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Intracellular and Extracellular Enzyme

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Enzymes – An Introduction

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



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.

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FAQs on Intracellular and Extracellular Enzyme

1. Why are plant derived enzymes effective?

Plant-derived enzymes are effective over a broader pH range in the body. For this reason, a plant-based digestive enzyme supplement is often recommended to help break down a wide variety of foods—including proteins, fats, dairy, carbs, and sugars.

2. What are the digestive enzymes humans lack?

There are several digestive enzymes the human body lacks. These include cellulase and phytase, the enzymes are needed to break down cellulose (plant fiber) and the phytates/phytic acid found in beans and legumes. Because of this deficiency, many people have trouble breaking down starchy beans, legumes, and nuts to absorb their beneficial nutrients.

3. How does temperature affect the activity of enzymes?

Enzymes accelerate processes when temperatures are greater. Increasing the temperature by merely 2 degrees can hasten reactions by 20%. When the temperature is too high, the enzyme activity is drastically reduced.

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