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What you will learn• Examine enzymatic pathways, • Focus on how they inhibit or activate reactions• Use appropriate terminology related to

biochemistry e.g. allosteric, substrate, substrate-enzyme complex, inhibition

• Describe the chemical structures and mechanisms of various enzymes

• Analyse technology applications related to enzyme activity in the food and pharmaceutical industries

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Enzymes

• They are proteins that catalyze reactions• They are required for all metabolic activities,

so reactants are converted into products faster.

• The catalysts are not consumed in the process, so they can be recycled for other reactions

• Most enzymes ends with “ase”• They are denatured by high temperature

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Enzymes

• For chemical reactions to occur:• An activation energy(EA) barrier must be

overcome• Heat provides the activation energy for most

reactions• catalysts help to overcome activation energy

(EA), and allow reactions to occur at lower temperatures

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Exergonic Reaction Endergonic Reaction

Reactions with and without a Catalyst

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Enzymatic Pathway• In enzyme catalyzed reaction, the substrate binds

to the part of the enzyme called the active site• the active site is a 3-D pocket that matches the

shape of the substrate in order for binding to occur.

• Interactions between functional groups on the enzyme and substrate cause the protein to change shape as the substrate enters the active site in a process called Induced-fit model

• when substrate is bound to the enzyme, the bond is called enzyme-substrate complex

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Enzymatic Hydrolysis of Sucrose

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Factors Affecting Enzyme Activity

• Temperature• pH value• Concentration of substrate• Concentration of the enzyme itself

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Temperature

• As temperature rises, reacting molecules gain more energy and more kinetic energy,

• This increases the chances of a successful collision,• Which causes the rate of enzymatic reaction to

increase as well• Every enzyme has a specific or optimal temp. where

its activity is the greatest. E.g. body enzymes has optimal temp. 37.5oC

• At higher temp. intra and intermolecular bonds are broken as enzymes gain more kinetic energy, they become denatured.

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pH• Each enzyme works within quite a small pH

range.• Activities are greatest at optimal pH• Changes in pH break intra- and intermolecular

bonds, changing the shape of the enzyme, and effectiveness.

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Effect of Temperature and pH on Enzyme Activity

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Concentration of enzyme and substrate• As concentration of either is increased the rate of

reaction increases (see graphs).• Rate of reaction increases with increasing substrate

concentration up to a point,• Above which any further increase in substrate

concentration produces no significant change in reaction rate.

• Why? – because the active sites of the enzymes molecules at any given moment are virtually saturated with substrate.

• Enzyme/substrate complex has to dissociate before the active sites are free to accommodate more substrate

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Concentration of enzyme and substrate

• Provided that the substrate concentration is high and that temperature and pH are kept constant, the rate of reaction is proportional to the enzyme concentration.

• Enzymes inhibitors are molecules that bind to enzymes and decrease their activity

• Enzymes activators bind to enzymes and increase enzymatic activity.

• Many drugs are enzyme inhibitors, because blocking an enzyme’s activity can kill a pathogen or correct a metabolic imbalance.

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Inhibition of Enzyme Pathway• To understand how inhibition works, the

structure of an enzymes must be examined.• Substances bind to enzymes in two locations

– Active site: this is a big pocket or cleft surrounded by amino acids and other side chains that contain residues responsible for allowing specific substrates to bind

– The allosteric site: this is a location other than the active site, this binding can either activate or inactivate an enzymatic pathway.

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Enzyme

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How enzymes Work

• Two proposed models:– Lock-and-key model: this assumes that the active site

is a perfect fit for a specific substrate (once the substrate binds there is no further modification)

– Induced fit model: developed from the lock and key model, conformational change may occur in the enzymes as it binds to the substrate. It assumes that an active site is more flexible, that amino acids located in the active site encourages the enzymes to locate the correct substrate

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Competitive Inhibition

• Inhibitor is similar to regular substrate• It is able to enter the enzyme’s active site• The binding of the inhibitor can stop a substrate

from entering the enzyme’s active site and stop the enzyme from catalyzing its reaction,

• The process can also be reversed, by increasing the amount of the enzyme’s regular substrate.

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Competitive Inhibition

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Non-Competitive Inhibition

• Inhibitor does not compete for the enzyme’s active site,

• It binds to the enzyme’s allosteric site• Which causes a change in the enzyme’s shape

preventing it from binding to its regular substrate.

• If binding and reduction of enzyme is permanent, then the substance binding to the enzyme is considered a toxin

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Non-competitive Inhibition

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• Inhibitor binding can be either reversible or irreversible.

• Irreversible inhibitors modify key amino acid residues needed for enzymatic activity

• Reversible inhibitors bind non-covalently and different types of inhibition are produced on whether these inhibitors bind the enzyme, the enzyme-substrate complex, or both

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Allosteric Regulation: Activators and Inhibitors

• Cells control enzymatic pathways to coordinate cellular activities.– Molecules that promote the action of enzymes can

bind to the allosteric site of an enzyme. These molecules are known as activators

– Percursor activation is when an accumulation of a substance within a cell activates an enzyme by binding to its allosteric site and setting in motion new sequence of reactions.

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Feedback Inhibition

• This is a type of non-competitive inhibition in which the end product of a series of enzymatic reactions binds at an allosteric site on the first enzyme of the pathway

• This way a cell is able to maintain “homeostasis” or internal balance

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Feedback Inhibition

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Feedback Inhibition and Precursor Activity

• Activity of the enzyme is being regulated by a molecule which is not its substrate.

• In these cases the regulator molecule binds to the enzyme at a different site than the one to which the substrate binds.

• This create allosteric effect because its (enzyme) shape is changed.

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Allosteric Regulation

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Use of Enzymes

• Includes industrial and commercial purposes– E.g. proteases are used in the dairy industry to

produce cheese– proteases, along with amylase, are also added to

detergents to help remove protein and carbohydrate produced stains

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Co-enzymes• Coenzymes are cofactors which are inorganic molecules

that bind to enzymes and serve as carriers for chemical groups or electrons.

• E.g. are NAD+ and FAD are coenzymes involved in cellular respiration

• Many coenzymes are dependent on the intake of Vitamins

• E.g. NAD+ is dependent on niacin and FAD on riboflavin• A deficiency in one of these vitamins may result in a

lack of a coenzyme, and therefore a decrease in certain enzymatic reactions

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http://www.youtube.com/watch?v=5eBzLgleVL8&feature=related

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Unit 1- Test

• To be given– Multiple choice– Short answers– Application questions