EnzymesEnzymes

Pathway organisersPathway organisers

The ushers of chemical reactionsThe ushers of chemical reactions

What is an enzyme?What is an enzyme? A biological A biological catalystcatalyst, speeding up the , speeding up the

rate of a reaction.rate of a reaction.

Catalysts are chemical substances Catalysts are chemical substances that help to speed up a reaction that help to speed up a reaction without being used up. (They are not without being used up. (They are not reactants.)reactants.)

They are only needed in small They are only needed in small amounts and are re-useableamounts and are re-useable

Enzymes - Biological Enzymes - Biological CatalystsCatalysts

Enzymes are all proteinsEnzymes are all proteins They allow biochemical reactions to They allow biochemical reactions to

happen in conditions that the body happen in conditions that the body can tolerate can tolerate

Some biological reactions would Some biological reactions would never happen without enzymes, they never happen without enzymes, they would require very high temperatures would require very high temperatures that living things could not survive inthat living things could not survive in

Enzymes - ProteinsEnzymes - Proteins To understand how enzymes work, you To understand how enzymes work, you

will need to know about protein will need to know about protein structure.structure.

Proteins are very long polymers that Proteins are very long polymers that become folded up to form 3D shapesbecome folded up to form 3D shapes

This folding occurs in a series of steps:This folding occurs in a series of steps: PrimaryPrimary SecondarySecondary TertiaryTertiary

Primary structure refers to the order of amino acids that make up

the chain

Secondary structure refers the folding of the structure

into coils (helix) or

pleated sheets. This is caused by hydrogen

bonds between the amino

acids

Tertiary structure refers

to how the helices and

pleats interact to make the

protein fold in to a 3D

globular shape. This is due to many different

types of bonding

Quaternary structure refers

to the interaction of one protein with another

Enzymes – Biological Enzymes – Biological CatalystsCatalysts

Enzymes work by bringing molecules Enzymes work by bringing molecules together or positioning them in a way together or positioning them in a way that makes the reaction happen more that makes the reaction happen more quickly.quickly.

The molecules that enzymes act on are The molecules that enzymes act on are called called substratessubstrates

Enzymes are very specificEnzymes are very specific The part of the enzyme that comes into The part of the enzyme that comes into

contact with the substrate is called the contact with the substrate is called the active siteactive site

For enzymes, tertiary is the most important aspect of the protein structure. It creates grooves in specific shapes. Such grooves then form the active site which fits the substrate(s) perfectly

If anything disrupts the tertiary structure of the protein, the active site may be changed. If the active site is changed, the enzyme will no longer be functional

Enzyme + SubstrateEnzyme + Substrate

Enzymes for buildingEnzymes for building

Enzymes for breakingEnzymes for breaking

Jobs that enzymes performJobs that enzymes perform

Enzymes work on a variety of Enzymes work on a variety of reactions; both catabolic and anabolic:reactions; both catabolic and anabolic: The breakdown of glucoseThe breakdown of glucose The production of ATP (cellular The production of ATP (cellular

respiration)respiration) The destruction (lysis) of worn out cellsThe destruction (lysis) of worn out cells Breakdown of toxic substancesBreakdown of toxic substances Cell divisionCell division Digesting food that is eatenDigesting food that is eaten

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

Enzymes are Enzymes are able to lower able to lower the ‘activation the ‘activation energy’ energy’ required to get required to get a reaction a reaction startedstarted

Reaction RateReaction Rate

The suffix ‘–ase’ is often used in enzyme The suffix ‘–ase’ is often used in enzyme names. names. AmylaseAmylase MaltaseMaltase LactaseLactase CatalaseCatalase LipaseLipase ProteaseProtease

Exceptions: pepsinExceptions: pepsin

Enzymes – ‘ase’Enzymes – ‘ase’

Factors affecting enzyme activityFactors affecting enzyme activity Enzyme concentration – more enzyme = faster Enzyme concentration – more enzyme = faster

reactionreaction Substrate concentration – more substrate = faster Substrate concentration – more substrate = faster

reactionreaction pH (acid or base) – depends on enzyme, mostly pH pH (acid or base) – depends on enzyme, mostly pH

77 Temperature – depends on enzyme, usually best at Temperature – depends on enzyme, usually best at

25-4025-40˚C˚C Denaturation – irreversible destruction of active Denaturation – irreversible destruction of active

site due to exposure to extreme conditionssite due to exposure to extreme conditions Inhibition – presence of other molecules which Inhibition – presence of other molecules which

slow down or prevent enzyme activity by blocking slow down or prevent enzyme activity by blocking active siteactive site

Substrate & Enzyme Substrate & Enzyme Conc.Conc.

