ENZYMES summarized

Introduction

At this moment, thousands of chemical reactions are taking place inside your body. Chemical reactions are also taking place in the plants outside your window, and in all the other living things in the world. Every one of these reactions is being catalysed by an enzyme! Without enzymes, none of these reactions would take place. The enzymes make sure that all the reactions in living things happen at the right time, in the right place, and fast! This unit is about the way in which chemical reactions occur in living cells, and about the uses of enzymes in the food industry. Enzymes are proteins that function as biological catalysts. A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction. Every metabolic reaction is catalysed by enzymes. They control the speed of chemical reactions in every cell in the body. Enzymes help cells to carry out chemical reactions quickly and efficiently. Enzymes are not changed by the reaction they catalyse.

Properties of enzymes
Enzymes:
• are proteins
• are biological catalysts
• are specific in the reactions they catalyse; one
• enzyme will affect the rate of only one reaction
• are not changed by the reaction they catalyse
• can be used over and over again
• are needed in small quantities
• help cells to carry out chemical reactions quickly and efficiently at relatively low temperatures, this would not be possible without the help of enzymes
• are affected by temperature
• are affected by pH
• have a lower activation energy.

Metabolic Reactions
Metabolic reactions are all the chemical reactions that occur in cells. They include reactions that are catalysed by enzymes. There are two types of reactions - anabolic and catabolic: Anabolic reactions build up complex compounds from simpler ones, for example, making sugars from carbon dioxide and water during photosynthesis. Catabolic reactions break down complex compounds into simpler ones with the release of energy, for example, digestion of food reserves to release energy during the germination of seeds.

Metabolic reactions are organised into step-by-step sequences called metabolic pathways. The enzymes for a particular pathway usually occur together, often in the cell organelles. For example, the enzymes for photosynthesis occur in the chloroplasts; those for release of energy during respiration occur in the mitochondria. One important group of enzymes are the digestive enzymes that help you to break down your food. One of these digestive enzymes is called amylase and it acts on starch.

Classification of enzymes
The names of the different types of enzymes usually end in the letters -ase. Three of the most common enzymes with their chemical actions are:
• lipase -breaks down fats
• protease -breaks down proteins
• carbohydrase-breaks down carbohydrates.

Let us also look at other essential enzymes:
• Hydrogenases catalyse the removal of hydrogen atoms.
• Oxidases catalyse the addition of oxygen to hydrogen.
• Hydrolases catalyse the addition of water, or break bonds by the addition of water.
• Ligases catalyse the synthesis of new C-O, C-S, C-C or C-N bonds joining together molecules.

How do enzymes work?
Enzymes work in the same way as catalysts; they can work with only one substrate and they can be used more than once. In other words, enzymes work as a lock and a key.

Substrates and products
Enzymes catalyse reactions. In a reaction, one or more substances are changed into different substances. The substance that is present at the beginning of the reaction is called the substrate. The substance it is changed into is called the product. Enzymes have a structure that is called the active site. Only one substance can fit into the active site to be digested, and it is the only substrate that this particular enzyme works with. *Note it, The active site only fits the shape of the substrate molecule, but not the shape of any other kinds of molecules*

Active sites and enzyme specificity
Enzymes are specific in the reactions they catalyse because of their unique three- dimensional shape. The active site on the surface of the protein molecule of the enzyme molecule has a shape into which the smaller substrate molecule will fit. The substrate molecule breaks down to form products while attached to the active site. Once the products are formed, they leave the active site.

Look at Figure above to help you understand what happens when an enzyme catalyses a reaction:
• A substrate molecule collides with a molecule of its specific enzyme; the substrate molecule then binds to the active site of the enzyme molecule like a key fitting a lock.
• An enzyme-substrate complex is formed.
• The enzyme then releases the product(s) of the reaction.
• The enzyme is free to form an enzyme-substrate complex with another substrate molecule.
You can also think of enzymes working in the same manner as a key and a lock - the key is the substrate and the lock is the enzyme. The key should be exactly the right shape to fit in the lock, as should the substrate to fit in the active site of the enzyme. The key could open only one lock, and the lock could be unlocked by only that key. The  Figure  below illustrates this.

Lock and key mechanism

The action of an enzyme can be compared with a lock and a key. A lock can be unlocked or locked by using a specific key, if the projections in the lock fit into the corresponding slots in the key.

