The effect of substrate concentration on the rate of reaction of enzyme activity

Updated: Oct 23, 2019


Research question

Investigation on the effect of different substrate concentrations, which in this case are the manipulated hydrogen

peroxide concentrations on the rate of enzyme activity of catalase in liver on the decomposition of the hydrogen peroxide.

Introduction

Enzymes are biological catalysts that catalase in biochemical reactions in living cells. In enzyme reactions, a substrate binds to the active site on the enzyme, forming an enzyme-substrate complex where the enzyme breaks down the bonds in the substrate, creating a whole new bond and formation which will lead to the product and during and after the whole process the enzyme will remain unchanged, thus being able to react in other chemical reactions again.

In this case, the enzyme is catalase which is produced by the liver to break down hydrogen peroxide. This is a very common end product of a metabolism, but very toxic as well if accumulated in the body.

2H2O2 (l) ==> O2 (g) + 2H20 (l)

In this experiment, we will put liver pieces in distilled water and different hydrogen peroxide concentrated solutions for mixed with 2 drops of soap for 60s and measure the foam obtaining gas on top of the liver to measure the rate of enzyme activity. The reason to why the soap is used in this practical, it to be able to measure the gas made from the reaction, which can otherwise not be seen without the foam obtaining it. The manipulation of different substrate concentrations show us a variation of enzymes rate of reaction to see where the enzyme will have full reaction capacity and efficiency as well as in which cases the enzyme will react the least.

Background information

As mentioned above, enzymes are proteins and biochemical catalysts that are involved in chemical reactions and metabolism in living cells and organisms. They are globular proteins, with specific shapes and are usually specific for a type of reaction. (1) The part of the enzyme that acts as a catalyst is called the active site and the rest of the enzyme's role is to maintain its specific shape. A reaction occurs from random movements of the enzymes and substrates, and when a substrate/substrates attach to the active site of the enzyme, the reaction is triggered and the result is a product with new bonds and chemical structure.

Some examples of Enzymes are (2) :

  1. ATPase, breaks down ATP ⇒ ADP, producing energy

  2. Glycogen synthase catalyses the formation of glycosidic bonds between glucose molecules

  3. Lactase, breaks down lactose ⇒ glucose and galactose

  4. Catalase, breaks down hydrogen peroxide ⇒ water and oxygen

The reason to why enzymes are very important biological catalysts, is because most reactions inside the cell requires a very high temperature to get going, which would inevitably destroy the cell. However, when enzymes are used a lot lower activation energy for the reaction to start. How enzymes lower the activation energy, is by holding the molecules packet together increasing the chance of a reaction to occur and thus lowering the activation energy.

There are 2 hypothetic models on the enzyme reaction one being the “Lock and key model” and “The induced fit hypothesis”. (3) The lock and key model as the name implies sees the substrate as the key and the enzyme's active site as the lock being specifically modified and complementary to one another. It further explains that when in random movements the complementary substrate to an enzyme collide, the substrate attached to the active site creating an enzyme-substrate complex and producing a product with the enzyme remaining unchanged and ready to react again.

The induced fit model is a more recent and more accepted model with wide evidence and acceptance around the world. The hypothesis explains how the shape of the active site of the enzyme is not in fact complementary to the substrate and when it is near a substrate is changes its shape to be complementary to the substrate. (4) When the composition is specifically correct, an enzyme substrate complex is formed producing a product with the enzyme remaining unchanged, thus able to react again.

Factors affecting the rate of enzyme activity are the competitive and noncompetitive inhibitors, temperature, pH and substrate concentration.

Enzymes have a specific optimum rate of reaction at a certain temperature, pH, substrate concentration and inhibitors presence. In this case the enzyme catalase has an optimum temperature at 37 degrees Celsius and if the temperature would get too high the shape of the active site will be permanently altered, leading to the enzyme no longer working and getting denatured.

The enzyme's optimum pH is at 7 and if it would be too low or high the enzyme will generally lose its complete ability to be active in reactions. When comes to rate of reaction if substrate concentrations, at a certain level the rate of reaction will reach a plateau and increase in substrate concentration will thus no longer affect or increase the rate of reaction considering all the enzyme molecules would be saturated with substrates.

Last but not least the presence of inhibitors affect the rate of reaction of which depends on if the inhibitors would be competitive or noncompetitive. A competitive inhibitor, as the name suggests the active site of the enzyme would be uninvited to attach to any other substrate thus no longer reacting with any other substrate. (5) However, increase in substrate concentration will lead to the competitive inhibitors to instead compete with one another and thus many enzymes will be free on the active site to react with substrates. Non competitive inhibitors inhibit the enzyme by attaching to the allosteric site of the enzyme, which is no the active site leading to the active site changing shape permanently and no longer being able to react and in this case increase in substrate concentration will not let the enzyme activity reach the usual plateau as it would if it would be a competitive inhibitor.