Enzymes

What is it??

• Enzymes are PROTEIN molecules.• Protein molecules are composed of one or

more amino acid chains, folded into uniquely shaped globs.

· Enzymes act as CATALYSTS! · Catalysts are chemicals that regulate the

rate of chemical reactions.· Are not consumed or altered during the

reaction

Activation Energy

· Activation Energy is the energy input required to initiate any reaction.

Activation Energy

· Activation Energy is the energy input required

to initiate any reaction.

· Enzymes regulate cell activities (metabolism)

by lowering the activation energy

· reactions, therefore, occur more rapidly and at

lower temperatures.

Activation Energy

Activation Energy

Activation Energy

FUNCTION vs. SHAPE

TWO THEORIES

1) LOCK & KEY THEORY • Each chemical reaction requires its own enzyme

therefore “one reaction = one enzyme” concept• The enzyme forms a temporary bond with a

special molecule called a SUBSTRATE • substrate a molecule on which an enzyme works

– A substrate is always… » the substance acted upon» the substance which is changing

• Active Site the area of an enzyme that combines with the substrate

Get’in Together• When the substrate and the enzyme

combine or “join” at the active site, the tandem is called an Enzyme-Substrate Complex.

Lock & Key (Con’t)

– The ENZYME-SUBSTRATE COMPLEX then separate into product(s) and enzyme

Important

• Note that:– The enzyme remains unchanged and ready to

react again with a new substrate.

Important

• The substrate has been turned into products.

INDUCED FIT MODEL• Improved Theory – 1973

– suggests that the shape of the active site does NOT exactly fit the shape of the substrate

– The substrate forces its way into the enzyme

– This makes for a tighter fit– The orientation of the substrate molecules

in the ENZYME-SUBSTRATE COMPLEX helps speed up the chemical reaction by · adding stress to bonds more easily· bringing reactive sites physically closer

together

Induced Fit (Cont’d)· Once a bond is formed (or broken) in

substrate(s) then products are released and the ENZYME REMAINS UNCHANGED and may be REUSED!· A single enzyme can catalyze several million

reactions in one minute· The same enzyme may also catalyze the reverse

reaction

· The net result is that a one step reaction is converted into a multi-step reaction, therefore, lowering the activation energy – the minimum amount of energy required to initiate a chemical reaction.

Naming Enzymes· Enzymes are named after the substrate which it acts

upon· To name an enzyme, usually, the suffix “ase” is

added to the end of the substrate name.

· For example:

Substrate Enzyme

Sucrose Sucrase

Lactose Lactase

Peptide Bonds Peptidase

-Ketoglutarate ... ?????

-Ketoglutarase

Regulation of Enzyme Activity

· METABOLIC PATHWAYS · cellular processes that involve many steps

are controlled by enzymes· one enzyme for each step.

Allosteric Activitya change in an enzyme caused by the binding of a molecule

· Some enzyme’s shape may be altered by a “moderator molecule”. · can be a cofactor (mineral) · Coenzymes (organic molecules) · sometimes even the product molecule.

A Moderator Molecule

Cofactors

Regulation of Enzyme Activity· FEEDBACK INHIBITION

· Stops a metabolic pathway· the product of an metabolic pathway

acts as a moderator on an enzyme in the series, thereby altering its shape (active site)

· the enzyme cannot combine with the substrate

· Once the moderator molecule is removed from the moderator site, the active site snaps back to its original shape.

GlucoseGlucoseGlucose

GlucoseGlucose

Feedback Inhibition

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

GlucoseGlucoseGlucose

Glucose

Glucose

Glucose

GlucoseGlucose

Glucose

feedback inhibition

• feedback inhibition the inhibition of an enzyme in a metabolic pathway by the final product of that pathway

feedback inhibition

Factors Affecting Enzyme Reactions

• There are four factors that affect the rate

at which an enzyme can work.

1) Temperature

2) pH

3) Substrate Concentration

4) Competitive Inhibitor Molecules

TEMPERATURE

in order for a reaction to occur molecules must collide

· as temperature increases, collisions increase

DOES RATE OF REACTION INCREASE WITH

TEMPERATURE???• NOT NECESSARILY!!

Enzymes have an optimal temperature at which the reaction

is fastest.· Beyond this temperature, the rate of reaction

decreases· This is because at high temperatures, the unique

shape begins to change – denaturation.· This results in a loss of the active site· Each enzyme has its own optimal temperature

· Human body approx. = 370C· Sperm producing enzymes = 340C

· This explains why fevers and colds are dangerous

pH

· acidity or alkalinity· the lower the number the more acidic· the higher the number the more alkaline· Enzymes have an optimal pH at which the

reaction is fastest· Just like with temperature, pH’s out of

the optimal range will cause a decrease in rate of reaction

· shape changes = enzyme denatures.

CONCENTRATION

· Since molecules must collide for a reaction to occur, it is only logical that the more substrates you have, the greater the chance the enzyme will have of combining and reacting with it.

· The rate does not continue to rise as you add more and more substrate.

· There is a limit to the amount of enzyme available· A substrate cannot join with the active site of an

enzyme until it is free.· Therefore, once the number of substrate molecules

exceeds the number of enzyme reaction sites, the reaction rate levels off.

Competitive Inhibitor Molecules· Competitive Inhibitor molecules interfere

with the enzyme combining with its substrate. –Competitive Inhibitor

· shaped like substrate· COMPETES for active site· fits into active site

· = physically blocks substrate from entering active site

· enzyme becomes useless

Competitive

Inhibition

Competitive Inhibitor Molecules· Examples:

· Cyanide – binds to enzyme in the Electron Transport Chain preventing formation of ATP.

· Carbon Monoxide – binds to hemoglobin irreversibly, therefore, no oxygen can be carried

· Penicillin – binds to enzyme that allows bacteria to make its protective covering, therefore, bacteria becomes susceptible to the immune system and other drugs