5. enzymes

CIE IGCSE Biology: Enzymes

Enzymes

Catalyst: a substance that speeds up a chemical reaction and is not changed by the reaction.Enzymes: proteins that function as biological catalysts.

The enzyme action:

1. The substrate molecule fits onto the active site of the enzyme.2. The substrate molecule has a specific shape which fits only onto the active site of a specific enzyme in a

lock and key model in which the active site is the lock and the substrate is the key.3. The substrate molecule is brought closer together and broken down / build up (depends on the type of

reaction) forming a new product.4. The enzyme is not changed and is reused.

The effect of changes in temperature and pH on enzyme activityAt a very low temperature, the enzyme molecules and the substrate molecules are moving very slowly. As the temperature increases, their kinetic energy increases and they move faster. The higher the temperature, the faster they move around, and the more frequently they collide with each other. When they have more energy when they collide, it’s easier for the reaction to take place. So as the temperature rises, the rate of reaction also increases. However, at a very high temperature, the reaction starts to slow down because the enzyme molecules are beginning to denature. They lose their shape and the substrate no longer fits into the active site. In an extremely high temperature, the enzyme molecules are completely denatured so no reaction takes place. The temperature the enzymes work the best at is called the optimum temperature. Most enzymes in the human body have an optimum temperature around 37°C while most enzymes in plants have an optimum temperature of around 25°C.


At a very low or high pH, the enzyme molecules lose their shape so their substrate cannot fit into their active site. For example, pepsin is a protein-digesting enzyme (protease) that works in the stomach at a very low pH – pH2 which is why the stomach secretes hydrochloric acid. Amylase works best at pH 7 or slightly above and is found in the mouth.

Germination of Seeds1. The seed contains the following enzymes: amylase, maltase, lipase, and protease.

- Amylase breaks down starch in the seed into maltose. Maltose breaks down maltose into glucose. Glucose is then used in respiration to release energy.

- Lipase breaks down lipids into fatty acids and glycerol. Fatty acids are used to build up cell membranes.

- Protease breaks down proteins into amino acids which are used for growth.2. For the enzyme to work, it needs:

- Water to activate the enzyme as the enzymes break down substances by hydrolysis to break down large molecules into small molecules).

- Oxygen for aerobic respiration to release energy.- Warm temperature to provide the optimum temperature for a high enzyme activity.

Biological Washing Powder1. The hardest stains on clothes to remove are proteins and lipids.2. The biological washing powders contain the enzyme protease and lipase.3. Lipase breaks down lipids into fatty acids and glycerol4. Protease breaks down proteins into amino acids.5. It’s easier to clean when there are enzymes because you cannot remove lipids (fats) and proteins because

they are insoluble. Amino acids, fatty acids and glycerol are water-soluble so you can rinse them off easily. Breaking down the substances makes it easier to clean as they become soluble in water.

Food industryPectinase: when juice is squeezed out of apples to make a drink, an enzyme called pectinase is often added. Pectinase is an enzyme that breaks down the substances that hold the cell walls of the apple cells together. This makes it easier to squeeze out more of the juice. It helps to break down the substances that make apple juice look cloudy, turning it into a clear liquid that most people prefer.

Lactase: this enzyme breaks down lactose into glucose and galactose. This enzyme is used to digest lactose to make it safe for lactose-intolerant people.


The use of microorganisms and fermenters to manufacture the antibiotic penicillin and enzymes for use in biological washing powders:

In a fermenter, the microorganism grows in a liquid called the medium. The medium must contain everything that the microorganism needs to live and produce the desired product. Penicillium needs:

- Oxygen for respiration- A source of carbohydrates, such as sugar or starch for respiration- A source of nitrogen, such as ammonium phosphate to make proteins for growth- A suitable temperature – high enough to make sure the reaction happens so the fungus’ enzyme does

not denature.The fermenter is covered with a cooling water-filled jacket around to maintain an optimum constant temperature to prevent the enzymes from denaturing, and from losing its shape because as the fungus respires and releases heat so the temperature in the fermenter increases which would kill the fungus resulting in no penicillin.

Acids or alkali are added to maintain the pH and keep it constant as the enzyme needs an optimum pH to give the maximum yield, otherwise the enzyme activity slows down.


The process to obtain enzymes1. Bacteria are grown in fermenter2. Bacteria provided with substrate, feedstock, food substances, sugar3. Bacteria provided with oxygen for aerobic respiration4. Optimum temperature (26°C) and optimum pH 5-6 are set5. The mixture is stirred to prevent settling6. Bacteria grow and reproduce rapidly7. Bacteria/fungi secret enzymes – either intracellular which are obtained by filtering the bacteria/fungi

from the feedstock, crush and add water to make a solution and then by evaporation or extracellular which are extracted by filtering directly

The growth of fungus slows down and stops at a point because the nutrients get used up, there are limiting factors, waste products build up and they are toxic, penicillin could inhibit growth and population reaches carrying capacity.

To make enzymes for biological washing powders, different bacteria or fungi are used in the medium depending on what enzymes they make.

5. enzymes

Documents