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Functional Groups

Functional groups are collections of several different groups of atoms, within molecules, that have specific characteristics and play a role in the formation of key biomolecules, such as nucleic acids and proteins.
Because of the millions of compounds that can be created through carbon bonding, scientists use an organization system to classify organic compounds. This system involves both identifying and defining functional groups in an organic compound. A functional group is a group of atoms with specific physical, chemical, and reactivity properties. Not only are the groups commonly found attached to the carbon backbone of organic molecules, but each organic molecule has its own distinctive set of functional groups that allow the molecule to have specific properties and functions in the cell. Specifically, functional groups play a role in forming key biomolecules that a cell relies on for function and survival. For example, molecules such as DNA, proteins, carbohydrates, and lipids can be differentiated from each other by observing key functional groups in each molecule. DNA has an oxygen atom bonded to a hydrogen atom or hydroxyl group, which is a structure containing the chemical formula OH, and carbohydrates contain both a hydroxyl and aldehyde group, which is a structure that contains the chemical formula CHO, a carbon atom double bonded to an oxygen atom. A hydrocarbon is an organic compound that contains only carbon-carbon and carbon-hydrogen bonds. These compounds are the main component of petroleum and natural gas. Take, for example, methane, CH4. The methane molecule is the simplest hydrocarbon, where the central carbon atom forms nonpolar covalent bonds with four different hydrogen atoms. Because of this atomic arrangement, all valence electron shells of the hydrogen and carbon atoms are filled. Functional groups are usually classified as hydrophilic (water loving) or hydrophobic (water fearing), depending upon each group's polarity, which refers to the distribution of electric charge between atoms in a molecule or between two or more molecules. Hydrogen is nonpolar, as is the methyl group (CH3). The hydroxyl (OH) group, carbonyl (CO) group (a functional group with a carbon atom double bonded to an oxygen atom), and sulfhydryl (SH) group (a functional group that contains a sulfur atom bonded to a hydrogen atom) are all polar, which means there is an unequal sharing of valence electrons between these covalently bonded atoms. The carboxyl and phosphate groups are acidic, which indicates that they release hydrogen (H) ions in solution, while the amino group is basic, partially separating in solution to release hydroxide (OH) ions.
Common Functional Groups Found in Biomolecules
Name Functional Group Compounds
Amino acids, proteins
Ketones, aldehydes, carboxylic acids, amides
Carboxylic acid
Amino acids, proteins, fatty acids
Lipids, nucleic acids
Disaccharides, polysaccharides, lipids
Alcohols, monosaccharides, amino acids, nucleic acids
Methylated compounds, such as methyl alcohols and methyl esters
Nucleic acids, phospholipids, ATP
Amino acids, proteins

Functional groups can be found in many organic molecules, and each has specific chemical properties. The R in each diagram represents the location where the functional group attaches to the hydrocarbon chain.