Functional groups are covalently bonded sets of atoms that affect the properties of a molecule. Molecules containing the same functional groups often exhibit similar properties and undergo similar reactions. Naming functional groups allows for the quick identification of the atoms in a molecule, which is useful in organic chemistry and biochemistry. Hydrocarbons are the basis of organic molecules and contain varying numbers of carbon and hydrogen atoms. These include alkanes, alkenes, and alkynes. Carbon atoms in alkanes are linked together by single bonds, whereas alkenes and alkynes contain double or triple bonds, respectively. Hydrocarbons can form closed rings. If the ring contains only single bonds, it is called a cycloalkane. If the carbons are linked together by alternating single and double bonds, it is called an aromatic ring or an aryl group. One of the simplest non-carbon containing groups is the hydroxyl group which contains an oxygen atom and a hydrogen atom. It is an important constituent of several compounds, such as methanol, water, and carbohydrates. Another category of functional groups is the carbonyl groups, which contain a carbon and an oxygen linked together by a double bond. Carbonyl containing groups include functional groups such as aldehydes, ketones, esters, and carboxyl groups. Aldehydes have hydrogen and a variable or R group attached to a carbonyl, while ketones have two variable groups. R groups often represent hydrocarbons but can be other groups or atoms. Aldehydes and ketones are key functional groups in carbohydrates Esters consist of a carbonyl group flanked by a R group and an oxygen, while carboxylic acids, or carboxyl groups, are flanked by an R group and an alcohol. Lipids contain esters, and amino acids contain carboxylic acids. Amino acids also have another common functional group called an amine or amino group. An amine has a nitrogen with a lone pair linked to a combination of hydrogens and R groups. Amino acids are the building blocks of proteins. A phosphate group is a phosphorus bonded to four oxygens and is commonly found in DNA, the genetic material of all living organisms. It can also be attached to proteins to alter their function.