In living organisms, there are four important building block macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Organic molecules at a minimum has carbon and hydrogen. All four of these macromolecules are organic molecules. Biological macromolecules can be monomers or polymers (or neither). A monomer is a single unit and can be attached to other monomers covalently to form the polymer. Polymers of the biological macromolecules can be synthesized through dehydration synthesis, which is when water is taken out and a covalent bond is formed between two monomers. Polymers of the biological macromolecules can also be broken down through hydrolysis, which is when water is used to break the covalent bond between two monomers.
Carbohydrates are sugars. They have a 1:2:1 ratio of carbon:hydrogen: oxygen. Some common monomeric carbohydrates are glucose, fructose, and galactose. These are also called monosaccharides because they contain one single sugar ring. Glucose, fructose, and galactose have the composition and are thus called isomers, because they have the same chemical composition but a different arrangement of the atoms. They are also called hexose sugars because they have 6 carbons. There are also pentose and triose sugars, which have 5 carbon molecules and 3 carbon molecules in the monomers, respectively.
Through dehydration synthesis, two monosaccharides combine to form a disaccharide, which consists of two monosaccharides. The bond between two monosaccharides is called a glycosidic bond. Two glucose molecules with a glycosidic bond between them is called maltose. A fructose molecule and glucose molecule with a glycosidic bond between them is called sucrose. A glucose molecule and galactose molecule with a glycosidic bond between them is called lactose.
Sugars may be broken into two categories: aldoses and ketoses. If one is to write the carbon skeleton diagram (rather than the ring diagram) of the carbohydrate, aldoses have the carbonyl group at the end of the carbon skeleton, but ketoses have the carbonyl group within the carbon skeleton. For example, glucose and galactose are aldoses but fructose is a ketose.