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Chemical Reaction Definition in Biology

Instructor: Amanda Robb
In this lesson, we'll go over what a chemical reaction is and discuss some key examples in biology. By the time we're through, you will know why chemical reactions are important for living things.

What is a Chemical Reaction?

Stop for a second and feel your heart beat. The lump dump sound in your chest is responsible for pumping oxygen-rich blood all over your body. As the blood reaches your cells, it picks up carbon dioxide, which is toxic to your body. The carbon dioxide is converted at lightning speed to a chemical - carbonic acid - that can be readily transported through the blood. The blood goes to the lungs, you breathe out the carbon dioxide, and keep living.

Carbon dioxide is converted to carbonic acid in the blood to keep you alive
blood vessel

If this didn't happen, carbon dioxide would build up in your tissues. You would start to hyperventilate, your brain would stop working and death would eventually ensue. The reason this doesn't happen is because of a chemical reaction, or a process in which one or more substances are changed into another substance. Carbon dioxide is changed to carbonic acid, which dissolves easily in blood to be transported back to the lungs. Today, we'll learn more about types of chemical reactions in biology and why they are important.

Chemical Reactions in Biology

Chemical reactions are crucial for life on earth. However, most chemical reactions in the body would occur very slowly without a molecule called an enzyme. Enzymes are catalysts that speed up chemical reactions. Reactions outside living things usually do not use enzymes, thus enzymes are specific to chemical reactions in biology.

Enzymes not only make reactions go faster, but also help living things control when and where reactions happen. Our cells send signals to enzymes to regulate when they should be doing their job, which allows the body to control specific functions, such as transporting carbon dioxide.

Chemical reactions start with molecules called reactants and convert them into products, or the end result of the reaction. Think of chemical reactions like people making goods in a factory. The raw materials they start with are the reactants, the people creating the goods are like the enzymes and the end materials that are shipped out are literally the products created.

Chemical reactions with enzymes
chemical reactions with enzymes

Although every process of all living things needs chemical reactions, today we'll look at a few key examples: chemical reactions that make energy, chemical reactions that plants use to make food, and chemical reactions that can cause illness.

Chemical Reactions that Make Energy

Chemical reactions are crucial for our cells to make energy, or ATP. All living things need energy to survive and ATP is actually a reactant that drives many other chemical reactions inside cells. Cells use a process called cellular respiration to make energy. The overall reaction uses glucose and oxygen as reactants and makes carbon dioxide and ATP as products.

Equation for cellular respiration
cellular respiration equation

Within cellular respiration, there are many steps and each is catalyzed by a specific enzyme. For example, the first step to starting cellular respiration involves bringing glucose into the cell. When a cell brings in glucose, it needs to add a molecule called a phosphate group to the glucose to keep it inside. The phosphate group prevents the glucose from escaping the cell. In this chemical reaction an enzyme called hexokinase takes a phosphate group from ATP and puts it on the glucose. Without this chemical reaction, sugar could never get into our cells and we would not be able to make any energy. In short, our muscles would stop working and we would suffocate, all because of one chemical reaction!

Chemical reaction adding a phosphate to glucose
glucose 6 phosphate

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