Enzymes 101: What They Are and How Do They Work?

by Mahrukh Husain

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Confused about what exactly are enzymes and what they do, especially in terms of O Level and IGCSE Biology? In this article, we will explore the definition of enzymes and take a look at the important role they play in keeping us healthy. 


Table of Contents:


What enzymes do, what are the ways they function, their classification and so many more O Level & IGCSE Biology concepts are available at Out-Class.


What Are Enzymes?

Enzymes can be described as: 

Biological catalysts that speed up the rate of a chemical reaction without being consumed or changed in the process.


In simple terms, enzymes are tiny biological machines that help speed up important chemical reactions related to breaking down food for energy or repairing tissues. These are the building blocks required to help your body function normally and for you to stay healthy. 

With that definition, it is no wonder then why enzymes are deemed so significant. They are considered necessary for all living organisms as they facilitate various metabolic reactions within them, that too, at a rate that can sustain life. An example can be found in digestive enzymes; in their absence, it would take us up to two to three weeks to digest one single meal. With enzymes, it just takes four hours. 


Enzymes in O Level & IGCSE Biology are easily explained as to what they do, how they do and their classifications.


What Do Enzymes Do?

Enzymes work by binding to specific molecules (also known as substrates) and converting them into different molecules (also known as products). Each enzyme has been given a specific job so whenever a molecule needs to undergo a chemical change, it goes to the enzyme that is specialized in that particular job. 

The area within the enzyme that binds with a molecule or substrate is called the active site. These have specific shapes that allow them to recognize and then connect with the substrate molecules, much like a key to a lock. Once the molecule is in place, the enzyme helps speed up the reaction, thereby making it easier for the molecule to change into its final form (the product). 

Once the reaction is complete, the product exits the enzyme which then prepares to bind with other substrates. One of the key strengths of enzymes is that they can continue to bind with molecules and speed up their chemical reactions without getting used up. 


it shows how do enzymes work

Enzymes and the Chemical Reaction Process


What Are Enzymes Made Of?

Polypeptide Chains

Enzymes are a type of protein and are made up of one or more amino acid chains called polypeptide chains. Amino acids can be described as a group of organic molecules that are composed of several subgroups. These include: 

  • A basic amino group (-NH2) 

  • An acidic carboxyl group (-COOH) 

  • An organic R group (or side chain) 

These provide the foundations for proteins and enzymes along with the strength to carry out their functions. They are also responsible for the folding patterns found within enzymes; this helps them bind with certain molecules and perform their specific functions. 



Another chemical component found within enzymes is an additional chemical component called a cofactor. This plays a direct role in the chemical reaction and is thus essential to the genetic makeup of the enzyme. There are three different cofactors present within enzymes. These include: 

  • Prosthetic Groups: These types of cofactors can be found tightly bound to an enzyme at all times. Examples include flavin adenine dinucleotide (FAD).

  • Coenzyme: This type of cofactor only binds with an enzyme during the process of catalysis. Examples include NAD.

  • Metal ions: This can be found at the active site of the enzyme. This helps in the catalysis process of the chemical reaction and also helps to form coordinate bonds between the enzyme and the molecule. Examples include zinc. 


Classification of Enzymes


There are six kinds of enzymes, each classified in accordance with the type of reaction they are meant to process: Oxidoreductases, Hydrolases, Transferases, Isomerases, Ligases or Synthetases & Lyases.


There are six kinds of enzymes, each classified under the type of reaction they are meant to process. These include the following:

  • Oxidoreductases: These enzymes catalyze oxidation-reduction reactions which involve the transfer of electrons between molecules.

  • Hydrolases: These enzymes catalyze hydrolysis reactions; this is where a molecule is broken down into smaller parts by adding water.

  • Transferases: These enzymes catalyze the transfer of functional groups, such as methyl or phosphate groups, from one molecule to another.

  • Isomerases: These enzymes catalyze the rearrangement of atoms within a molecule to form isomers, which are molecules with the same chemical formula but different structural arrangements. 

