What are Enzymes in a cell? Functions, Examples and Types

Table of Contents

What Are Enzymes?

Enzymes in a cell are simply biopolymers (large units derived from smaller units in living things) that catalyze biochemical reactions. The majority of enzymes are proteins with catalytic capabilities that are required to carry out various processes. A set of enzymes are required for life functions, especially in carrying out metabolic processes and other chemical reactions in the cell.  All enzymes have protein as their macromolecular component, with the exception of ribozymes, which are RNA catalysts.

Enzymes are observed in all of the tissues in the body and fluids. Intracellular enzymes catalyze all of the reactions that take place in metabolic pathways. Enzymes in the plasma membrane control catalysis in cells in response to cellular signals, while enzymes in the circulatory system control blood clotting.

Functions of enzymes

  1. They aid in signal transduction such as protein kinase, which catalyzes the phosphorylation of proteins, which is the most common enzyme used in the process.
  2. They tear larger molecules into smaller molecules so that the body can easily absorb them.
  3. They aid in the production of energy in the body such as ATP synthase which is responsible for energy synthesis.
  4. The movement of ions across the plasma membrane is controlled by enzymes.
  5. They carry out a variety of biochemical reactions such as oxidation, reduction, hydrolysis, and others in order to eliminate non-nutritive substances from the body
  6. Enzymes are responsible for reorganizing the cell’s internal structure in order to regulate cellular activities.
  7. They catalyze food and household products. For example beverages, yogurt, and bread.

What are enzymes made of?

Enzymes are made up of a three-dimensional structure that is composed of a linear chain of amino acids. In simple terms, they are made of long chains of amino acids.

Some enzymes are composed of a single chain of amino acids, whereas others are composed of multiple chains of amino acids. Every enzyme is made up of a distinct chain of amino acids (i.e., no two enzymes have the same amino acid structure), and each enzyme has its own distinct shape.

They are typically large in comparison to their substrates, with sizes ranging from 62 amino acid residues to an average of 2500 residues in fatty acid synthase. Just a small portion of the structure, close to the binding sites, is engaged in catalysis.

How do enzymes work?

Enzymes work by playing a crucial role in lowering the activation energy of a reaction, that is, the amount of energy required to start the reaction.diagram of an enzyme

They also work in binding to reactant molecules and holding them in a position that allows chemical bond-breaking and bond-forming to occur more quickly. In simple terms, enzymes work by aiding in the acceleration of chemical reactions in the human body. They bind to molecules and cause them to change in specific ways.

To explain another point, enzymes do not change the delta G value of a reaction. That is, they have no effect on whether a reaction is overall energy-releasing or energy-absorbing.

This is due to the fact that enzymes have no effect on the free energy of the reactants or products.
Instead, enzymes reduce the energy of the transition state, which is an unstable state through which products must pass in order to become reactants.

Enzymes can also work as biological catalysts. (A biological catalyst, is an example of a catalyst that remains unchanged in terms of quantity and chemical properties during a chemical reaction). Enzymes found in living organisms speed up the rate of chemical reactions within the body.

They do so when substrate molecules attach themselves to an enzyme’s active site (the location of an enzyme where substrate molecules attach to await chemical reaction).

At first, substrates bind to enzymes through noncovalent interactions such as ionic, hydrogen bonds, and hydrophobic interactions. Then they reduce the reaction time and activation energy, allowing them to reach equilibrium faster than non-catalyzed reactions.

Allosteric regulation (Allosteric regulation is the process of modulating the behavior of a protein by attaching a ligand, known as an effector, to a site topographically different from the site of the protein, where the activity characterizing the protein is conducted, whether catalytic in the case of enzymes or binding in the case of receptors) is used by both eukaryotic and prokaryotic cells to respond to changes in their internal state.

