There are several atoms or groups of atoms that frequently bond
with carbon. These give distinct properties or functions to the
resulting molecule. Chemists, being very creative people, call
these groups of atoms functional groups. The orientation of
atoms attached to a carbon backbone gives rise to
three-dimensional shapes and functions of biological
molecules.
The following functional groups are commonly involved in
chemical reactions.
Hydroxyl (OH) groups are contained in polar compounds,
such as ethanol (the type of alcohol in beer and other alcoholic
beverages) or glucose.
Carbonyl (C=O) groups are polar groups with a double-bond
between C and O. They are contained in compounds called
aldehydes and ketones. Formaldehyde is an example.
Carboxyl (COOH) groups are polar groups contained in
carboxylic acids. They lose their hydrogen ions to form acids like
acetic acid (vinegar). Fatty acids and amino acids (discussed later in this lecture) have carboxyl
groups.
Amino (NH2) groups are polar groups contained in amino
acids.
Sulfhydryl (SH) groups help stabilize the structure of
proteins. They are contained in the amino acid cysteine.
Phosphate (PO42-) groups store energy that can be passed
from one molecule to another by the transfer of a phosphate
group. Nucleic acids and ATP (adenosine triphosphate) contain
phosphate. More on nucleic acids later in this lecture.