ENZYMESENZYMES

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Key Knowledge -Cell Functioning: General role of enzymes in biochemical activities of cellsKey Knowledge -Cell Functioning: General role of enzymes in biochemical activities of cells

DefinitionsDefinitions Enzyme (E)Enzyme (E): protein catalyst: protein catalyst

CatalystsCatalysts: speed up reactions : speed up reactions without being changed by the without being changed by the reactionreaction

Substrate (S)Substrate (S): reactant(s) in : reactant(s) in the enzyme-catalyzed reactionthe enzyme-catalyzed reaction

Active siteActive site: area of enzyme : area of enzyme where substrate(s) bind(s)where substrate(s) bind(s)

EnzymesEnzymes Are involved in every Are involved in every

biochemical reaction and biochemical reaction and thereby control metabolismthereby control metabolism

Enzymes are globular proteins Enzymes are globular proteins with a specific three-with a specific three-dimensional conformationdimensional conformation

Increase the rate of reaction Increase the rate of reaction without altering the enzymewithout altering the enzyme

EnzymesEnzymes A single enzyme molecule can catalyse thousands A single enzyme molecule can catalyse thousands

or more reactions a secondor more reactions a second.

Enzymes are unaffected by the reaction and are Enzymes are unaffected by the reaction and are reusable.reusable.

CofactorsCofactors

Many enzymes need cofactors (or coenzymes) to work properly. These can be metal ions (such as Fe2+, Mg2+, Cu2+) or organic molecules (such as haem, biotin, FAD, NAD or coenzyme A). Many of these are derived from dietary vitamins,

which is why they are so important.

Enzymes at workEnzymes at work 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. Enzymes have the ending -ase. The action of maltase on this reaction is usually written as::

maltase Maltose Maltose GlucoseGlucose

If there is too much glucose the enzyme can help the reaction to go in the opposite direction:

maltaseGlucose Glucose MaltoseMaltose

Because this reaction can go in either direction it is called a reversible reaction and it is shown with the arrows drawn in both directions:

maltaseMaltose Maltose GlucoseGlucose

Enzymes at workEnzymes at work

Proteases and peptidasesProteases and peptidases - - A protease is any enzyme that can break down a long protein into smaller chains called peptides .Peptidases break peptides down into individual amino acids. Proteases and peptidases are often found in laundry detergents -- they help remove things like blood stains from cloth by breaking down the proteins.

Amylases Amylases - - Amylases break down starch chains into smaller sugar molecules. Your saliva contains amylase and so does your small intestine. Maltase, lactase, sucrase finish breaking the simple sugars down into individual glucose molecules. .

Lipases Lipases - - Lipases break down fats. .

CellulasesCellulases - - Cellulases break cellulose molecules down into simpler sugars. Bacteria in the guts of cows and termites excrete cellulases, and this is how cows and termites are able to eat things like grass and wood.

SpecificitySpecificity Enzymes are highly specific with each enzyme acting on only one kind of Enzymes are highly specific with each enzyme acting on only one kind of

substrate substrate

Induced Fit ModelInduced Fit Model - there is some flexibility to the active site which can - there is some flexibility to the active site which can expand or contract to accommodate the substrateexpand or contract to accommodate the substrate

Enzyme-Substrate complexEnzyme-Substrate complex The substrate (S) binds to the active site of the enzyme (E) to form an The substrate (S) binds to the active site of the enzyme (E) to form an

enzyme-substrate complex (ES)enzyme-substrate complex (ES)

The enzyme and the substrate are held together by weak bonds The enzyme and the substrate are held together by weak bonds

Then the substrate is converted into product Then the substrate is converted into product while attached to the while attached to the enzymeenzyme, and finally the product is released., and finally the product is released.

The enzyme (E) is unchanged at the end of the reaction - it returns to The enzyme (E) is unchanged at the end of the reaction - it returns to its original shape after releasing Pits original shape after releasing P

How do enzymes speed up How do enzymes speed up reactions?reactions?

Enzymes lower the Enzymes lower the activation energyactivation energy (EA=amount of energy that reactant molecules require to start a reaction) of the chemical reactions that they catalyze

E-S binding causes a E-S binding causes a strain on the bonds in the strain on the bonds in the substratesubstrate

Factors affecting enzyme activityFactors affecting enzyme activity

1. TEMPERATURE1. TEMPERATURE

Increases rate of reaction by Increases rate of reaction by increasing kinetic energy so increasing kinetic energy so that molecules collide more that molecules collide more frequentlyfrequently

Eventually at a certain Eventually at a certain temperature enzymes are temperature enzymes are denatured and will not functiondenatured and will not function

• Denaturation - a structural change in a protein that results in a loss (usually permanent) of its biological properties

Optimum temperature

Enzyme denatures

Factors affecting enzyme activityFactors affecting enzyme activity

2. pH2. pH

Can change enzyme shape by Can change enzyme shape by changing the charge on amino changing the charge on amino acidsacids

Enzymes have an optimal pH at which they function best

e.g. pepsin pH optimum is 2

e.g. trypsin pH optimum is 8

pH can also denature enzymes pH can also denature enzymes by changing state of ionization by changing state of ionization of R groupsof R groups

Factors affecting enzyme activityFactors affecting enzyme activity

3. SUBSTRATE CONCENTRATION3. SUBSTRATE CONCENTRATION Reaction rate increases with increasing

substrate concentration

There is a limit to this increase however - once all active sites are occupied (saturated), adding more substrate will not increase the reaction rate

4. ENZYME CONCENTRATION4. ENZYME CONCENTRATION

As the enzyme concentration increases the rate of the reaction increases linearly, because there are more enzyme molecules available to catalyse the reaction. At very high enzyme concentration the substrate concentration may become rate-limiting, so the rate stops increasing. Normally enzymes are present in cells in rather low concentrations.

