ENZYMES

Action, Inhibition and its Importance

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DEFINITION

• Enzymes are proteins that help and speed up metabolism, or the chemical reactions in our bodies.
• They build some substances and break others down.
• All living things have enzymes.
• Our bodies naturally produce enzymes. But enzymes are also in manufactured products and food.
• Exaples : Amylase (in mouth and pancreas; breaks carbohydrates),Lipase (in pancreas; breaks down fats), Protease (in pancreas; breaks down proteins)

Models

ACTIVE SITE

• The part of the enzyme where the substrate binds is called the active site (since that's where the catalytic “action” happens).
• A substrate enters the active site of the enzyme. This forms the enzyme-substrate complex.
• Then the required product or functions are made.
• There are two main models of enzyme action: Lock and Key model and Induced Fit model.

Lock and Key model

• The Lock and Key model of enzyme action is described because it explains that a substrate will fit a specific enzyme, similar to how a key fits a specific lock.
• Emil Fischer first proposed the Lock and Key model of enzyme action in 1899.
• The active site of an enzyme is structured to fit a specifically shaped substrate.
• Once the substrate binds to the active site, the enzyme will facilitate the reaction and release products of the reaction.

Induced Fit model

• According to the induced fit model, the enzyme’s active site is not a completely rigid fit for the substrate.
• Instead, the active site will undergo a conformational change when exposed to a substrate to improve binding.
• This theory of enzyme-substrate interactions has two advantages compared to the lock and key model:

1. It explains how enzymes may exhibit broad specificity (e.g. lipase can bind to a variety of lipids)

2. It explains how catalysis may occur (the conformational change, stresses bonds in the substrate, increasing reactivity).

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ENZYME INHIBITIONS

• An enzyme inhibitor is a substance that prevents an enzyme from reacting with its substrate. This process is known as enzyme inhibition.

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• There are three main types of inhibition

1.Competitive,

2.Noncompetitive, and

3.Uncompetitive  

COMPETITIVE INHIBITION

• A competitive inhibitor is any compound that bears a structural resemblance to a particular substrate.
•  Thus competes with that substrate for binding at the active site of an enzyme.
• The inhibitor is not acted on by the enzyme but does prevent the substrate from approaching the active site.
• If the inhibitor is present in relatively large quantities, it will initially block most of the active sites. 
• By increasing the substrate concentration promotes displacement of the inhibitor from the active site.

NONCOMPETITIVE INHIBITION

• A noncompetitive inhibitor attaches at an allosteric site (another site of enzyme), which is any site on the enzyme that is not the active site.
• The attachment of the non-competitive inhibitor to the allosteric site results in a shift in three-dimensional structure that alters the shape of the active site so that the substrate will no longer fit in the active site properly.
•  A noncompetitive inhibitor can combine with either the free enzyme or the enzyme-substrate complex.  

UNCOMPETITIVE INHIBITION

• Uncompetitive inhibition occurs when an inhibitor binds to an allosteric site of a enzyme, but only when the substrate is already bound to the active site.
• In other words, an uncompetitive inhibitor can only bind to the enzyme-substrate complex.
• It makes it incredibly difficult for the substrate to become unbound from the enzyme. 
• However, the binding of the inhibitor affects the binding of the substrate, and vice-versa. This type of inhibition cannot be overcome, but can be reduced by increasing the concentrations of substrate.

ENZYME KINETICS

• Enzyme kinetics is the study of the rates of enzyme-catalysed chemical reactions.
• Enzymes are protein catalysts that accelerate the rates at which reactions approach equilibrium.

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MM EQUATION

• The Michaelis-Menten model (1) is the one of the simplest and best-known approaches to enzyme kinetics.
• It takes the form of an equation relating reaction velocity to substrate concentration for a system where a substrate S binds reversibly to an enzyme E to form an enzyme-substrate complex ES, which then reacts irreversibly to generate a product P and to regenerate the free enzyme E.
• This system can be represented schematically as follows:
• The Michaelis-Menten equation for this system is:

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IMPORTANCES OF ENZYMES

THANK YOU

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BY

M.JERLINE

Head and Assistant Professor

Department of Biochemistry

Dr.R.A.N.M Arts and Science College,Erode.