What makes up a healthy diet?
A healthy diet includes protein, fats, and carbohydrates. Why? Because these compounds are three of the main building blocks that make up your body. You obtain these building blocks from the food that you eat, and you use these building blocks to make the organic compounds necessary for life.
Drawing on Student Experiences
What do you know about organic compounds?
How is the word organic in science different than organic in the grocery store?
Organic compounds are chemical substances that make up organisms and carry out life processes. All organic compounds contain the elements carbon and hydrogen. Because carbon is the major element in organic compounds, it is essential to all known life on Earth. Without carbon, life as we know it could not exist.
Why is carbon so important to organisms? The answer lies with carbon’s unique properties. Carbon has an exceptional ability to bind with a wide variety of other elements. Carbon atoms can form multiple stable bonds with other small atoms, including hydrogen, oxygen, and nitrogen, phosphorus and sulfur. Carbon atoms can also form stable bonds with other carbon atoms. This allows carbon atoms to form a tremendous variety of very large and complex molecules.
Nearly 10 million carbon-containing organic compounds are known. Types of carbon compounds in organisms include carbohydrates, lipids, proteins, and nucleic acids. The Chart below contains the four main types of organic molecules, the elements they contain and examples of each type.
Type of Compound
Elements It Contains
Carbon, hydrogen, oxygen
Glucose, Starch, Glycogen, Breads, Cereals
Carbon, hydrogen, oxygen
Cholesterol, Triglycerides (fats) Phospholipids, Wax, Oil
Carbon, hydrogen, oxygen, nitrogen, sulfur
Enzymes, Antibodies, Meat, Beans
Carbon, hydrogen, oxygen, nitrogen, phosphorus
Living things are made up of very large molecules. These large molecules are called macromolecules because “macro” means large; they are made by smaller molecules bonding together. Our body gets these smaller molecules, the "building blocks" of organic molecules from the food we eat.
Carbohydrates are organic compounds that contain only carbon, hydrogen, and oxygen. They are the most common of the four major types of organic compounds. There are thousands of different carbohydrates.
Carbohydrates are sugars, or long chains of sugars. An important role of carbohydrates is to store energy. Glucose (Figure below) is an important simple sugar molecule with the chemical formula C6H12O6. Simple sugars are known as monosaccharides.
Carbohydrates also include long chains of connected sugar molecules. These long chains often consist of hundreds or thousands of monosaccharides bonded together to form polysaccharides.
Plants store sugar in polysaccharides called starch. Animals store sugar in polysaccharides called glycogen. You get the carbohydrates you need for energy from eating carbohydrate-rich foods, including fruits and vegetables, as well as grains, such as bread, rice, or corn.
An example of a disaccharide is sucrose (table sugar), which consists of the monosaccharides glucose and fructose. Monosaccharides and disaccharides are also called simple sugars. They provide the major source of energy to living cells.
A molecule of glucose, a type of carbohydrate.
Proteins are organic compounds that contain carbon, hydrogen, oxygen, nitrogen, and, in some cases, sulfur. Common substances around your house are made of proteins such as meat, eggs and beans. Your hair and skin are made of proteins. Proteins are made of smaller units called amino acids. There are 20 different common amino acids needed to make proteins.
Small proteins can contain just a few hundred amino acids. Yeast proteins average 466 amino acids. The largest known proteins are the titins, found in muscle, which are composed from almost 27,000 amino acids.
Amino acids connect together like beads on a necklace. MET, ASN, TRP, and GLN refer to four different amino acids.
Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein (Figure below).
Muscle fibers are made mostly of protein.
It’s important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat!
Lipids are organic compounds that contain mainly carbon, hydrogen, and oxygen. They include substances such as fats and oils. Lipid molecules consist of fatty acids.
Have you ever tried to put oil in water? They don’t mix. Oil is a type of lipid. Lipids are molecules such as fats, oils, and waxes. The most common lipids in your diet are probably fats and oils. Fats are solid at room temperature, whereas oils are fluid. Animals use fats for long-term energy storage and to keep warm. Plants use oils for long-term energy storage. When preparing food, we often use animal fats, such as butter, or plant oils, such as olive oil or canola oil. There are many more type of lipids that are important to life. One of the most important are the phospholipids that make up the protective outer membrane of all cells (Figure below).
Phospholipids in a membrane, shown as two layers (a bilayer) of phospholipids facing each other.
Nucleic acids are organic compounds that contain carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are made of smaller units called nucleotides. Nucleic acids are named for the nucleus of the cell, where some of them are found. Nucleic acids are found not only in all living cells but also in viruses. Types of nucleic acids include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
A model representing DNA, a nucleic acid.
You just read about how the 4 main types of organic compound are made of multiple smaller molecules. What do you think happens to each of the organic compounds during digestion? Be specific to each type of organic compound!
- amino acid: Small molecule used to build proteins.
- carbohydrate: Organic compound such as sugar and starch that provides an energy source for animals.
- enzyme: Protein that speeds up chemical reactions.
- glucose: Simple sugar molecule with the chemical formula C6H12O6.
- lipid: Organic compound that is insoluble in water and includes fats, oils, and waxes.
- nucleic acid: Organic compound that can carry genetic information.
- organic compound: Compound built around the element carbon.
- protein: Organic compound composed of amino acids and includes enzymes, antibodies, and muscle fibers.
- Living organisms are comprised of organic compounds, molecules built around the element carbon.
- Organic compounds contain carbon and hydrogen and may contain other elements such as oxygen, nitrogen, phosphorus and sulfur.
- Living things are made of just four classes of organic compounds: proteins, carbohydrates, lipids, and nucleic acids.
- Carbon’s exceptional ability to form bonds with other elements and with itself allows it to form a huge number of large, complex molecules called organic molecules. These molecules make up organisms and carry out life processes.
- What elements do all organic compounds contain?
- What are some other elements organic compounds may contain?
- What are the four organic compounds that make up living things?
- What are examples of lipids?
- What are examples of proteins?
- What are examples of carbohydrates?