THE CHEMISTRY OF LIFE
Functional Groups
Functional groups are very important factors in the creation of biomolecules. Functional groups are defined as “atoms or groups of atoms bonded to the carbon skeleton of a molecule.” Functional groups that are attached to the molecule create unique properties for the molecule depending on the molecular formula of the functional group. Some functional groups can increase the reactivity of the molecule to a certain group of atoms; others affect solubility properties of the molecule or other physical properties. When drawing out functional groups, an R is sometimes used to represent the rest of the molecule, which could either be a long chain of carbons or a ring structure, or any other possible combinations of atoms. In the biological world there are seven different functional groups that play an important role in biomolecules.
The Hydroxyl Group (OH):
The hydroxyl group (a hydrogen single bonded to an oxygen) gives polarity to the molecules by allowing it to form hydrogen bonds with other molecules around it. Mostly all proteins carbohydrates, and nucleic acids contain at least one hydroxyl group. Any molecule that does contain a hydroxyl group can be classified as an alcohol.
The Carbonyl Group (C=O)
The carbonyl group (carbon double bonded to an oxygen) tends to be slightly polar functional groups. Depending on where they are found bonded to the molecule, they can be classified as ketones or aldehydes. Ketones are carbonyl groups that are located in the middle of the molecule, while aldehydes are located at the end of the molecule. In simple sugars, the carbonyl group may react with a hydroxyl group to form a ring structure. Carbonyls are present in simple sugars, some proteins and some nucleotides.
The Carboxyl Group (COOH)
The carboxyl group (carbon bonded to two oxygen atoms and a hydrogen) is an extremely acidic group. This allows the functional group to ionize and releases a H+ atom decreasing the pH levels around it. Molecules that contain a carboxyl group are usually called carboxylic acids for this reason. It is also a highly polar and reactive functional group. The carboxyl group is present in amino acids and proteins.
The Amino Group (NH2)
The amino group (a nitrogen bonded to two hydrogen atoms) is the only functional group that can act as a base by accepting protons. This functional group also increases the polarity and reactivity of a molecule. The amino group allows hydrogen bonding to take place between the hydrogen and other atoms floating around near it. Between this functional group and the carboxyl group, they can bond together in amino acids to make peptide bonds, and important step in making proteins. The group is found in all amino acids, proteins and some nucleotides.
The Sulfhydryl Group (SH)
The sulfhydryl group (sulfur bonded with a hydrogen) is a reactive group that is present in the amino acid cysteine. If two of these groups come together, they are able to form a disulfide bridge strengthening and stabilizing protein structure. This group can also be known as thiols.
The Phosphate Group (OPO3 2-)
The phosphate group (four oxygen bound to a phosphorus atom) is highly polar, reactive, and acidic. It is important in high energy compounds such as ATP and GTP. The phosphate group is present in all nucleotides and phospholipids.
The Methyl Group (CH3)
The methyl group (one carbon bound to three hydrogen atoms) is the only truly nonpolar functional group. The methyl group is found in alcohols, fatty acids, along with some amino acids and nucleotides. If a methyl group is added to a organic molecule, it is called methylation, and can potentially be very bad for the molecule, possibly making the molecule nonfunctional.