I always think of enzymes as being like my father. Just as he simplifies my chaotic life, enzymes break down complex molecules, making it easier for our bodies to function. Just like fathers are the superheroes of our lives, enzymes are the superheroes of our bodies.
What Are Enzymes?
Before exploring digestive enzymes, let’s first uncover the basics of what enzymes are and how they work.
Enzymes are tiny protein machines in our bodies, made from chains of different amino acid sequences folded into unique shapes. In every enzyme, there is a special 3D pocket called the active site, where a substance known as a substrate fits in and gets turned into a new product.
One of the main jobs of enzymes is to lower the activation energy (Ea) needed for a reaction, making the process of product formation faster than without the enzyme.
Digestive Enzymes: Breaking Down Food
Digestive enzymes work in a similar way. Digestion is a key process in our body, and digestive enzymes are like helpers in breaking down food. The food we eat—carbohydrates, fats, and proteins—contains complex molecules that our cells can’t use right away.
Digestive enzymes break these complex molecules into simpler ones and make it easier for our cells to turn them into the energy that our body needs to function.
One thing I must say is that carbohydrates, fats (lipids), and proteins need to be digested because they have complex structures. However, vitamins, water, and minerals are simple molecules that do not need digestion; our body can absorb and use them directly.
Carbohydrate Digestion
Mouth (Carbohydrate)
Imagine your favorite dish right in front of you. Even just thinking about it can make your mouth start to water. That’s because of three special glands in your mouth:
- Parotid gland
- Submandibular gland
- Sublingual gland
These glands release saliva (the watery substance in your mouth) packed with helpful enzymes, including salivary amylase (or ptyalin), a bit of maltase, and lysozyme. This saliva helps kickstart digestion before you even take a bite!
When you eat foods like rice, pasta, wheat, potatoes, or bread, which are rich in starch, the enzyme ptyalin (also known as salivary amylase) starts breaking down the starch into maltose. Once maltose is formed, another enzyme, maltase, takes over and converts it into glucose. Because of these glucose molecules, you feel a bit of sweetness in your mouth when you eat carbohydrate-containing food.
You might wonder why we need further digestion of carbohydrates if we already start breaking them into glucose in our mouth.
The reason is that the small amount of maltase enzyme in the mouth takes a long time to convert maltose into glucose. But until then, we usually do not keep food in our mouth, so most of the maltose remains undigested at this stage. That’s why the rest of the digestion happens in your stomach and intestines to fully break down carbohydrates into glucose for energy.
But what’s the function of lysozyme?
The lysozyme enzyme helps destroy bacteria that are present in the food we are eating, ensuring that the food entering your stomach is relatively free of these harmful microorganisms.
You might have noticed that babies often drool excessively, with saliva spilling out of their mouths. This is because their saliva production is high, which serves as a protective mechanism. Since babies explore the world by putting everything in their mouths, the lysozyme enzyme in saliva helps to protect them from harmful bacteria, ensuring that their mouths and bodies remain healthier despite their exploratory habits.
That’s cute, right?
Stomach (Carbohydrate)
In the stomach, there is no enzyme that helps in the digestion of carbohydrates. The bolus (the food that came from the mouth) is mixed with HCl and becomes acidic.
Small Intestine (Carbohydrate)
The acidic food molecules now come into the final stage of digestion, the duodenum in the small intestine.
Here, carbohydrates are completely digested and converted into glucose, fructose, galactose, and simple dextrin, which can be used by our cells.
But here comes a problem.
Acidic food molecules cannot be digested by the enzymes present in the small intestine. Bile comes with its component to solve this problem. Sodium bicarbonate (NaHCO₃), a component of bile, neutralizes the acidic environment because other necessary enzymes do not work effectively in that acidic condition. Sodium bicarbonate neutralizes the acidic conditions in your duodenum and creates a perfect alkaline environment.
And problem solved!
All types of food are fully digested in the small intestine.
For carbohydrates, enzymes like amylase (not the salivary amylase), isomaltase, maltase, sucrase, and lactase break down complex carbohydrates into simple compounds.
These are hydrolytic enzymes, and for their proper function, water is must.
Protein Digestion
Mouth (Protein)
No enzyme is present for breaking down protein, so no digestion occurs here.
Stomach (Protein)
Let me introduce to you a new juice: gastric juice.
The wall of the stomach is muscular. As the chewed food arrives from the mouth, the stomach muscles churn and mix it into a dense, soup-like mixture called chyme.
Numerous gastric glands are present in the wall of the stomach, made up of four types of cells. Each type of cell has a different secretion. The combined secretion of the gastric glands is called ‘gastric juice.’
In the stomach, protein digestion is powered by two key enzymes: pepsinogen and prorenin.
However, they are initially inactive. This is where gastric juice comes into play.
The stomach’s parietal cells secrete hydrochloric acid (HCl), a critical component in the digestive process. HCl serves a dual purpose: it creates an acidic environment and activates pepsinogen and prorenin into their active forms, Pepsin and Renin.
A protein named gelatin is also present in animal meat. For the digestion of this protein, gelatinase is used. Proteoses and peptones are formed, but amino acids are not yet produced, which can be synthesized by our cells. Now, for these amino acids, let’s move on to the small intestine.
Small Intestine (Protein)
In the small intestine, specifically the duodenum, the enzyme enterokinase plays an amazing role in digestion. It activates the trypsinogen enzyme, turning it into its active form, trypsin. This activated trypsin, along with another enzyme named chymotrypsin, breaks down proteoses and peptones into smaller chains known as polypeptides.
But the process doesn’t stop there.
A team of enzymes—carboxypeptidase, aminopeptidase, dipeptidase, tripeptidase, collagenase and Elastase—work together to break down these polypeptides even further. Their combined effort results in the production of amino acids, the building blocks for the growth and repair of the body.
Lipid Digestion
Mouth (Lipid)
No enzymes are present for lipid digestion in the mouth, so no digestion occurs.
Stomach (Lipid)
No significant digestion happens in the stomach either, though it is thought that gastric lipase from the stomach wall digests lipids a bit, forming fatty acids and glycerol.
Small Intestine (Lipid)
This half-digested lipid moves to the small intestine, where it is finally digested.
Before digestion, there is a step where bile salts (sodium glycocholate, sodium taurocholate) from bile convert lipid foods into very tiny molecules, making digestion more convenient. This step is known as emulsification.
Enzymes from pancreatic juice, like lipase, phospholipase and cholesterol esterase convert lipid molecules and phospholipids into fatty acids and glycerol.
Intestinal juice contains enzymes like lipase and lecithinase that further break down lipid molecules.
Other Enzymes
Some other enzymes like nucleotidase, nucleosidase, and nuclease also break down nucleic acids into phosphate groups, pentose sugar, and nitrogen bases.
The Ending
Just as a well-coordinated team of experts helps a project succeed, enzymes collaborate seamlessly within us to keep our bodies running smoothly.
From the first bite to the final nutrient, enzymes make it all possible. These small but powerful helpers transform our food into energy, breaking down complex molecules so our bodies can thrive.
So, as you enjoy your next meal, remember the enzymes working quietly in the background—keeping us nourished, energized, and ready for whatever comes next.
