and in even more precise ones to work at their best; their “optimum condition”.


GCSE Core science GCP

BTEC level 2 Applied Science Edexcel 2010



 Enzyme, denaturation, enzyme assay [Wikipedia]

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