The lock can be compared with the enzyme because: • it can be used over and over again
• it can open a door (catabolic reaction) and can close a door (anabolic reaction)
• only a specific key can open a specific lock
• only part of the lock (active site) plays a role in opening the lock
• when heated, the lock (active site) will melt, lose its shape and will no longer be able to be opened by the key.

TRY THIS EXPERIMENT

This practical activity may take you about 30 to
40 minutes to complete.
For this practical activity, you should be able to
find most of the things you need. You can get iodine solution and a dropper pipette or plastic syringe from a pharmacist. You are going to use an enzyme in your own saliva. The enzyme is called amylase. Its function is to speed up the digestion of cooked starch. Amylase changes starch into a sugar called maltose.
You will need:
• a piece of starchy food that has been cooked, such as cooked potato or a piece of bread
• some iodine solution
• two containers, such as glasses or cups
• a white saucer or piece of tile
• a dropper pipette or plastic syringe
• a spoon to mix the food.
Method:
1. Mix a small piece of your starchy food in some water. You want to make about 40-50 cm3 of a smooth, runny liquid that is not too thick. The liquid should fill your container to a height of 2-3 cm.
2. Take up a small amount of the liquid into your dropper pipette. Put the liquid onto your saucer or white tile. Add a drop of iodine solution. It should appear very dark blue or black, which shows that there is starch present. Now wash out your dropper pipette and clean the saucer/white tile.
3. Divide the starchy liquid into two equal amounts. You need about 20 cm in each container. This should fill your container to a depth of about 1 cm.
4. Place some of your saliva into a cup. You need about 10 cm?
5. Add your saliva to the starchy liquid in one container. Stir it. Add an equal amount of water to the starchy liquid in the other container. Stir it.
6. Leave both containers in a warm place for about 10 minutes.
7. Take a small amount of the liquid from one container, and put it on the saucer or tile. Add some iodine solution, and note the result. Do the same with the liquid from the other container, remembering to wash out your pipette first!
8. If there was no difference between the results for the liquids from the two containers, then leave them a bit longer and try again.

In your notebook, answer the following questions.
1. Why was it important to keep washing out the
dropper pipette?
2. Why was it important to have equal amounts of starch in each container?
3. Why was it important to add water to the
container that did not have any saliva added
to it?
4. Try to explain the results that you obtained. 

HERE ARE THE ANSWERS TO THIS..COMPARE WITH YOURS

1. It is important to wash out the pipette so that you do not mix any liquids. For example, if you get just one drop of saliva in the cup, which is not supposed to have any in it, this will spoil your results.
2. To make it a fair test. You need to keep everything exactly the same in the two lots of liquid, except the one thing you are interested in - which is the amylase.
3. To make it a fair test, by keeping the total volume the same in each container.
4. You should find that the liquid in the container with no saliva kept on turning black when you added iodine solution to it. This means that it contains starch. The liquid in the container with saliva should have turned black with iodine solution to start with. After a while, the iodine solution should have stayed orangey-brown when you added it to the liquid. This means that the starch had disappeared. The starch disappeared because it was changed into maltose by the amylase in the saliva.

Experiments and controls
Why do you think the starch liquid was divided into two sample containers, and saliva added to only one of them? This was done so that we can be sure that the reason the starch disappeared had something to do with the saliva. Otherwise, you would never know if the starch would not have disappeared anyway. The starch liquid without any saliva is called a control. A control gives you results with which you can compare the results of your experiment.

Effect of temperature and pH on enzyme activity
We shall look at two factors that affect the way in which enzymes work, namely temperature and pH. Each enzyme works best at an optimum temperature and an optimum pH. Above or below this optimum level, the effectiveness of the enzyme's activity is reduced. Temperature and pH both affect the shape of the active site, making the substrate molecule unable to fit into the shape. Extreme temperatures and pH will cause the enzyme to be destroyed. The enzyme is then said to be denatured.

The effect of temperature on enzyme activity
Look at the graph that describes the effect of temperature on enzyme activity

Do you know what your body temperature is Most people have a body temperature of about 37 °C. The enzymes that work in our bodies, such as the digestive enzyme amylase, work fastest at this temperature. In general, the warmer it is the faster a reaction happens. Enzymes are proteins. When the temperature is low, the molecules have less kinetic energy, therefore molecules move slowly and there are few collisions between the enzymes and substrates. The enzymes can be inactive at a low temperature, resulting in a very slow rate of enzyme activity.

