Organic compounds are molecules built around a skeleton of carbon atoms, nearly always bonded to hydrogen. They are the molecules made by living things, which is where the name comes from. Simple carbon compounds such as carbon dioxide and carbonates are treated as inorganic.Carbon is ideal as a skeleton because each carbon atom forms four covalent bonds. Carbon atoms can bond to each other to form long chains, branched chains and rings, and to other atoms such as oxygen, nitrogen and hydrogen. This allows an almost endless variety of stable molecules.The four main groups of biological molecules are:• carbohydrates: C, H and O
• lipids: C, H and O (phospholipids also contain P)
• proteins: C, H, O and N (often S)
• nucleic acids: C, H, O, N and PMany biological molecules are polymers: large molecules made of many similar small units called monomers joined together. Monosaccharides are the monomers of polysaccharides, amino acids are the monomers of proteins, and nucleotides are the monomers of nucleic acids. Lipids are large molecules but are not polymers.Monomers are joined by condensation reactions, which release a molecule of water for each bond formed. Polymers are broken down by hydrolysis, which uses a molecule of water to break each bond.Worked example: a polymer made of 50 monomers in an unbranched chain contains 49 bonds between monomers, so 49 water molecules were released when it formed.
• lipids: C, H and O (phospholipids also contain P)
• proteins: C, H, O and N (often S)
• nucleic acids: C, H, O, N and PMany biological molecules are polymers: large molecules made of many similar small units called monomers joined together. Monosaccharides are the monomers of polysaccharides, amino acids are the monomers of proteins, and nucleotides are the monomers of nucleic acids. Lipids are large molecules but are not polymers.Monomers are joined by condensation reactions, which release a molecule of water for each bond formed. Polymers are broken down by hydrolysis, which uses a molecule of water to break each bond.Worked example: a polymer made of 50 monomers in an unbranched chain contains 49 bonds between monomers, so 49 water molecules were released when it formed.