Enzymes are proteins that aid in accelerating our bodies' chemical reactions or metabolism. Some compounds are created, while others are broken down. Enzymes are a part of all living things. Enzymes are created by our bodies spontaneously by lowering the threshold of the target reaction. They achieve this by adhering to a substrate, a different material.

Intracellular Enzymes

Enzymes found inside the cell membrane is referred to as intracellular enzymes. The cytoplasmic fluid of the cell may contain intracellular enzymes unbound or bound to specific organelles, such as ribosomes. The cell's membrane-bound organelles, such as the mitochondria, lysosomes and nucleus, also contain enzymes.

Cytoplasmic Enzyme

The fluid found inside the cell membrane is called cytoplasm. The cytoplasm of the cell contains all the cell's organelles. The primary centre of cellular metabolism is the cytoplasm. The enzyme that catalyses important metabolic processes within the cytoplasm is

Glycolysis is an anaerobic reaction in which one molecule of glucose is broken down into 2 molecules of Pyruvic acid. The conversion of glucose into pyruvic acid involves various intracellular enzymes such as Hexokinase, Phosphoglucose Isomerase, Phosphofructokinase (PFK), Aldolase, Isomerase, Triosephosphate dehydrogenase, Phosphoglycerokinase, Mutase, Enolase and Pyruvate kinase.
Gluconeogenesis is a process where glucose is synthesised from a non-carbohydrate source. The enzymes involved are Malate dehydrogenase (cytoplasmic), PEP carboxykinase, Fructose 1,6- bisphosphatase and Glucose 6-phosphatase, along with enzymes involved with glycolysis.
UDP-glucose phosphorylase, Glycogen synthase, Glycogenin, branching enzymes, Glycogen phosphorylase and Debranching enzymes are used during Glycogen metabolism, which is involved in the synthesis and degradation of glycogen.
Argininosuccinate Synthetase, Arginosuccinase and Arginase are the enzymes involved in the urea cycle.
Aspartate transaminase, alanine transaminase, glutamate dehydrogenase, arginase, serine dehydratase, tyrosine transaminase, glutamine synthetase, glutaminase and adenylate deaminase are some of the enzymes involved in amino acid metabolism.

Mitochondrial Enzyme

Various metabolic processes taking place inside cells are also carried out in mitochondria. Consequently, it also has a massive number of enzymes.

Citrate synthase, Aconitase, Isocitrate dehydrogenase, Alpha-ketoglutarate dehydrogenase complex, Succinate thiokinase, Succinate dehydrogenase, Fumarase and Malate dehydrogenase are the enzyme involved in the tricarboxylic acid cycle during which pyruvate and other carboxylic acid obtained are oxidized into simple carbohydrate molecule.
Pyruvate carboxylase and Malate dehydrogenase are involved in gluconeogenesis.
Carbamoyl phosphate synthetase and Ornithine transcarbamoylase are involved in the urea cycle.

Nuclear Enzyme

The nucleus contains both genetic material and enzymes which are also involved in cellular metabolisms such as DNA replication, transcription, and mitosis. The enzymes involved in the process are DNA Polymerase, RNA Polymerase, Nucleoside dehydrogenase, Nucleoside phosphorylase, Helicase, Ligase, Topoisomerase, Telomerase, DNA primase, Endonucleases, Exonucleases and DNA repair enzymes.

Extracellular Enzyme

The extracellular enzymes are the enzymes which are present in the extracellular fluid. The reaction takes place outside the cell present in tissue spaces, in body fluids like saliva and blood, and cavities of organs like the stomach and intestine.

Salivary Enzyme

Salivary gland produces saliva which contains enzymes that help in the digestion of food. The enzymes involved in the process of digestion are esterase, alpha amylase, lipase, carbonic anhydrase, and lysozymes.

Pepsin helps in partial digestion of protein particles. It is initially inactive as pepsinogen and gets activated as pepsin by hydrochloric acid present in the stomach.
Trypsin helps in the digestion of protein particles. It is produced as trypsinogen by the pancreas and is activated by enterokinase enzymes produced by the duodenum.
Chymotrypsin is produced by chymotrypsinogen. It is activated by trypsin enzymes and helps in protein digestion.
Elastases and Collagenase are proteolytic enzymes which break elastin and collagen fibres present in food.
Pancreatic amylase is an enzyme produced by the pancreas that is involved in carbohydrate digestion.

Intestinal Enzyme

Intestinal enzymes are the enzymes which help in the final digestion of food, and they are:

Peptidases are enzyme which breaks peptide bonds of protein into amino acid and
Sucrase are enzyme which breaks sucrose into glucose and fructose
Maltase are enzymes which digest maltose into two glucose molecules.
Lactase are enzymes which break lactose into glucose and galactose.