Factors affecting enzyme activityFactors affecting enzyme activity

5. Inhibitors5. Inhibitors molecules that bind to the substrate and change it so molecules that bind to the substrate and change it so

that the enzyme cannot bind to itthat the enzyme cannot bind to it

• e.g. e.g. cyanidecyanide binds to copper ions in cytochrome oxidase (final binds to copper ions in cytochrome oxidase (final enzyme in respiration) irreversiblyenzyme in respiration) irreversibly

• e.g. e.g. sarinsarin (nerve gas) binds to acetylcholinesterase irreversibly (nerve gas) binds to acetylcholinesterase irreversibly

Enzymes in biotechnologyEnzymes in biotechnology

At present, cellulases and related enzymes are At present, cellulases and related enzymes are used in food, brewery and wine, animal feed, used in food, brewery and wine, animal feed, textile and laundry, pulp and paper industries, textile and laundry, pulp and paper industries, as well as in agriculture and for research as well as in agriculture and for research purposes. Indeed, the demand for these purposes. Indeed, the demand for these enzymes is growing more rapidly than ever enzymes is growing more rapidly than ever before, and this demand has become the before, and this demand has become the driving force for research on cellulases and driving force for research on cellulases and related enzymes.related enzymes.

BrewingBrewing

Brewing uses the living organism yeast. Enzymes within yeast catalyse anaerobic respiration, which converts glucose solution into ethanol (alcohol) and carbon dioxide.

This reaction is called fermentation.

glucose → carbon dioxide + ethanol

Bread makingBread making

Fermentation is also used in bread making. Flour, water, sugar and yeast are the main ingredients in bread. The ingredients are mixed together to make a dough. This dough is left in a warm place for an hour or two. During this time, fermentation takes place and carbon dioxide is produced. It is the carbon dioxide that helps to make the bread rise when the dough is cooked in an oven.

Biological washing powdersBiological washing powders

One common use in the One common use in the home is in biological home is in biological washing powders. The washing powders. The enzymes are supposed to enzymes are supposed to digest protein stains from digest protein stains from the clothes. Since the clothes. Since enzymes work at a low enzymes work at a low temperature this saves temperature this saves electricity and makes electricity and makes them good for delicate them good for delicate fabrics. fabrics.

Wider uses of enzymesWider uses of enzymes

Enzymes are used in many industrial processes. Enzymes are used in many industrial processes.

Some of the enzymes and the products are:Some of the enzymes and the products are:

Amylases- used in textile and paper productionAmylases- used in textile and paper production Ficin- used in photographic processesFicin- used in photographic processes Pepsin - used in the pharmaceutical industryPepsin - used in the pharmaceutical industry Bacterial proteases- used in making leather, Bacterial proteases- used in making leather,

textiles and in laundrytextiles and in laundry Catalase- used in rubber productionCatalase- used in rubber production

Enzyme deficiencyEnzyme deficiency Most genetic disorders are due Most genetic disorders are due

to a deficiency in enzyme to a deficiency in enzyme functionfunction

PKUPhenylketnonuria is an inborn error of metabolism in which a missing enzyme causes the amino acid phenylalanine to build up, with devastating effects on the nervous system unless the individual follows a restrictive diet.

Enzyme deficiencyEnzyme deficiency

Lactose intoleranceLactose intolerance - - The inability to digest lactose (the sugar in milk) is caused by a missing lactase gene. Without this gene, no lactase is produced by intestinal cells. .

Albinism -Albinism - In albinos, the gene for the enzyme tyrosinase is missing. This enzyme is necessary for the production of melanin, the pigment that leads to suntans, hair color and eye color. Without tyrosinase, there is no melanin.

Cystic fibrosisCystic fibrosis - - In cystic fibrosis, the gene that manufactures the protein called cystic fibrosis transmembrane conductance

regulator is damaged.

Quick QuizQuick Quiz 1. What is an enzyme? 2. One characteristic of an enzyme is that it is

unchanged at the end of a reaction. Give two more characteristics of an enzyme. 3. Draw a graph to show the effect of changing the

temperature on the rate of an enzyme-catalysed reaction.

4. Draw a graph to show the effect of changing the pH on the rate of an enzyme-catalysed reaction.

5. What happens to an enzyme when it is denatured? 6. Give two conditions that will denature an enzyme. 7. List four industries that use enzymes.