A small number of chemical groups are key to the functioning of biological molecules
The distinctive properties of organic molecules not only depend on the tetravalence and variation of the carbon skeleton, but also on the molecules attached to the carbon skeletons. The chemical groups that affect molecular function by being directly involved in chemical reactions are known as functional groups. Each functional group participates in chemical reactions in a characteristic way, from one organic molecule to another consistently however. The number and arrangement of functional groups help give each molecule its unique properties. The seven functional groups that are most important in biological processes are hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups. I will go into more detail of these seven groups down below in a chart manner.
1st Chemical Group: Hydroxyl ( -OH )
Structure: The structure of hydroxyl is a hydrogen atom is bonded to an oxygen, which in turn is bonded to the carbon skeleton of the organic molecule.
Name of the compound: Alcohols (their specific names usually end in -ol)
- It is polar because the electrons spend more time close to the electronegative oxygen atom
- It can form hydrogen bonds with water molecules. This helps dissolve organic compounds.
2nd Chemical Group: Carbonyl ( C=O )
Structure: A carbon atom double bonded to an oxygen
Name of Compound:
- Ketones- if the carbonyl group is within a carbon skeleton
- Aldehydes- if the carbonyl group is at the end of the carbon skeleton
- A ketone and an aldehyde may be structural isomers with different properties
- Ketones and aldehydes gives rise to two major groups of sugar: aldoses (containing an aldehyde) and ketoses (containing a ketone)
The picture to the left is acetone, the simplest ketone. The picture to the right is propanal, an aldehyde.
3rd Chemical Group: Carboxyl ( -COOH )
Structure: An oxygen atom is double bonded to a carbon atom that is also bonded to an -OH group
Name of Compound: Carboxylic Acid
- Has acidic properties (it donates H+ making it a source of H+) because the covalent bond between oxygen and hydrogen is so polar
- Found in cells in the ionized form with a charge of 1- and called a carboxylate ion.
4th Chemical Group: Amino ( –NH₂ )
Structure: A nitrogen atom bonded to 2 hydrogen atoms and to carbon skeleton
Name of Compound: Amines
- Acts as a base, it accepts H+ from the surrounding solution
- Ionized, with a charge of 1+, under cellular conditions
- Compounds with both amino and carboxyl functional groups are called amino acids
5th Chemical Group: Sulfhydryl ( -SH or HS- )
Structure: A sulfur bonded to atom of hydrogen, resembles hydroxyl group in shape
Name of Compound: Thiols
- Two sulfhydryl groups can form a covalent bond (cross-linking) that helps maintain protein structure
6th Chemical Group: Phosphate ( –OPO₃²⁻ )
Structure: A Phosphorous atom is bonded to 4 oxygen atoms; one oxygen is bonded to carbon skeleton; two oxygens carry negative charges.
Name of Compound: Organic Phosphates
- Contributes negative charge to the molecule of which it is a part (it will contribute a 1- charge when located inside of a chain of phosphates and it will contribute a 2- charge when it is at the end of a molecule)
- Has the potential to react with water, releasing energy
7th Chemical Group: Methyl ( –CH₃ )
Structure: A carbon bonded to 3 hydrogen atoms. Methyl group may be attached to a carbon or to a different atom.
Name of Compound: Methylated Compounds
- Addition of a methyl group to DNA causes the gene to not be expressed