Module 1: Enzymes Biology

State that enzymes are globular proteins, with a specific tertiary structure, which catalyse metabolic reactions in living organisms

State that enzyme action may be intracellular or extracellular

Describe, with the aid of diagrams, the mechanism of action of enzyme molecules, with reference to specificity, active site, lock and key hypothesis, induced-fit hypothesis, enzyme-substrate complex, enzyme-product complex and lowering of activation energy

Specificity, Active Site, Enzyme-substrate complex and Enzyme-product complex All enzymes contain an active site which is usually a depression within the enzyme that another molecule can bind to. This molecule is a substrate, and the substrate must be the exact same shape as the enzyme in order for it to bind and create an enzyme-substrate complex. The substrate must be specific to the active site. Once the enzyme-substrate complex is made, it catalyses the reaction. This may cause the substrate to split into two or more molecules, or catalyse the joining together of two molecules. Either way, it forms an enzyme-product complex and from that two or more products.

Lock and Key Hypothesis The lock and key hypothesis basically states that the substrate fits the active site perfectly without any help or change in shape. This is shown in the image above.

Module 1: Enzymes Biology

(cont.) Describe, with the aid of diagrams, the mechanism of action of enzyme molecules, with reference to specificity, active site, lock and key hypothesis, induced-fit hypothesis, enzyme-substrate complex, enzyme-product complex and lowering of activation energy

Induced-fit Hypothesis This is where the whole enzyme changes shape slightly in order to accommodate the substrate and hold it in exactly the right position in order to allow the reaction to occur. Lowering of Activation Energy Enzymes lower the activation energy needed to start a reaction by holding their substrates in such a way that their molecules can react more easily. Reactions catalysed by enzymes take place rapidly at a much lower temperature than they would without them.

Describe and explain the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme activity

pH The optimum pH of most enzymes is 7 (neutral), however, some enzymes work better in acidic conditions, for example, pepsin, which is found in the stomach. If the optimum pH changes by a considerable amount, the tertiary structure of the enzyme can be affected and can cause denaturation of the enzyme. Temperature As the temperature rises, the enzyme and substrate molecules move faster, meaning collisions happen more frequently and so more enzyme-substrate complexes are made. They also react with more energy meaning they are more likely to have sufficient activation energy to react. The enzymes optimum temperature is when the rate of reaction is at its fastest. However, if the temperature becomes too high, the bonds (especially hydrogen bonds), can start to break. This affects the tertiary structure of the enzyme and can cause it to fall apart and denature the enzyme. Enzyme concentration If the enzyme concentration increases, the rate of reaction will initially increase. This is because the chances of a substrate binding with an enzyme are increased – the number of collisions is raised. However, after a certain time the rate of reaction will start to decrease because the number of substrates decreases.

Module 1: Enzymes Biology

(cont.) Describe and explain the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme activity

Substrate concentration This is similar to enzyme concentration. If the substrate concentration increases, the rate of the reaction will initially increase. This is because if there are more molecules present there is more likely to be a collision and therefore a reaction. However, as the reaction progresses, and the substrate concentration remains high yet the enzyme concentration isn’t affected, the enzyme concentration will go down as they bind with substrates. The enzymes simply cannot work faster and starts to work at its maximum possible rate, known as Vmax.

Describe how the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme activity can be investigated experimentally

1. Set up the equipment needed to carry out the test. 2. In one test tube, add a measured amount of

substrate and a measured amount of enzyme. Add either an acid or alkali and take tests at varying pH levels.

3. In another, do the same again but put a thermometer in the tube and heat it up, measuring the rate of reaction every xo.

4. In another, add a set amount of substrate but add a

lot of enzyme solution and take tests.

5.In another add a set amount of enzyme solution but add a lot of substrate solution and take tests.

Module 1: Enzymes Biology

Explain the effects of competitive and non-competitive inhibitors on the rate of enzyme-controlled reactions, including reference to both reversible and non-reversible inhibitors

Competitive Inhibitors Competitive inhibitors are ones that bind to the active site, rather than somewhere else on the enzyme. This means they are competing with the substrate to enter the active site. They aren’t the exact same shape as the enzyme’s respective substrate, though they are similar enough to allow the inhibitor to bind. This is reversible because if the substrate concentration is increased, it can detach from the enzyme and the proper substrate can bind with it. However, sometimes the inhibitor will bind permanently with the active site, and no amount of substrate can change that. This is irreversible. Non-competitive Inhibitors Non-competitive inhibitors are ones that bind to somewhere on the enzyme that isn’t the active site. They change the shape of the active site meaning the original substrate cannot bind there anymore. This can be reversible or irreversible, depending on how the inhibitor bonds with the enzyme (either briefly or permanently).

Explain the importance of cofactors and coenzymes in enzyme-controlled reaction

Most enzymes require the presence of another substance in order to function. These are called cofactors or coenzymes. These briefly attach to the enzyme and slightly alter the shape of the active site. This could be for a number of reasons, the most common one being the fact that changing the active site may allow the substrates to fit into the active site better. An example of this is that chloride ions act as cofactors for salivary amylase. They bind with amylase and slightly change its shape so that it can bind better with starch molecules.

Module 1: Enzymes Biology

State that metabolic poisons may be enzyme inhibitors, and describe the action of one named poison

Metabolic poisons may be enzyme inhibitors. Alpha-amanitin This poison is found in the death cap mushroom and will inhibit enzymes. The enzyme it inhibits are the ones that catalyse the production of RNA from DNA. If this poison does inhibit these enzymes, cells are no longer able to synthesise proteins.

State that some medicinal drugs work by inhibiting the activity of enzymes