Enzymes: Complete Guide To Types, Functions, and Classification

Enzymes are biocatalyst that speed up the chemical reaction in living organisms.

All enzymes have a unique active site where they bind to a specific substrate and produce a specific product. The steps involved in the function of enzymes are substrate binding, formation of enzyme-substrate complex, catalysis, and release of product. Enzymes perform various activities like digestion, respiration, DNA replication, and metabolism. There are various types of enzymes in living organism such as oxidoreductases, lyases, Isomerases, ligases, etc.

In 1964, the International Union of Biochemistry (I.U.B.) classified the enzymes based on the types of reactions they catalyse. This was done for a systematic study and to avoid an unambiguous naming system for all enzymes. According to IUB, there six major types of enzymes. Due to recent development, a new class, namely "translocase".

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Classification of Enzymes

Class Name	Types of Reaction Catalyze
Oxidoreductases	Oxidation and reduction reactions
Transferases	Transfer of functional groups (methyl, amino, phosphate)
Hydrolases	Hydrolytic reactions
Lyases	Addition or removal of groups to form double bonds.
Isomerases	Transfer groups within molecules to yield isomeric forms
Ligases	Uses ATP energy to join two molecules
Translocase	Transfer ion / molecules across the membrane

Types of Enzymes

Students can check below the major types of enzymes in detail.

Oxidoreductases

• The function of oxidoreductases is to catalyse oxidation-reduction (redox) reactions, which means the transfer of electrons or hydrogen. Moreover, it is important in respiration and energy production. Examples of oxidoreductases are oxidase, dehydrogenase, and catalase.

Transferases

• These catalyze the transfer of functional groups such as amino, phosphate, or methyl from one molecule to another. Transferase is involved in metabolism and protein synthesis. Examples of transferase enzymes are kinases and transaminases.

Hydrolases

• They catalyze to breaking of large molecules into smaller ones using water (hydrolysis). Hydrolysis is crucial in digestion. Examples of hydrolases are amylase, lipase, and protease.

Lyases

• These catalyze to add or remove of groups from molecules without using water. Its role is to break bonds in metabolic pathways. For example: decarboxylase, Aldolase.

Isomerases

• The function of isomerases is to rearrange atoms in a molecule to form isomers. They are important in glycolysis and carbohydrate metabolism.

Ligases

• These catalyze by joining two molecules together, using ATP energy. It is essential in DNA replication and repair. Some important examples of ligases are DNA ligase, carboxylase.

Trick to Remember the Classification of Enzymes

"oh, The Hot Lovely Ice Lemon"

O - Oxidoreductases

T - Transferases

H - Hydrolases

L - Lyases

I - Isomerases

L – Ligases

 For a better understanding of enzymes structure and functions, we have explained them below in detail.

Structure of Enzymes

1. Protein Nature
2. Active Site
3. Substrate
4. Enzymes-Substrate complex
5. Cofactors and Coenzymes
6. Denaturation

Protein Nature

Enzymes are globular proteins. It is made up of long chains of amino acids folded into 3D shapes.

Active Site

These are the regions where enzymes bind to a specific substrate.

Substrate

These are the molecules on which enzymes act.

Enzymes-Substrate Complex

This is a temporary structure that is formed when the substrate fits into the active site.

Cofactors and Coenzymes

Some enzymes require non-protein components for proper function. These components are classified as cofactors and coenzymes.

Denaturation

Certain factors, like high temperature, extreme pH, or chemicals, can affect the enzyme's structure and make it inactive.

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Functions of Various Enzymes

Enzymes are responsible to speed up chemical reaction in living organism. There are various enzymes with different functionality. Below are the function of some enzymes. 

1. Amylase: This is a group of enzymes that is present in the saliva and pancreases. It helps to break down starch into simple sugars like maltose.
2. ATP Synthase: This enzyme produces ATP during the cellular respiration. It is available in mitochondria.
3. DNA Polymerase: When cell break or split it form new cell. DNA polymerase help to copy the DNA during the cell division. This enzymes is found in nucleus of cells.
4. Carbonic Anhydrase: It is an important enzymes produced in liver cell and many tissues. It breaks hydrogen peroxide into water and oxygen.

