Functional Groups

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 )

Image result for hydroxyl functional group

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)

Functional Properties:

  • 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 )

Image result for carbonyl functional group

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

Functional Properties:

  • 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)


Image result for acetone and propanal chemical formula                                          Image result for propanal chemical formula

The picture to the left is acetone, the simplest ketone. The picture to the right is propanal, an aldehyde.

3rd Chemical Group: Carboxyl ( -COOH )

Image result for carboxyl functional group

Structure: An oxygen atom is double bonded to a carbon atom that is also bonded to an -OH group

Name of Compound: Carboxylic Acid

Functional Properties:

  • Has acidic properties (it donates H+ making it a source of H+) because the covalent bond between oxygen and hydrogen is so polar

Image result for acetic acid to acetate ion

  • Found in cells in the ionized form with a charge of 1- and called a carboxylate ion.

4th Chemical Group: Amino ( –NH₂ )

Image result for amino functional group

Structure: A nitrogen atom bonded to 2 hydrogen atoms and to carbon skeleton

Name of Compound: Amines

Functional Properties:

  • 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
Image result for glycine
The above organic molecule is glycine. Notice that you can see an amine group and a carboxyl group, meaning that glycine is both an amine acid and a carboxylic acid. Compounds with both groups are called amino acids.

5th Chemical Group: Sulfhydryl ( -SH or HS- )

Image result for sulfhydryl group

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


Image result for cysteine
Cysteine is an important amino acid containing a sulfhydryl group.

6th Chemical Group: Phosphate ( –OPO₃²⁻ )

Image result for phosphate group

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

Functional Properties:

  • 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


Image result for glycerol phosphate lewis structure

7th Chemical Group: Methyl ( –CH₃ )

Image result for methyl functional group

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

Functional Properties:

  • Addition of a methyl group to DNA causes the gene to not be expressed


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