  • Ligases or Synthetases: These enzymes catalyze the joining of two molecules, usually coupled with the hydrolysis of ATP or another high-energy molecule. 

  • Lyases: These enzymes catalyze the addition or removal of a group from a molecule without hydrolysis. 


Types of enzymes and their classifications as per their functions exist in IGCSE Biology and O Level Biology.


Types of Enzymes

According to Medical News Today, there are currently thousands of enzymes present within the human body that perform around 5000 different functions regularly. Let’s take a look at some examples of these enzymes:

  • Lipases: This group of enzymes help to digest fats within the gut

  • Amylase: This particular type of enzyme can be found in our saliva. It helps to change starches into sugars. 

  • Maltase: This also exists in our saliva and is responsible for breaking down sugar maltose into glucose.

  • Trypsin: These enzymes break down proteins into amino acids for the small intestine.

  • Lactase: This helps break down lactose (the sugar found within milk) into glucose and galactose.

  • Acetylcholinesterase: These enzymes break down the neurotransmitter acetylcholine in nerves and muscles.

  • Helicase: These enzymes help to unravel DNA.

  • DNA polymerase: These enzymes synthesize DNA from deoxyribonucleotides. 



Overall, enzymes play a crucial role in virtually all biochemical processes, including digestion and metabolism, DNA replication and cellular signalling. Their ability to catalyze specific reactions with remarkable efficiency makes them indispensable for life. If you want to learn more about enzymes, then head on to www.out-class.org and sign up today!



Q. What are enzymes and what role do they play in the body?

Enzymes are biological catalysts that speed up chemical reactions without being consumed. They play a vital role in various metabolic processes, including digestion, metabolism, DNA replication, and cellular signalling.


Q. What are enzymes made of?

Enzymes are proteins made up of one or more amino acid chains (polypeptide chains). Amino acids, the building blocks of proteins, contribute to the folding patterns of enzymes. Enzymes may also contain cofactors like prosthetic groups, coenzymes, or metal ions.


Q. How do enzymes function in chemical reactions?

Enzymes work by binding to specific molecules (substrates) at their active sites, facilitating the conversion of substrates into products. They accelerate reactions without being used up in the process.


Q. What is the classification of enzymes based on their functions?

Enzymes are classified into six categories based on their functions:

  1. Oxidoreductases
  2. Hydrolases
  3. Transferases
  4. Isomerases
  5. Ligases or Synthetases
  6. Lyases

Each category catalyzes a specific type of reaction.


Q. Can you provide examples of enzymes and their functions in the body?

Examples of enzymes include Lipases (digesting fats), Amylase (changing starches into sugars), Maltase (breaking down sugar maltose), Trypsin (breaking down proteins), Lactase (breaking down lactose in milk), Acetylcholinesterase (breaking down acetylcholine), Helicase (unravelling DNA), and DNA polymerase (synthesizing DNA).


Q. What is the significance of enzymes in digestion?

Digestive enzymes, like lipases, amylase, maltase, trypsin, and lactase, play a crucial role in breaking down food components into absorbable nutrients during digestion.


Q. Why are enzymes considered essential for life?

Enzymes are essential for life as they catalyze specific reactions with remarkable efficiency, ensuring vital processes like digestion, metabolism, and DNA replication occur at rates sustaining life.


Q. What is the lock and key model of enzyme action?

The lock and key model is a hypothesis explaining how enzymes interact with substrates. It compares the specificity of enzyme-substrate interactions to a lock that only opens with the correct key. In this model, enzymes (locks) have specific active sites that perfectly fit their substrates (keys).

Related: Lock and Key Model of Enzyme


Q. How can I learn more about enzymes for IGCSE or O Level Biology?

To deepen your understanding of enzymes and excel in IGCSE/O Level Biology, you can sign up for the course at www.out-class.org.


Q. How many functions do enzymes perform in the human body?

There are thousands of enzymes in the human body, performing approximately 5000 different functions regularly.

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