What Are C Molecules? A Look at Carbon in Biology

“C molecule” is an informal term for carbon-containing molecules. Carbon makes up about 18% of the human body by weight and forms the structural backbone for the molecules essential for life. Its properties allow it to create a multitude of compounds, from simple methane to the complex structures of DNA. This versatility makes carbon the central element in organic chemistry, the study of compounds that are the foundation of living organisms.

Carbon’s Special Bonding Abilities

Carbon’s versatility originates from its atomic structure. A carbon atom has four valence electrons, allowing it to form four strong covalent bonds with other atoms. This tetravalent bonding capacity enables the construction of complex, three-dimensional structures. This ability makes carbon a foundational component of large molecules.

Carbon atoms can link together to form long, durable chains or branched structures. These carbon-carbon bonds are strong, providing a stable skeleton for large molecules. The chains can be thousands of atoms long or join to form ring structures, like those in sugars such as glucose. This ability to create varied and stable frameworks is a reason for the diversity of organic molecules.

Carbon can form single, double, or triple covalent bonds with itself and other elements. Single bonds allow for rotation and flexibility in the molecular chain. Double and triple bonds are more rigid and influence the molecule’s shape. This variety in bonding allows for a greater number of molecular configurations and functions.

Key Carbon Molecules in Life

The chemistry of life is the chemistry of carbon compounds, called organic molecules or biomolecules. These molecules fall into four major classes, which constitute the majority of a cell’s dry mass. They are all built upon a carbon framework that may also incorporate elements like hydrogen, oxygen, nitrogen, and phosphorus.

• Carbohydrates: Serve as a source of energy and as structural components. Composed of carbon, hydrogen, and oxygen, their simplest form is a monosaccharide like glucose (C₆H₁₂O₆). Simple sugars can link to form large polysaccharides, such as starch for energy storage in plants or cellulose for plant cell walls.
• Lipids: Characterized by their hydrophobic nature, lipids include fats, oils, and waxes. Composed of hydrocarbon chains, they are effective for long-term energy storage. Phospholipids form the basic structure of cell membranes, creating a barrier between the cell’s interior and its external environment.
• Proteins: Built from amino acids, proteins are highly diverse and functional. The sequence and folding of amino acid chains create complex structures that determine their function. Proteins act as enzymes, provide structural support, transport substances, and defend against pathogens.
• Nucleic acids: Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) store and transmit genetic information. Their structure is based on a nucleotide, which contains a five-carbon sugar, a phosphate group, and a nitrogenous base. The sequence of bases in DNA encodes the instructions for building an organism, while RNA helps carry out these instructions.

Carbon Molecules in Materials and Industry

Beyond biology, carbon’s bonding properties make it a foundational element in many materials and industrial processes. Numerous daily products are derived from carbon-based molecules. These materials are often based on long chains or networks of carbon atoms with different properties and functions than biological molecules.

Polymers, known as plastics, are a prime example. These materials consist of long chains of repeating smaller molecules called monomers. Polyethylene, used in plastic bags and bottles, is a simple polymer made of repeating ethylene (C₂H₄) units. Other examples like polyvinyl chloride (PVC) and nylon are common in construction, textiles, and consumer goods.

Fossil fuels are hydrocarbons, consisting almost entirely of carbon and hydrogen atoms. Methane (CH₄), propane (C₃H₈), and the octane in gasoline are hydrocarbons of different chain lengths. The energy stored in their covalent bonds is released during combustion, a reaction with oxygen that produces carbon dioxide and water.

The pharmaceutical industry relies on organic chemistry. Most drugs are complex organic molecules designed to interact with specific biological targets. Aspirin (acetylsalicylic acid, C₉H₈O₄) is a synthetic organic compound with therapeutic effects. The arrangement of carbon atoms and functional groups in a drug molecule determines its effectiveness.

Carbon’s Role in the Environment

Carbon cycles through the atmosphere, oceans, land, and living things in what is known as the carbon cycle. This global exchange recycles carbon, making it available for life while also influencing Earth’s climate.

Two significant carbon molecules in the environment are carbon dioxide (CO₂) and methane (CH₄). Carbon dioxide is released through natural processes like respiration and volcanic eruptions and as a byproduct of burning fossil fuels. Photosynthetic organisms absorb CO₂ from the atmosphere, using the carbon to build organic molecules, which forms the base of most food webs.

Carbon dioxide and methane are greenhouse gases that trap heat in the atmosphere. This greenhouse effect is natural and maintains a habitable temperature on Earth. Human activities, particularly the combustion of fossil fuels, have increased the concentration of these gases. This increase disrupts the carbon cycle’s natural balance and is a primary driver of climate change.