Enzymes are biological catalysts that speed up chemical reactions in living organisms. There are more than five hundred different enzymes in every cell of the body, each of them helping the cell, and the body as a whole, to work.
Enzymes are involved in all biological processes and reactions, e.g. cellular respiration, photosynthesis and protein synthesis. Without enzymes these vital reactions would be too slow for life to continue.
Some enzymes work inside cells, while other enzymes (like digestive enzymes) work outside the cell.
Examples of enzymes
Each enzyme can usually only be the catalyst for a single reaction. For example, the enzyme maltase is the catalyst for changing maltose into glucose. Notice that the name of the enzyme is usually very similar to the substance it works on: maltase works on maltose. Enzymes have the ending -ase. While maltase can convert maltose to glucose, it cannot take two glucose molecules and put them together to form maltose. An enzyme can only do ONE job, in ONE direction.
The action of maltase on this reaction is usually written as:
(2)
Some enzymes help to make new substances in the body and others help to break down unwanted substances in the body. Enzymes not only speed up reactions, they are also located or released in very specific places, at specific times. This helps to ensure that all reactions happen in the right place and at the right time.
In the digestive system, enzymes break down large insoluble molecules (e.g. starch, proteins and fats) into small soluble molecules that can be absorbed into the blood from the small intestines.
Large
Insoluble
Molecule
Carbohydrate
(e.g. Starch)
Protein
Type of
Enzyme
Amylase
Carbohydrase
Protease (e.g. pepsin)
Fat/Lipids Lipase
Small Soluble
Product
Starch-> maltase
Maltose-> glucose
Proteins 
Amino Acids
Lipids  Glycerol and Fatty Acids http://www.abpischools.org.uk/page/modules/enzymes/enzymes3.cfm?coSiteNavigation_allTopic=1
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Properties of enzymes
1.
Most are all proteins, which is one reason why we need protein in our diet.
2.
They are all biological catalysts. They speed up a reaction without being used up; this means they can be used over and over again.
3.
A small amount of enzyme can affect the change of a large amount of chemicals.
4.
The way enzymes work is affected by temperature, pH and pressure. They can be denatured
(lose their tertiary and quaternary structure, sometimes permanently) by excessive heat and extreme pH).
5.
While most reactions that enzymes work on are reversible, an enzyme is specific, which means that it controls only one reaction. So maltase only acts on breaking down maltose, and NOT on creating maltose.
How do enzymes work?
Enzymes are thought to have an area with a very particular shape. When a molecule of the right chemical for that enzyme comes along it will fit exactly into the shape. The area of particular shape is called the active site of the enzyme, as that is where the reaction takes place. The molecule that the enzyme works on is called the substrate. After the reaction has taken place and the products of the reaction leave the active site leaving it ready for another molecule of the chemical.
The active site of an enzyme has such a particular shape that only one kind of molecule will fit it, rather like a particular key fitting a lock. This is why enzymes are specific in their action.
Effect of Temperature and pH
Increasing the temperature increases the kinetic energy of the enzyme and substrate molecules so that they move faster and are more likely to collide. So increasing the temperature increases the rate of the reaction up to a certain temperature. This temperature is known as the enzyme’s optimum temperature. Different enzymes have different optimum temperatures. The enzymes in animal bodies work best at 37˚C.
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If the temperature is increased beyond the optimum the enzyme has so much kinetic energy that the bonds holding the enzyme molecule together start to vibrate and eventually break. The enzyme loses its specific shape so that the substrate no longer fits in to the active site. We say that the enzyme is denatured.
Enzymes also have an optimum pH. Different enzymes have different optimum pHs, e.g. pepsin found in the stomach works best at pH 2, which is why the stomach produces hydrochloric acid.
Although enzymes in our bodies work best at 37°C, some very special enzymes can even work well at
75°C and they form the basis of a technique used to make lots of DNA from tiny amounts found at crime scenes. This technique is called the Polymerase Chain Reaction (PCR) and uses an enzyme called
Taq polymerase – an enzyme that works best at 75°C. Taq is a nickname for Thermus aquaticus, a bacterium that happily survives and reproduces in hot springs - an environment that is lethal to other organisms.
Use of enzymes in the home
Enzymes can be taken out of organisms, purified and then used in science and industry.
One common use in the home is in biological washing powders. These contain amylase, lipases and proteases and break down any stains that contain carbohydrate, fat and protein. They therefore digest
“biological” stains from the clothes. Since enzymes work at a low temperature this saves electricity and makes them good for delicate fabrics.
Some people, however, are allergic to the enzymes and suffer skin problems.
Enzymes in food
Many enzymes are used in the preparation of many different foods.
For example, amylases which are present in yeast are used in brewing and baking to convert sugars into alcohol and carbon dioxide.
Proteases are used in tenderizing meat. Rennin is essential to create cheese.
Enzymes are used in many industrial processes.
Here are some examples of enzymes and their uses.
 Amylases – breaks down starch - used in textile and paper production
 Ficin - used in photography processes
 Pepsin – breaks down polypeptides - used in the pharmaceutical industry
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 Bacterial proteases - used in making leather, textiles and in laundry
 Catalase - used in rubber production
 Taq polymerase - used in amplifying DNA found at crime scenes
It is possible to attach enzymes to small beads made of alginate. Enzymes that have been fixed in this way are called immobilized enzymes. Immobilized enzymes are widely used in industry because it allows the reaction to flow continuously and the product will not be contaminated with the enzyme so will not need to be purified.
Uses of immobilized enzymes
 Immobilized enzymes are used in the production of
 lactose free milk for people who are lactose intolerant.
Immobilized sucrase can be used to convert sucrose into the much sweeter glucose and fructose to sweeten low calorie foods.
 Immobilized enzymes are used also used in glucose testing strips to measure glucose levels for diabetics.
Other things to consider
Many enzymes consist of a protein and a non-protein component (called the cofactor ). Cofactors may be:
 organic groups that are permanently bound to the enzyme ( prosthetic groups )
 cations - positively charged metal ions ( activators ), which temporarily bind to the active site of the enzyme, giving an intense positive charge to the enzyme's protein
 organic molecules, usually vitamins or made from vitamins ( coenzymes ), which are not permanently bound to the enzyme molecule, but combine with the enzyme-substrate complex temporarily.
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Name ___________________________
QUESTIONS:
1.
Describe an enzyme. Why are enzymes important to life?
2.
Define: a.
Substrate – b.
Active Site -
3.
Enzymes exhibit specificity. a.
What does this mean? b.
Why does it make sense that they are specific when considering the relationship between the enzyme active site and the substrate it acts on?
4.
Would enzymes in our digestive system be more likely to carry out dehydration synthesis or hydrolysis?
Why?
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5.
Why is it important that all enzymes are not found “everywhere.” In other words, why would the enzyme amylase (which breaks down starch) only be found in our digestive system and not in every part of our body. Think about this from an energy (within the body) conservation standpoint (meaning, it doesn’t make sense for an organism to waste energy…..)
6.
Since pH plays and important role in protein structure/function, would it make sense that an enzyme found in our stomach (pH 2) would not be that effective in the small intestine (pH 8)? Why?
7.
Enzymes work on a substrate, using an active site to assist with the reaction a.
Explain how lactase would work on lactose. Draw diagrams to illustrate, then explain using vocab. b.
Explain how sucrose synthase would work on fructose and glucose. Draw diagrams to illustrate, then explain using vocab.
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8.
Explain each graph below, using vocabulary including optimum, pH, enzyme activity, the name of the enzyme, and where the enzyme might be found (and what it is doing).
Hmm…… which enzyme would work best in our stomach????
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