AP Biology Functional Groups

All 7 Functional Groups in Biology

Hydroxyl group

A polar functional group consisting of a hydrogen atom bonded to an oxygen atom.

Structure: $-\text{OH}$

It forms hydrogen bonds with water and helps dissolve organic compounds such as sugars.

Carbonyl group

A functional group consisting of a carbon atom double-bonded to an oxygen atom.

Structure: $>\text{C}=\text{O}$

Found in aldehydes ($-\text{CHO}$) at the end of a carbon skeleton and ketones within a carbon skeleton.

Carboxyl group

A functional group consisting of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group.

Structure: $-\text{COOH}$

It acts as an acid by donating $H^+$ ions to form an ionized carboxylate group ($-\text{COO}^-$).

Amino group

A functional group consisting of a nitrogen atom bonded to two hydrogen atoms.

Structure: $-\text{NH}_2$

It acts as a base by picking up an $H^+$ ion from the surrounding solution to form an ionized amino group ($-\text{NH}_3^+$).

Sulfhydryl group

A functional group consisting of a sulfur atom bonded to a hydrogen atom.

Structure: $-\text{SH}$

Two sulfhydryl groups can react to form a covalent disulfide cross-link ($-\text{S}-\text{S}-$) that stabilizes protein structure.

Phosphate group

A functional group consisting of a phosphorus atom bonded to four oxygen atoms.

Structure: $-\text{OPO}_3^{2-}$

It contributes negative charge to the molecule and allows energy storage and transfer (e.g., in ATP).

Methyl group

A nonpolar functional group consisting of a carbon atom bonded to three hydrogen atoms.

Structure: $-\text{CH}_3$

It affects the expression of genes when bound to DNA or proteins, and alters molecular shape and function.