Difference Between Intracellular and Extracellular Enzyme

Intracellular	Extracellular
Present inside the cell	Present in extracellular fluid
Also known as endoenzymes	Also known as exoenzymes
Digest large polymer into small chains of monomer	Digest large polymer into small chain of monomer one at a time
Simple mechanism of digestion	Complex mechanism of digestion

Interesting Facts

Several places in your digestive system produce enzymes.
Different types of enzymes are produced for digesting different foods.
Production of enzymes decreases as our body gets older.

Key Features

Both intracellular and extracellular enzymes are involved in body metabolism
The difference is that intracellular enzymes are produced within the cell and extracellular enzymes are produced outside the cell.
The enzymes present in cytoplasm and mitochondria are involved in both gluconeogenesis and in the urea cycle.

Want to read offline? download full PDF here

Download full PDF

Is this page helpful?

FAQs on Intracellular and Extracellular Enzymes in Cells

1. What are intracellular and extracellular enzymes?

Intracellular and extracellular enzymes are enzymes that function inside the cell or outside the cell, respectively. Intracellular enzymes catalyze reactions within the cytoplasm or organelles of a cell, while extracellular enzymes are secreted outside the cell to break down substances in the external environment.

Intracellular enzymes: Act in processes like glycolysis and cellular respiration.
Extracellular enzymes: Help in digestion or nutrient breakdown, such as amylase in saliva.

This classification is based on the enzyme’s location of action in biological systems.

2. What is the main difference between intracellular and extracellular enzymes?

The main difference between intracellular and extracellular enzymes is the location where they perform their function. Intracellular enzymes work inside the cell, whereas extracellular enzymes are secreted outside the cell to act on external substrates.

Location: Inside cell vs. outside cell
Function: Internal metabolism vs. external digestion
Example: DNA polymerase (intracellular) vs. pepsin (extracellular)

This difference is important in understanding cellular metabolism and digestion.

3. What are examples of intracellular enzymes?

Examples of intracellular enzymes include enzymes that function within the cell during metabolic reactions. Common intracellular enzymes include:

Catalase – breaks down hydrogen peroxide in peroxisomes
DNA polymerase – synthesizes DNA during replication
ATP synthase – produces ATP in mitochondria
Hexokinase – catalyzes the first step of glycolysis

These enzymes are essential for cell survival, growth, and energy production.

4. What are examples of extracellular enzymes?

Examples of extracellular enzymes include enzymes secreted outside the cell to break down large molecules. Common extracellular enzymes include:

Amylase – breaks down starch into sugars
Proteases such as pepsin – digest proteins
Lipase – breaks down fats into fatty acids and glycerol
Cellulase – breaks down cellulose (in fungi and bacteria)

These enzymes play a major role in digestion and nutrient absorption.

5. How do extracellular enzymes work?

Extracellular enzymes work by being secreted out of the cell to break down complex molecules into simpler substances that can be absorbed. The process involves:

1. Synthesis of the enzyme inside the cell.
2. Secretion through the cell membrane via exocytosis.
3. Binding to a specific substrate outside the cell.
4. Catalyzing the breakdown into smaller, absorbable molecules.

This mechanism is common in digestion and in microorganisms that decompose organic matter.

6. Why are intracellular enzymes important?

Intracellular enzymes are important because they regulate and speed up essential metabolic reactions within the cell. They are crucial for:

Cellular respiration and ATP production
DNA replication and repair
Protein synthesis
Detoxification of harmful substances

Without intracellular enzymes, vital biochemical reactions would occur too slowly to sustain life.

7. Why are extracellular enzymes important in digestion?

Extracellular enzymes are important in digestion because they break down large food molecules into smaller units that can be absorbed by cells. In humans:

Amylase converts starch into maltose.
Proteases break proteins into amino acids.
Lipase breaks fats into fatty acids and glycerol.

These digestive enzymes function outside individual cells but within body cavities such as the mouth, stomach, and small intestine.

8. Where are intracellular enzymes found in the cell?

Intracellular enzymes are found in the cytoplasm and various organelles of the cell. They are located in:

Cytoplasm – e.g., glycolytic enzymes
Mitochondria – e.g., enzymes of the Krebs cycle
Nucleus – e.g., RNA polymerase
Lysosomes – digestive enzymes

Their location depends on the specific metabolic pathway or cellular process they control.

9. Can the same organism produce both intracellular and extracellular enzymes?

Yes, the same organism can produce both intracellular and extracellular enzymes depending on its metabolic needs. For example:

Bacteria produce intracellular enzymes for energy metabolism.
The same bacteria may secrete extracellular enzymes like proteases to digest external nutrients.
Humans use intracellular enzymes for cellular processes and extracellular enzymes for digestion.

This dual production allows organisms to efficiently obtain and utilize nutrients.

10. How are extracellular enzymes secreted from the cell?

Extracellular enzymes are secreted from the cell through the process of exocytosis. The steps include:

1. Synthesis of the enzyme in the rough endoplasmic reticulum.
2. Modification and packaging in the Golgi apparatus.
3. Transport in secretory vesicles to the cell membrane.
4. Fusion of vesicles with the membrane to release the enzyme outside the cell.

This secretory pathway is common in gland cells and many microorganisms.