ENZYMES - Complete Study Guide

INTRODUCTION

What are enzymes?

All living organisms (plants, animals, microorganisms) need energy to perform life activities
Life activities include: Growth → Development → Locomotion
This energy comes from food through the process of metabolism

METABOLISM

Definition: All the chemical reactions which are done inside the cell

Two Types of Metabolism:

1. CATABOLISM

Complex → Simple
Example: Respiration

2. ANABOLISM

Simple → Complex
Example: Photosynthesis

NOTE: Enzymes speed up or accelerate these chemical reactions for life activities

ENZYME DEFINITION

Enzyme: Biological catalyst which speed up or accelerate chemical reaction inside the living system

Etymology (Word Origin)

Greek word: “Put available”
En- means = Inside
Zyme means = Yeast
This name is based on discovery

DISCOVERY OF ENZYMES

Historical Timeline:

1833 – Anselme Payen:

First time discovered enzyme in the process of diastases
Starch → Glucose conversion

Louis Pasteur (Bacteriologist):

During fermentation: Sugar → Alcohol
This process occurs with the help of yeast
Yeast (vital forces are present) ↓
Ferment (enzyme)

NOTE: First time discovered by Louis Pasteur

1877 – Kuhne:

The name ferment was converted into enzyme

1897 – Buchner:

Enzyme was first extracted from zymase

STRUCTURE OF ENZYMES

Two Main Parts:

1. ALLOSTERIC SITE

Largest part
Gives shape to enzyme

2. ACTIVE SITE

Functional part
Three dimensional
Smallest part
Every enzyme has specific active site
Enzymes are specific in nature
Contains 2-12 amino acid charge

Components of Active Site:

A. BINDING SITE

Attachment of substrate
Recognition of substrate

B. CATALYTIC SITE

It provides energy to activate substrate during reaction

CHARACTERISTICS OF ENZYMES

1. Biological Catalyst

Speed up chemical reaction in living system

2. Chemical Nature

All enzymes are protein in nature
Mostly tertiary protein
Exception: Ribozyme

3. Specific in Function

Each enzyme is specific
Specific function means specific enzyme speed up specific chemical reaction
Because of specific active site

Examples:

Carbohydrate digestion → Amylase
Protein digestion → Pepsin
Lipid digestion → Lipase

4. Used in Less Amount

Enzymes are used in less amount during chemical reaction

Example: A + B → C + D

5. Remain Unchanged

Enzymes are not used during chemical reaction
E + S → ES → E + P
Enzyme + Substrate → Enzyme-Substrate complex → Enzyme + Product

6. Reduce Activation Energy

Enzyme reduces activation energy during chemical reaction

Definitions:

Activation Energy: Energy required to start a chemical reaction

MODE OF ENZYME ACTION

How enzymes speed up a reaction:

General Reaction:

Without enzyme: A + B → C + D (30 minutes) With enzyme: A + B → C + D (3 minutes)

Reasons for Speed:

1. Reduce Activation Energy

In chemical reaction for the formation of new substance
Old bond break → New bond form

Example: H₂O + O₂ → H₂O

H—H + O → O
Old bond + Reduce energy → New bond form
Break → Energy → Form

Rate of chemical reaction:

Without enzyme: R → P (30 min)
With enzyme: R → P (3 min)

2. More Active Sites

Each enzyme has more than 1000s of active sites

Chemical Reaction:

Without enzyme: Complete in 30 minutes
With enzyme: Complete in 3 minutes

NOTE: Different models explain the mode of enzyme action:

Lock and Key Model
Induced Fit Model
These models explain the activity of an enzyme

LOCK AND KEY MODEL

Background:

This model was presented by Emil Fischer in 1890
Shows relationship between active site and substrate

Key Points:

Active site is complementary to substrate
Like lock and key mechanism
Substrate fits perfectly into active site
Forms enzyme-substrate complex
Products are released
Enzyme remains unchanged

FACTORS AFFECTING ENZYME ACTIVITY

1. TEMPERATURE

Low Temperature (Below 30°C)

At this temperature the bonds are very condensed
At 30°C enzyme are inactive
Small amount substrate cannot fit exactly
At 30°C enzyme become non-specific

High Temperature (Above 40°C)

Types:

High: Substrate → Product
Optimum: At 40°C the bond becomes flexible and enzyme denatures
At 30°C the rate of reaction increases
At 40°C the enzyme becomes non-specific

Optimum Temperature (37°C)

Rate of reaction is maximum
S—P (Substrate to Product conversion)

2. pH (Power of Hydrogen Ion)

For Normal Function of Enzyme:

Need specific pH
At this pH enzyme shows maximum work
Any fluctuation in normal function of enzyme will affect

Reason:

All enzymes are globular proteins and are sensitive to pH