Enzymes

Metabolism Is the sum of all the chemical reactions that take place within an organism. It is the way in which energy is obtained and utilised within the cell.

Metabolic reactions Catabolic – complex molecules to simply molecules Anabolic – simple molecules to more complex molecules Examples?

Enzymes are the most important controllers of these cell / metabolic 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

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)

Revision!! Based on your nutrition chapter, what substrates do the following enzymes work on: Amylase Pepsin Lipase

And what are the products? Amylase – starch = Pepsin – proteins = Lipase – lipids =

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 Will amylase break fats into fatty acids + glycerol? 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

Enzyme Reactions are reversible Like a key can open or close a lock enzymes can make reactions go in either direction

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

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 Lipase act on lipids

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

Experiment Time!

To investigate the effect of temperature on Catalase (mandatory exp)

Above certain temperatures enzymes start to lose their 3D specific shape and the rate of reaction falls When the shape is fully lost the enzyme is said to be DENATURED (does not work)

Experiment Time!

To investigate the effect of heat denaturation on Catalase (mandatory exp)

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

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

Experiment Time!

To investigate the effect of pH on catalase (mandatory exp)

results pH 9

Result! Catalase should have a optimum pH of 9.

H2O2 CATALASE Water + oxygen Questions... Why is foam produced?? H2O2 CATALASE Water + oxygen

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

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

See next PP presentation “enzymes (immob)”