Enzymes are biological catalysts that are used to speed up chemical reactions in living organisms. It is one of the important components for the proper functioning organism. Here we have the mechanism of enzyme action. We explain this using the "lock and key model" and the induced fit model. Let's discuss them:

Substrate Binding

• Enzymes bind to a specific substrate at a region known as the active site and act on it without being used. These bindings are highly specific.

Formation of Enzyme-Substrate Complex

• When enzymes bind to substrate, they form a temporary enzyme-substrate complex. This lowers the activation energy required to start the reaction.

Catalysis

• The enzymes catalyze the substrate's bond by breaking it down or joining it together.

Release of Products

• After the completion of the reaction, the enzyme releases the product without being unchanged and is ready for reuse.

Enzymes Ready for Next Reaction

• After the reaction, the enzyme returns to its original shape and is ready to bind with a new substrate molecule for catalysis.

In short: Enzymes work like a machine, grab the write molecules, begin the process (reaction), release the product while staying unchanged themselves.

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Enzyme catalysis is influenced by changing environmental conditions. The factors that affect the enzymes' activities are temperature, pH, substrate concentration, and modulators.

Temperature

Enzymes catalyze best at the optimum temperature (normal body temperature). It gets affected when there are changes in the temperature. Suppose the temperature is high, it will break down the enzyme's structure (denaturation), resulting in no functions. In the case of low temperature, enzyme activities are slow due to the slow movement of molecules.

pH Level

Each enzyme has a suitable pH level to perform best. An increase in acidic or alkaline pH changes the shape of enzymes, resulting in reduced activity. For example, Pepsin (in the stomach) performs best in acidic conditions, while amylase works best when the pH is neutral.

Substrate Concentration

The reaction is fast if the number of substrates is increased. If the enzyme's active site is filled, the rate of reaction will not increase further; this is its saturation point.

Enzymes Concentration

The rate of reaction increases by increasing the enzyme concentration only if the substrate is present. In case substrates are limited, then there is no benefit of adding more enzymes.

The rate of reaction that is catalyzed by enzymes is called enzyme kinetics. It helps us to understand the functioning of enzymes, the rate of converting substrates into products, and the factors influencing their activities. You can check below for detailed information on enzyme kinetics. 

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Key Concepts in Enzyme Kinetics 

Here you can check the key concept of enzyme kinetics in detail.

Substrate and Products 

1. Substrate: These are the molecules upon which enzymes act.
2. Products: When enzymes complete the catalytic reaction, the molecule formed is called a product.

Rate of Reaction 

This is the speed at which substrate is converted into product. 

It is measured as the change in concentration of substrate or product over time. 

Michaelis-Menten Equation 

This is the formula for enzyme kinetics

$v=\frac{V_{\mathrm{m}\mathrm{a}\mathrm{x}}\left[S\right]}{K_m+\left[S\right]}$

where:

• $v$ : Initial reaction velocity
• $V_{\text{max}}$ : Maximum velocity when the enzyme is saturated
• $\left[S\right]$ : Substrate concentration
• $K_m$ : Michaelis constant, indicating substrate affinity (lower $K_m$  means higher affinity)

This relationship is graphically represented in the Lineweaver-Burk plot.

These are the molecules that are responsible for reducing the enzymes' activities, either by blocking the active site or changing the shape of the enzymes. There are three types of enzyme inhibition-competitive, Non-competitive and uncompetitive.

Competitive

This inhibitor competes with the substrate for the enzyme's active site.

Non-Competitive

They bind to the site other than the active site. This causes a change in the enzymes shape and reduces its efficiency.

 Uncompetitive

These inhibitors bind only to the enzymes-substrate complex.

Why is Enzyme Kinetics Important?

Enzyme kinetics are important because they are useful in the development of drugs, biotechnology, and the diagnosis of diseases.