An enzyme-controlled reaction at an optimum temperature and above the optimum temperature, showing the denaturing of an enzyme

However, if the temperature at which a reaction happens gets far above 40 °C, the active site changes shape permanently due to bonds. which are broken, the substrate will not fit in the active site and the enzymes are said to be denatured. This means that they cannot catalyse a reaction anymore, so the reaction stops. Look at the figure above that shows the denaturation of enzymes.

The effect of pH on enzyme activity
Scientists use a scale known as the pH scale to measure the strengths of acids and alkalis in a solution. The scale has a range of numbers from 1 for strong acids to 14 for strong alkalis:
• A neutral solution, such as a sugar or salt solution, has a pH of 7.
• An acid solution, such as vinegar or lemon juice, has a pH of less than 7.
• An alkaline solution, such as many cleaning liquids, has a pH of more than 7.

- Some enzymes work best in alkaline or slightly alkaline conditions that have a pH of 7 to 7.5. For example, amylase, the enzyme found in human saliva, works best at a pH of 7.0 to 7.5. Amylase digests starch to the sugar called maltose. Some enzymes work best in acid conditions that have a low pH. For example, pepsin, the enzyme produced in the human stomach, works best at a pH of 2, which is acidic. Pepsin digests proteins to polypeptides in the presence of hydrochloric acid. The effectiveness of enzymes is strongly influenced by pH. Each enzyme will only work effectively within a very narrow range of pH (see Figure below).

ENZYMES IN EVERYDAY LIFE
Enzymes in seed germination
A seed contains an embryo plant. The seed has a tough, outer coat that protects the embryo inside. Many seeds can stay alive for years, without growing. They are said to be dormant. When the conditions are right, perhaps when it gets warm enough or when it rains, the seed starts to germinate. It takes up water, the enzymes are activated, and the little embryo begins to grow into a plant. It grows a root and a shoot. In order to grow, the embryo plant needs food. It is too small to make its own food by photosynthesis as a fully grown plant can do. To begin with it has po light because it is probably germinating under the ground Seeds stores for the embryo to use while it grows. This is why we eat a lot of seeds in our diet. Mealie seeds, for example, contain a lot of starch and some protein. The plant stores substances in its seeds to feed the growing embryo plants. Starch is an insoluble substance, and the embryo cannot use it as a food supply, unless it is changed into a soluble substance. Seeds contain the enzyme amylase. The amylase, just like the amylase in your saliva, changes the starch in the seed into the sugar maltose. Maltose is soluble, and can dissolve in water in the seed and be carried to the embryo plant. The stored proteins also need to be changed to a soluble substance. The enzyme that does this is called protease. The amylase and protease in the seed will not start to work, until the seed starts to germinate. Often, it is water soaking into the seed that starts the enzymes working.

Enzymes in biological washing powders
Some stains on clothes are very difficult to remove. These tend to be biological stains, such as blood, sweat, egg and wine. Ordinary washing powders contain detergents that remove grease and dirt, but they have little effect on biological stains. Biological washing powders contain protein-digesting enzymes. These break down proteins in the stain, producing smaller molecules that are not coloured and easily removed by the detergent in the powder. Lipases will break down the fat stains, and proteases will break down protein stains, for example, blood.

Enzymes in the food industry
Enzymes are widely used to manufacture many types of food. The advantages of using enzymes are that they are specific to one substrate, usually fairly cheap to produce and can sometimes be reused. For example, protease is used to pre-digest proteins during the manufacture of baby foods, and fructose syrup can be produced from starch that has been obtained from maize (mealies). The enzyme amylase converts the starch into glucose, for example, as an ingredient in sports drinks and then another enzyme, isomerase, converts the glucose into fructose. The fructose is then used to make a very sweet fructose syrup that has a low caloric value.

Other uses of enzymes in the food industry
• In the baking industry, enzymes are used in the production of white bread, buns and rolls. Enzymes speed up the breakdown of the starch in flour into sugar; yeast can then act more easily on the sugar to release carbon dioxide and cause the dough to rise.
• In the dairy industry, enzymes help in the ripening of blue mould cheeses, such as Danish blue.
• In baby foods, they are used to partially break down food for easier digestion in the digestive tract of the baby.
•In fruit juice, enzymes are used to keep the juice clear.

The End... Stay Tuned For More! Posted by Mr DeHaan Ahil.