Enzymes

Reactions

• Most reactions take place in a number of steps which need to be carefully controlled if the cell is to function properly

• Enzymes are the most important controllers of cellular reactions

Catalysts

• Catalysts speed up reactions without themselves being involved in the reaction

• Enzymes are catalysts made of protein they speed up a reaction without being used up themselves in the reaction

• Because enzymes are made in living things they are called biological (or organic catalysts)

• We learned in the chapter on food that proteins are made when amino acids join together

• The function of a protein is decided not only by the sequence of amino acids but also by the way the protein folds

• Most enzymes are globular proteins

Learning Check

• What is an Enzyme?• What are catalysts?• To what group of bio-molecules do

enzymes belong?

How enzymes work

• Enzymes are not flat they have a 3D structure

• Each enzyme has its own specific shape that will only “fit” the molecule that the enzyme is designed to work on

• If the enzyme that breaks starch into glucose meets a fat molecule it will not fit it and will not be able to work on it

A movie on the action of Enzymes!

• http://www.bishopstopford.com/faculties/science/arthur/?sortby=3

• http://www.angelo.edu/faculty/nflynn/Biochemistry/

http://www.angelo.edu/faculty/nflynn/Biochemistry/

Learning Check

• Why is the shape of an enzyme important?• Are enzymes flat, 3D or 2D in shape?

Enzyme Action

• The substance that an enzyme acts on is its substrate

• The substance(s) that the enzyme forms is called the product(s)

A Catabolic enzyme

• Amylase converts starch to maltose

• Catabolic as it breaks a big molecule into a smaller one

• It is produced by saliva glands in mouth and by the pancreas

An Anabolic Enzyme

• DNA Polymerase forms and repairs DNA

• Anabolic as it coverts simpler molecules into more complex molecules

• Found in almost all living things

Consider This

• Amylase is an enzyme found in saliva. It breaks starch molecules into smaller maltose molecules

• What is the substrate?• What is the product?• Will amylase break fats into fatty acids +

glycerol? Why?• Is this an example of a catabolic or an anabolic

reaction? Why?

And This

• DNA Polymerase is an enzyme that builds DNA using tiny molecules in our cells

• What is the substrate?• What is the product?• Will amylase build keratin out of peptides?

Why?• Is this an example of a catabolic or an

anabolic reaction? Why?

• Enzymes work because they have the correct shape to fit the substrate

• They have a complex 3 dimensional shape to fit the substrate

• When enzymes and their substrates meet and come together they form an Enzyme/Substrate complex

Learning Check

• What is meant by a substrate?• What is the unit formed when an enzyme

combines with its substrate called?• Give an example of an anabolic reaction• Give an example of a catabolic reaction

Reversible

• Enzyme Reactions are reversible

• Like a key can open or close a lock enzymes can make reactions go in either direction

Example

• In the following example the enzyme can break molecule X into Y+Z but it can also combine Y+Z to form X

X Y + Z

Learning Check

• Can enzyme reactions be reversed?

Naming Enzymes

• Enzymes are named by adding the suffix ase to the name of their substrate

Eg. • Enzyme that acts on Amylose (starch) is

called amylase• Enzymes that act on proteins are called

proteases

Learning Check

• Can you think of a name for enzymes that act on Lipids?

• Amazingly enough they are called Lipases!

Inhibitors

• Inhibitors attach to enzymes and destroy their shape

• When this happens the enzymes are said to be denatured

Nerve Gases

• The nerve gases we hear of terrorists using are often inhibitors that attach to enzymes involved in our nerve transmissions

Poisoning people the old fashioned way!

• Cyanide denatures an enzyme involved in respiration

Beneficial Inhibitors

• Insecticides affect enzymes in insects causing their death

• Drugs can affect enzymes involved in pain causing the pain to stop

• Antibiotics can affect enzymes in bacteria causing the bacteria to die

Learning Check

• What is an inhibitor?• How do inhibitors work?• Can you give an example of a harmful

inhibitor?• Can you give an example of a beneficial

inhibitor?

Enzymes at work!

Enzymes work best in certain conditions

Factors that affect enzymes include• Temperature• pH• Substrate concentration• Enzyme concentration

We will be examining these in experiments

Temperature

• At very low temperatures ice forms, liquids become solids and enzymes can’t work

• As temperature increases molecules start to move and bump into each other causing the rate of reaction to increase

• Human enzymes work best at body temperature (37°C)

• Plant Enzymes work best at 20-30 °C

• Above certain temperatures enzymes start to lose their shape the rate of reaction falls

• When the shape is fully lost the enzyme is said to be denatured this is usually a permanent condition

Optimum Temperature

pH

• pH scale goes from 0 -14• 0-7 is acidic • 7-14 is basic (or alkaline)

Optimum pH

• Enzymes work over a very narrow pH

• Most enzymes work at pH 6-8

• Outside this they lose shape and get denatured

• The optimum or best ph is usually pH 7

An Exception!

• Is our stomach acid or basic?• Do you think there are enzymes in our

stomach?• Pepsin is an enzyme in the stomach that

works best at pH 2!

Learning Check

• What factors affect enzyme action?• What is the best temperature for (a)

human enzymes and (b) plant enzymes• What is meant by pH?• Do enzymes work over a narrow or wide

pH range?

Immobilised Enzymes

• Bio-processing is the use of enzyme controlled reactions to produce a product

• Bio-processing can be used to produce a vast range of products such as cheeses, beer, antibiotics, vaccines, methane gas, food flavours, vitamins and perfumes

Bioprocessing

• Traditionally micro-organisms such as bacteria and yeast were used but since the 1900’s and especially since the 1950’s enzymes are being used

Immobilized Enzymes

• If enzymes are used freely dissolved in a vessel it can be very wasteful as they are lost at the end of the process

• To prevent this problem enzymes are often immobilised or fixed

• This means they are attached to each other or an inert substance and can be used repeatedly

Learning Check

• What is bio-processing?• What type of organisms are uasually used

in bio-processing?• Why is bio-processing advantageous?

How to immobilise enzymes

• Physical methods• Adsorption where enzymes are

physically attached to inactive supports such as glass beads or ceramics

• Enclosed by a membrane when enzymes are kept within a membrane

• Trapped in a gel, sodium alginate is commonly used this allows substrates in and products out

• Chemical Methods

• Bonded to a support enzymes chemically bonded to a support such as glass beads or ceramics

• Bonded to each other Enzymes are chemically bonded to each other

Learning Check

• Describe 2 physical methods of immobilising enzymes

• Describe 2 chemical methods of immobilising enzymes

Advantages of Immobilised Enzymes

• Efficiency of enzyme is not affected

• Immobilised enzymes can be easily recovered from the product so you can get a pure sample of product easily

• Immobilised enzymes can be reused this cuts costs

• Enzymes frequently become more stable when immobilised

Uses of Immobilised Enzymes

• Immobilised glucose isomerase converts glucose to fructose which is used to sweeten drinks

Antibiotics

• Penicillin acylase changes the structure of penicillin to make more antibiotics that will fight a wider range of bacteria

Lactose

• Lactase converts lactose to sweeter sugars glucose and galactose which are then used by food manufacturers

Learning check

• What are the advantages of immobilising enzymes?

• Can you name 3 things immobilised enzymes are used for?

Syllabus Can you.......

• Define the term: enzymes• State the nature, folded shape & functions of

enzymes.• Explain the role of enzymes in plants and

animals including role in metabolism• Explain the effects of pH & temperature on

enzyme activity.• State the procedure and advantages of Bio-

processing.• State the use of Bio-processing.