Temperature & pH: Temperature & pH: Optimal ConditionsOptimal Conditions

Each enzyme will work best at a Each enzyme will work best at a specific temperature and specific pHspecific temperature and specific pH

This is because pH and temperature This is because pH and temperature can greatly affect the tertiary structure can greatly affect the tertiary structure of the enzyme and change the active of the enzyme and change the active sitesite

Examples of Optimum pHExamples of Optimum pH

DenaturationDenaturation All proteins (including enzymes) can All proteins (including enzymes) can

have their tertiary structure disrupted have their tertiary structure disrupted permanently. This is called permanently. This is called denaturationdenaturation

This can happen if the enzyme is:This can happen if the enzyme is: Overheated (beyond ideal temperature)Overheated (beyond ideal temperature) Exposed to extreme changes in pHExposed to extreme changes in pH Exposed to a toxin which irreversibly Exposed to a toxin which irreversibly

binds to the active sitebinds to the active site

Denaturation – the irreversible disruption of an enzyme’s tertiary structure, causing it to become totally inactive

InhibitionInhibition Enzymes can be affected by the Enzymes can be affected by the

presence of other moleculespresence of other molecules Molecules which decrease enzyme Molecules which decrease enzyme

activity are called inhibitorsactivity are called inhibitors There are 3 main types of inhibitors:There are 3 main types of inhibitors:

CompetitiveCompetitive Non-competitiveNon-competitive Toxins/poisonsToxins/poisons which bind irreversibly to which bind irreversibly to

the active sitethe active site

Competitive InhibitorsCompetitive Inhibitors Competitive inhibitors bind to the active Competitive inhibitors bind to the active

site of the enzyme, preventing the site of the enzyme, preventing the substrate from bindingsubstrate from binding

This is reversibleThis is reversible

Competitive inhibitors usually have a Competitive inhibitors usually have a similar structure to the substrate for similar structure to the substrate for that enzyme and that enzyme and fit into the active site fit into the active site easilyeasily

Non-competitive Non-competitive inhibitorsinhibitors Non-competitive inhibitors also bind to Non-competitive inhibitors also bind to

the enzyme, but not the active sitethe enzyme, but not the active site When the inhibitor binds to the When the inhibitor binds to the

enzyme, it alters the tertiary structure enzyme, it alters the tertiary structure slightly, causing a change in the shape slightly, causing a change in the shape of the active siteof the active site

The change in the active site prevents The change in the active site prevents the substrate from binding to itthe substrate from binding to it

This is reversibleThis is reversible

ToxinsToxins

Many toxins can bind irreversibly to Many toxins can bind irreversibly to enzymes, changing the active site enzymes, changing the active site permanentlypermanently

Some examples are:Some examples are: Snake venomSnake venom Nerve gasesNerve gases Heavy metalsHeavy metals

Cofactors and coenzymesCofactors and coenzymes Some enzymes only function when another Some enzymes only function when another

chemical component is able to attach to them chemical component is able to attach to them There are 2 types of these chemical There are 2 types of these chemical

components:components: Cofactors (inorganic molecules)Cofactors (inorganic molecules) Coenzymes (organic molecules)Coenzymes (organic molecules)

These cofactors and coenzymes are usually These cofactors and coenzymes are usually carrier molecules and transfer electrons or carrier molecules and transfer electrons or ions from one molecule to another (eg. NADH, ions from one molecule to another (eg. NADH, FADH2 and NADPH)FADH2 and NADPH)