Examples of enzymes

  • Lipases are a group of enzymes that aid in the digestion of fats in the intestine.
  • Amylase aids in the conversion of starches to sugars and it is found in saliva.
  • Maltase is a sugar that breaks down maltose into glucose and is found in saliva.
  • Maltose can be found in a variety of foods, including potatoes, pasta, and beer.
  • Proteins are broken down into amino acids by trypsin, which is found in the small intestine.
  • Lactase is a digestive enzyme that breaks down lactose, the sugar in milk, into glucose and galactose. Identified to be in the small intestine.
  • Acetylcholinesterase – in nerves and muscles, this enzyme breaks down the neurotransmitter acetylcholine.
  • Helicase is a DNA unraveling enzyme.
  • DNA polymerase is an enzyme that converts deoxyribonucleotides into DNA
  • Pectinase enzymes break down foods that are rich in pectin. For example, citrus fruits, apples, carrots, potatoes, beets, and tomatoes.
  • Bromelain functions by hydrolyzing food protein into smaller peptones; aids the body’s fight against cancer improves circulation and treats inflammation.
  • Papain helps in the digestion process in the body.
  • Catalase breakdown and converts hydrogen peroxide into water and oxygen. It is essential for immune function.


  1.  They increase the rate of chemical reactions.
  2. They are only needed in trace amounts.
  3. They act in a very specific manner.
  4. They affected by temperature
  5. pH has an effect on their function
  6. Some have the capability to catalyze reversible reactions.
  7. Some require the help of coenzymes to function effectively.
  8. The presence of Inhibitors prevents them from functioning.

Types of enzymes

They are classified into 6 functional classes, as per the International Union of Biochemists (I U B), and are classified based on the type of reaction they catalyze namely;

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

The classification and the names of enzymes based on type, biochemical properties, substance they catalyze, and examples are described in the table below.

  Types and examples of enzymes
Names of enzymes
Biochemical properties
Substance they catalyze
The oxidation reaction in which electrons tend to travel from one form of a molecule to the other is catalyzed by the enzyme Oxidoreductase.
They catalyze oxidation and reduction reactions
Pyruvate dehydrogenase, which catalyzes pyruvate to acetyl coenzyme A oxidation.
Hydrolases are hydrolytic enzymes that catalyze the hydrolysis reaction by cleaving and hydrolyzing the bond by adding water.
The hydrolysis of a bond is catalyzed by them.
Pepsin, for example, breaks down peptide bonds in proteins.
Transferases aid in the transportation of functional groups between acceptors and donors.
They catalyze the transfer of a chemical group from one compound to another.
A transaminase, for example, is an enzyme that transfers an amino group from one molecule to another.
Water, carbon dioxide, or ammonia is added across double bonds to create double bonds, or it is removed to create double bonds.
These break bonds without catalysis.
For example, aldolase (a glycolysis enzyme) functions by catalyzing the conversion of fructose-1, 6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Ligases are known to be involved in the catalysis of ligation reactions.
They catalyze the joining of two molecules.
DNA ligase, for example, catalyzes the formation of a phosphodiester bond between two DNA fragments.
Isomerase catalyzes structural shifts in a molecule, resulting in a change in the shape of the molecule.
They catalyze the formation of a compound’s isomer.
In glycogenolysis, phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate (where the phosphate group is transferred from one position to another in the same compound) (glycogen is converted to glucose for energy to be released quickly).

Enzymes cofactors

They are non-proteinous substances that associate with enzymes to aid the function of the enzymes. An enzyme’s function is dependent on the presence of a cofactor. Apoenzymes are enzymes that do not require a cofactor. The holoenzyme is made up of an enzyme and its cofactor.

In enzymes, there are three types of cofactors:

  1. Prosthetic groups: Are cofactors that are always tightly bound to an enzyme.
  2. Coenzyme: During catalysis, a coenzyme binds to an enzyme. It is detached from the enzyme at all other times. NAD+ is a widely used coenzyme during catalysis.
  3. Metal ions: Certain enzymes require a metal ion at the active site to form coordinate bonds during catalysis. A number of enzymes use the metal ion cofactor Zn2+ to accomplish their goal.


  • Enzymes are necessary for a healthy digestive system as well as a healthy body.
  • They collaborate with other body chemicals like stomach acid and bile to break down food into molecules for a variety of bodily functions. Carbohydrates, for example, are required for energy, while protein is required for muscle growth and repair, among other things. However, they must be converted into forms that your body can absorb and use.
  • Due to their importance in maintaining life processes, enzyme regulation has long been a key component in clinical diagnoses, such as elevated liver enzymes detected in blood in liver function tests shows ongoing liver cells.
  • They are used in the food industry especially in the production of fermented products such as yogurt and alcohol.

Factors affecting enzymes activity

  • Salt concentration
  • Concentration and type of substrate
  • Temperature
  • pH
  • Active site