Carbon is the most important element to life. Without this element, life as we know it would not exist. As you will see, carbon is the central element in compounds necessary for life.
A compound found mainly in living things is known as an organic compound. Organic compounds make up the cells and other structures of organisms and carry out life processes. Carbon is the main element in organic compounds, so carbon is essential to life on Earth. Without carbon, life as we know it could not exist.
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A compound is a substance that consists of two or more elements. A compound has a unique composition that is always the same. The smallest particle of a compound is called a molecule. Consider water as an example. A molecule of water always contains one atom of oxygen and two atoms of hydrogen. The composition of water is expressed by the chemical formula H2O. A model of a water molecule is shown in the Figure below. Water is not an organic compound.
What causes the atoms of a water molecule to “stick” together? The answer is chemical bonds. A chemical bond is a force that holds molecules together. Chemical bonds form when substances react with one another. A chemical reaction is a process that changes some chemical substances into others. A chemical reaction is needed to form a compound. Another chemical reaction is needed to separate the substances in a compound.
Why is carbon so basic to life? The reason is carbon’s ability to form stable bonds with many elements, including itself. This property allows carbon to form a huge variety of very large and complex molecules. In fact, there are nearly 10 million carbon-based compounds in living things! However, the millions of organic compounds can be grouped into just four major types: carbohydrates, lipids, proteins, and nucleic acids. You can compare the four types in the Table below. Common structural examples of the four major types of organic compounds are included in the table. Notice the diversity of structures among the organic compounds listed.
| Type of Compound | Examples | Structure | Elements | Functions | Monomer |
|---|---|---|---|---|---|
| Carbohydrates | sugars, starches |
|
carbon, hydrogen, oxygen | provides energy to cells, stores energy, forms body structures | monosaccharide |
| Lipids | fats, oils |
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carbon, hydrogen, oxygen | stores energy, forms cell membranes, carries messages | |
| Proteins | enzymes, antibodies |
|
carbon, hydrogen, oxygen, nitrogen, sulfur | helps cells keep their shape, makes up muscles, speeds up chemical reactions, carries messages and materials | amino acid |
| Nucleic Acids | DNA, RNA |
|
carbon, hydrogen, oxygen, nitrogen, phosphorus | contains instructions for proteins, passes instructions from parents to offspring, helps make proteins | nucleotide |
Carbohydrates, proteins, and nucleic acids are large molecules known as polymers (also referred to as macromolecules) built from smaller molecules (monomers) through dehydration reactions. In a dehydration reaction, water is removed as two monomers are joined together. Hydrolysis is a reaction where polymers are broken down; a water molecule is split, separating a monomer away from the polymer chain.
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