Biochemical Compounds: Definition & Classes

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Biochemical compounds sound very impressive, but what are they? Learn about biochemical compounds, the classes of biochemical compounds, and how they are essential to life. Then see what you've learned by taking a quiz.

What Is a Biochemical Compound?

Your body is full of biochemical compounds. Without them, plants and animals wouldn't exist - they're the compounds that make up living things.

All life on Earth is carbon-based, which means that the large molecules that make up much of our body all contain carbon. In some sci-fi stories, humans find silicon-based life on other planets. That's because silicon has a lot of similarities with carbon. But as far as we know, all life is carbon-based. So for the moment, that's how we define biochemical compounds.

A compound is a substance made of molecules that contain two or more elements bonded together. A biochemical compound is any compound that contains carbon and is found in living things. They're involved in every process of life: growth, digestion, respiration, you name it. In the real world, all biochemical molecules contain hydrogen and oxygen. They might also contain nitrogen, sulfur and phosphorus.

The biggest biochemical molecule ever discovered is titin. It's found in muscles and contains 169,723 carbon atoms, 270,464 hydrogen atoms, 45,688 nitrogen atoms, 522,243 oxygen atoms and 912 sulfur atoms. We call it titin because its real name is too hard to say. It would take a person around half an hour!

Classes of Biochemical Compounds

Humans love to classify things. We like to give everything a name, and put things into boxes. That's why we have mammals, reptiles, birds, and amphibians. It's also why we have planets, dwarf plants, asteroids and comets. So it's probably not surprising to learn that we did the same thing with biochemical compounds.

There are four classes of biochemical compounds: carbohydrates, proteins, lipids (fats), and nucleic acids. Perhaps you recognize those names from nutrition - these are four things we get from our food. Considering this is what much of our body is made of (not counting water), it makes sense that we need to feed our body the same kinds of molecules. But what exactly are carbohydrates, proteins, lipids, and nucleic acids?

Carbohydrates are molecules made up of carbon, oxygen, and hydrogen. They usually have twice as much hydrogen as oxygen. Examples of carbohydrates include sugars, starches and cellulose.

Example of a carbohydrate (glucose)
Example of a carbohydrate (glucose)

Proteins are molecules made up of long chains of amino acids. They're more complex than carbohydrates and contain carbon, oxygen, hydrogen, nitrogen, and sulfur. Examples of proteins include hormones and enzymes.

Example of a protein
Example of a protein

Lipids are small, hydrophobic molecules built from fatty acids. They're not soluble in water, but can be dissolved in organic solvents. Like carbohydrates, they usually contain only carbon, oxygen, and hydrogen. Examples of lipids include the fat stores around your body, but also oils and waxes.

Butter contains mostly fats, which are a type of lipid
Butter contains mostly fats

Nucleic acids are biological polymers made from nucleotides. They're the most complex of the classes of biochemical compounds and are built from many parts, including sugars, which are themselves carbohydrates. They contain the same elements as proteins, except tend to have phosphorus instead of sulfur. But it's the way those elements are bonded together that makes them nucleic acids. Examples of nucleic acids include DNA and RNA.

Example of a nucleic acid: a DNA molecule
Example of a nucleic acid: a DNA molecule

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