Enzymes help accelerate chemical reactions in the human body. They bind to molecules and modify them in certain ways. They are necessary for breathing, digesting food, running muscles and nerves, but also in thousands of other roles.
Enzymes are made of proteins folded into complex shapes. They may also be joined to other non-protein substances and are present throughout the body. The chemical reactions that keep us alive – our metabolism – are based on the work that enzymes perform.
Enzymes accelerate (catalyze) chemical reactions. In some cases, enzymes can make a chemical reaction millions of times faster than they would have been without it.
A substrate is connected to the active position of an enzyme and converted into products. Once the products leave the active area, the enzyme is ready to cling to a new substrate and repeat the process.
What do enzymes do?
In the digestive system – Enzymes help the body break down larger complex molecules into smaller molecules, such as glucose, so that the body can use them as fuel.
DNA copying – Every cell in your body contains DNA. Every time a cell is divided, the DNA must be copied. Enzymes help in this process by unfolding the double hel of DNA and copying the information.
In the liver -Liver enzymes break down toxins in the body so that it eliminates them more easily. To do this, a number of enzymes are used.
How do enzymes work?
The "lock and key" model was first proposed in 1894. In this model, the enzyme's hotspot has a specific shape and only the substrate will fit into it, such as the key in the lock. This model has now been updated and is called an induced customization model.
In this model, the active center of the enzyme changes shape as it interacts with the substrate. Once the substrate is fully locked and in the exact position, catalysis can begin.
The perfect conditions
Enzymes can only work under certain conditions. Most enzymes in the human body work best at about 37° C – body temperature. At lower temperatures, they will still work but much slower. Similarly, enzymes can only work within a certain pH range (acid/alkaline). Their preference depends on where they are in the body.
For example, enzymes in the intestines work best at 7.5 pH, while enzymes in the stomach work better at pH 2 because the stomach is much more acidic.
If the temperature is too high or if the environment is too acidic or alkaline, the enzyme changes shape. This alters the shape of the active position so that the substrates cannot bind to it – the enzyme has been denatured.
Some enzymes cannot work unless they have a specific non-protein molecule attached to them. These are called co-factors.
For example, carbonic reaction, an enzyme that helps maintain the body's pH, cannot work unless it is linked to zinc ions.
To ensure that the body's systems work properly, sometimes enzymes need to be slowed down. For example, if an enzyme produces too much of a product, there must be a way to reduce or stop production. Enzyme activity can be inhibited in many ways:
- Competitive inhibitors – a molecule blocks the active position so that the substrate must compete with the inhibitor to connect to the enzyme.
- Non-competitive inhibitors – a molecule binds to an enzyme somewhere other than the active space and reduces how effectively it works.
- Adjustment with feedback – the product of the enzyme's reaction to the substrate can act as an inhibitor. If they exceed a concentration, the products leave the active center less accessible and the reaction slows down.
- Irreversible inhibitors – an irreversible inhibitor binds to an enzyme and permanently disables it.
Examples of specific enzymes
There are thousands of enzymes in the human body, here are just a few examples:
- Lipases – a group of enzymes that help digest fats in the gut.
- Amylase – helps break down starch into smaller sugars. Amylase is found in saliva.
- Maltais– also found in saliva. Breaks down maltose into glucose. Maltose is found in foods such as potatoes, pasta, and beer.
- Trypsin – located in the small intestine, breaks down proteins into amino acids.
- Lactase, which is also found in the small intestine, breaks down lactose, sugar in milk, glucose, and galactose.
- Acetylcholinesterase – catabolizes the neurotransmitter acetylcholine in nerves and muscles.