Carbon is all around us. This unique atom is the basic building block of life, and its compounds form solids, liquids, or gases. Carbon helps form the bodies of living organisms; it dissolves in the ocean; mixes in the atmosphere; and can be stored in the crust of the planet.

“The large molecules necessary for life that are built from smaller organic molecules are called biological macromolecules. There are four major classes of biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids)… Biological macromolecules are organic, meaning that they contain carbon.” It further notes: “It is often said that life is ‘carbon-based.’ This means that carbon atoms, bonded to other carbon atoms or other elements, form the fundamental components of many, if not most, of the molecules found uniquely in living things… carbon certainly qualifies as the ‘foundation’ element for molecules in living things.”

In discussing life’s chemistry, the review notes that terrestrial biochemistry is "carbon-based," relying on organic molecules constructed on carbon skeletons. It explains that carbon’s ability to form stable covalent bonds with itself and with other elements, combined with its capacity for forming a wide variety of functional groups, provides the structural diversity required for self-replicating molecules and metabolic networks associated with life.

The article describes proteins, enzymes, carbohydrates, lipids, and nucleic acids as “fundamental macromolecules essential for life.” It states: “These biomolecules are organic compounds primarily composed of carbon and play crucial roles in various biological processes.” Later it generalizes: “All biochemical macromolecules are organic compounds, their essential molecular structure being composed of carbon atoms.”

The paper explains that “Deoxyribonucleic acid (DNA) is one of the most important molecules in living cells. It encodes the instruction manual for life.” DNA is described as “a polymer made of monomeric units called nucleotides… a nucleotide comprises a 5‑carbon sugar, deoxyribose, a nitrogenous base and one or more phosphate groups.” It notes similarly that “The building blocks [of RNA] are nucleotides containing the 5‑carbon sugar ribose, a phosphate and a nitrogenous base.”

The Royal Society of Chemistry describes carbon as a non-metal with four electrons in its outer shell, which "allows it to form four covalent bonds". It notes that carbon’s ability to form strong bonds with itself leads to long chains and rings, and that "this catenation is the reason there are so many different organic compounds". The entry also points out that these organic compounds are central to living organisms, forming structures such as proteins, carbohydrates, and DNA.

Khan Academy notes that organisms are made up of biomolecules—“carbohydrates, proteins, nucleic acids, and lipids”—and that these are “organic, meaning their chemical structures always include the element carbon.” It also states: “Nucleic acids are biomolecules made up of carbon (C)… DNA encodes an organism’s genetic information… Lipids are organic compounds made up of carbon… Carbohydrates are sugars and sugar polymers made up of carbon.”

The overview notes that carbon’s "tetravalent nature allows carbon to form four bonds, leading to the creation of chains, branched structures, and rings, contributing to the vast diversity" of carbon compounds. It emphasizes that the strength and stability of C–C bonds enable extensive catenation, and that this underpins the huge variety of organic molecules, which include the structural and functional molecules found in living organisms.

Carbon is the fourth most abundant element in the universe and is the building block of life on Earth. The fundamental component for the major biological macromolecules is carbon, and its covalent bonding properties make it the backbone of these molecules.

These university lecture notes describe major biological molecules as polymers constructed from covalent binding of monomers: “Biological molecules are polymers, constructed from the covalent binding of smaller molecules called monomers.” For carbohydrates, they give the general formula “Cn(H2O)n” and list roles such as “Source of stored energy… Transport stored energy… Carbon skeletons that can be rearranged to form new molecules,” emphasizing that the carbohydrate backbone provides a carbon framework. Lipids are described as “nonpolar hydrocarbons,” and nucleic acids as “polymers specialized for the storage, transmission, and use of genetic information.”

The article explains that "carbon atoms form the backbone of organic molecules because of their unique ability to create stable, versatile and diverse structures through covalent bonding." It notes: "Unlike most elements, carbon can form four strong covalent bonds, allowing it to connect with up to four other atoms simultaneously. This tetravalency gives carbon extraordinary flexibility, enabling the formation of chains, rings, branches and complex three-dimensional frameworks." It also stresses carbon’s "ability to undergo catenation, the process of bonding with itself to form long, stable chains" and compares it with silicon, stating that Si–Si bonds are weaker and limit structural possibilities, underscoring why carbon is especially suited for life’s complex molecules.

The explanation states that "carbon has four valence electrons, allowing it to form up to four strong covalent bonds. This tetravalency gives rise to an immense variety of bonding structures—single, double, and triple bonds—which contribute to molecular complexity." It continues: "Consider the concept of catenation, which refers to the ability of carbon to form long chains and complex branched structures. This property is fundamental to the formation of the diverse array of organic compounds." The text concludes that carbon compounds "form the backbone of essential biological macromolecules such as proteins, carbohydrates, lipids, and nucleic acids, underscoring its pivotal role in life's chemistry."

All life on planet Earth is bound by one common factor: carbon. Biomolecules such as proteins, DNA, and carbohydrates are all carbon-based molecules, with carbon atoms serving as the backbone of these structures.

Carbon is the basic structural element of life because it can form four bonds and build large, complex molecules. That makes it the foundation for molecules such as DNA, proteins, carbohydrates, and fats.

The video introduces carbohydrates, lipids, proteins, and nucleic acids and notes: “Now these molecules are all classed as organic which just means that they contain carbon.” It explains a key property of carbon: “one of the special things about carbon is that it can form four covalent bonds either with other carbon atoms or with different elements… These bonds can be either single bonds or double bonds, giving carbon the flexibility to form a wide variety of complex structures.”

In summarizing the elemental composition of biomolecules, the video highlights a mnemonic: “a mnemonic known as CHO, CHO, CHON, CHONP – although it’s ‘chomp’ with an ‘n’ – to help remember the C for carbon, H for hydrogen, O for oxygen, N for nitrogen, and P for phosphorous.” This mnemonic reflects that carbohydrates and lipids (CHO), proteins (CHON), and nucleic acids (CHONP) all include carbon as a core element.

In proteins, each amino acid monomer includes a central (alpha) carbon atom bonded to an amino group, a carboxyl group, a hydrogen, and a variable side chain; linking many amino acids forms a polypeptide with a continuous carbon backbone. In lipids such as fatty acids and triglycerides, long chains of carbon atoms bonded to hydrogen (hydrocarbon chains) form the core of the molecules, making carbon-based chains responsible for energy storage and hydrophobic properties.

Carbon is essential to life due to its unique chemical properties, which serve as a foundational element for organic molecules and biochemistry. Carbon is crucial because it helps form complex molecules such as DNA and structural proteins that sustain life on Earth.

Carbon compounds are central to life on earth. They form the building blocks of proteins and other biological structures.