Digestive Enzymes

The Function of Digestive Enzymes

Digestive enzymes help in the digestion of food. The food that we eat consists of carbohydrates, lipids, proteins, and nucleic acids. We eat these biomolecules because our body needs them for growth and repair. But our body cannot take them up in their large form since they are too big to be absorbed in the intestine and enter the blood. Our digestive enzymes correct this by turning these large essential biomolecules into smaller building blocks by breaking the chemical bonds between them.

Digestive enzymes are produced at various parts of the digestive system and are eventually added to the semi-fluid food passing through the digestive tract.

Types of Digestive Enzymes

Digestive enzymes can be classified into three main categories based on the types of molecules they act on. These three classes are carbohydrases, proteases, and lipases.

Carbohydrase

Carbohydrases are a family of digestive enzymes that hydrolyse complex carbohydrates into simple sugars.

$Carbohydrates\stackrel{Carbohydrase}{\to }Simple\mathrm{s}ugars$

We eat various types of carbohydrates in our food, and each requires its own carbohydrase enzyme. These enzymes are produced in different sections of the digestive system, such as the salivary glands, pancreas, and small intestine.

Proteases

Proteases, or proteolytic enzymes, refer to a group of enzymes whose catalytic function is to break down protein molecules.

Proteases act by hydrolysing peptide bonds, although the ability of proteases to break different peptide bonds varies. Proteases are produced in the stomach and pancreas, after which they are released into the digestive tract.

$Proteins\stackrel{Protease}{\to }Peptides\mathit{}and\mathit{/}or\mathit{}amino\mathit{}acids$

Lipases

Lipases are enzymes secreted by the pancreas that break down lipids (fats) in the duodenum of the small intestine. Lipases turn lipids into their constituting subunits: fatty acids and glycerol.

$Lipids\stackrel{Lipase}{\to }Fatty\mathit{}acids\mathit{+}Glycerol$

Nucleases

Nucleases are another digestive enzyme class that breaks down nucleic acids into nucleotides. Most foods we eat, whether vegetables, fruit, or meat, consist of cells that were once alive. These cells contain nucleic acids in the form of DNA or RNA. During digestion, nucleases break down these molecules into simpler molecules.

$\mathit{N}\mathit{u}\mathit{c}\mathit{l}\mathit{e}\mathit{i}\mathit{c}\mathit{}\mathit{a}\mathit{c}\mathit{i}\mathit{d}\mathit{s}\mathit{}\mathit{(}\mathit{D}\mathit{N}\mathit{A}\mathit{}\mathit{a}\mathit{n}\mathit{d}\mathit{}\mathit{R}\mathit{N}\mathit{A}\mathit{)}\mathit{}\stackrel{\mathit{N}\mathit{u}\mathit{c}\mathit{l}\mathit{e}\mathit{a}\mathit{s}\mathit{e}}{\mathit{\to }}\mathit{}\mathit{N}\mathit{u}\mathit{c}\mathit{l}\mathit{e}\mathit{o}\mathit{t}\mathit{i}\mathit{d}\mathit{e}\mathit{s}$

Examples of Digestive Enzymes

The table below gives an overview of some digestive enzyme examples.

Table 1: Summary of digestive enzymes types, the substrate they work on, where they are produced and released into, and some examples.

In the rest of this section, we will look closely at two digestive enzymes, amylase and pepsin, which are essential enzymes needed for the chemical breakdown of carbohydrates and proteins, respectively.

Amylase

One of the most common carbohydrates we eat is starch, a long polymer made of glucose sugars. Amylase is the carbohydrase that cleaves the glycosidic bonds in starch to produce individual glucose sugar molecules. Glucose is then transported across the intestinal wall and is absorbed into the bloodstream.

Amylases are produced at multiple places along the digestive tract. They are first added in the mouth and released by the pancreas in the small intestine (duodenum).

Pepsin

Protein digestion takes place in the stomach and duodenum. Pepsin is one of the main proteases involved in protein digestion and is secreted in the stomach. In addition to pepsin, the stomach produces gastric acid or hydrochloric acid (HCl). This gastric acid lowers the pH in the stomach, making the conditions optimum for the pepsin.

The Benefits of Digestive Enzymes

Digestive enzymes are essential for splitting down food particles into substances that can be absorbed. The lack of this can lead to poor digestion and malnutrition. Let's discuss a particular disorder that can arise when certain digestive enzymes are dysfunctional.

Lactose Intolerance

Lactose intolerance is a digestive condition characterised by an inability to fully digest lactose, a significant sugar found in dairy products. Lactose intolerant individuals lack the enzyme lactase that breaks down lactose to galactose and glucose, two smaller absorbable sugars. The lactose sugar cannot be absorbed in the small intestine, so it remains in the digestive tract. As a result, individuals with lactose intolerance may experience symptoms of diarrhea, gas, and bloating after consuming dairy products.