Substrate

Substrate Definition

An enzyme acts on a substrate, which is a molecule. The substrate is loaded into the active site of the enzyme, or the area where weak bonds can form between molecules. By exerting forces on the substrate, the enzyme forms an enzyme substrate complex, and the enzyme reacts with the substrate, resulting in the intended reaction product. 

The bonds that form between the substrate and enzyme cause the enzyme’s conformational change. As a result of the shape change, pressure is applied to the substrate, tearing or forcing molecules together.

At some point in our lives, every molecule in our bodies is a substrate molecule. Each reaction requires an enzyme to help it along because most reactions require a large amount of energy and time. Enzymes accomplish this by reducing the energy required for a reaction to take place between substrate molecules, or within one molecule. Following the reaction, the substrate becomes chemically different, and is called the product. 

Nevertheless, the majority of chemicals produced by our bodies are made up of many smaller steps, known as intermediates, which each have their own enzyme. Until a final product is reached, the products of one reaction become the substrate for the next. All the materials in our body are formed this way.

The gut digests nutrients collected by an organism. Enzymes act on various forms of food as substrates and break them apart. As soon as these products are broken down, they are carried to various cells throughout the body. Now called substrates again, new enzymes work on these substances to combine them into bigger molecules and incorporate them into the body. Whether or not a substance is considered a substrate is dependent on which reaction it is headed to, and which reaction it came from. 

After a substrate becomes a product, it can instantly become a substrate again if a different enzyme can act on it. Because enzymes are specific and decrease reaction time, we can produce many chemicals that would be completely impossible without intermediate steps, and enzymes doing most of the work.

Examples of Substrate

Lactose

Lactose is a sugar found in milk. For their offspring, mammals usually produce milk. A combination of fats, proteins, and growth hormones makes a young mammal gain a lot of weight quickly. In a non-predatory manner, humans are the only animals capable of drinking another species’ milk. 

Only humans purposefully drink cow milk, whereas some big predators will consume the milk of the mammal they just killed. It is not surprising that many people have lactose intolerance, which is the inability to process the sugar lactose.

In order to deal with lactose in breast milk, humans produce lactase, the enzyme needed to act on lactose as a substrate. When weaned from breastmilk, lactose is no longer present for the enzyme to work on. 

Lactose not only acts on your DNA, but it is also a substrate for lactase. Lactase is thought to be produced more by DNA in the presence of lactose. After weaning, the body produces little to no lactase, causing lactose intolerance. 

The majority of people continue to drink cow’s milk almost immediately after weaning from breast milk. By doing so, you are continuously able to digest lactose, which might not be a good thing. As an adult mammal, studies have shown that the growth hormones, cholesterol, and animal proteins in cow’s milk may be harmful to your health. The fact that adults shouldn’t drink baby formula does make sense, however.

ACE Inhibitors as Substrate Blockers

If you know of anyone currently taking ACE inhibitors, you probably know that the pills help keep them alive, but you have no idea how. ACE stands for angiotensin converting enzyme. This enzyme produces a molecule known as angiotensin II, which causes muscles around blood vessels to contract. 

These small muscles pressure the blood. Normally, they help keep the blood flowing with healthy pressure. If too much angiotensin II is created by the body, or if the blood vessels are clogged, more pressure can cause the vessels to burst or become completely sealed off. Both are life-threatening conditions.

Luckily, ACE inhibitors were created to mimic substrates. The ACE inhibitors are about the same size and shape as angiotensin I, the substrate for the angiotensin-converting enzyme. Instead of binding to the substrate, the enzyme binds to the inhibitor instead. Unlike the substrate, the inhibitor cannot undergo a chemical reaction and sticks to the enzyme. 

By regulating the amount of ACE inhibitor given to a person, the effectiveness of all their angiotensin-converting enzymes can be affected. A lower level of angiotensin II will be seen in the blood and tissues. Without this chemical, the muscles around blood vessels relax, and blood pressure is lowered. Lower blood pressure prevents many of the dangerous conditions that can arise from high blood pressure.

Related Biology Terms

• Enzyme Substrate Complex – A large pseudomolecule formed when a substrate enters the active site of an enzyme.
• Conformational Change – A structural shift in an enzyme due to the formation of the enzyme-substrate complex.
• Intermediate – A molecule that serves no function, but exists as a part of a pathway to another molecule.
• Active Site – The place on an enzyme that the substrate can weakly bind to, causing a conformational change in the enzyme.

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