Functional groups

Amino groups (-NH2 or -NH3+ when ionized) (polar)

• accept a proton in solution

Carboxyl group (-COOH or –COO- when ionized) (polar)

• releases a proton in solution

• Carbonyl groups (C=O) (polar)

• sites that link molecules
• aldehydes at the end of a molecule
• ketones in the interior of the molecule

• Hydroxyl groups (-OH) (polar)

• Act as weak acids and can donate H+ in solution

• Phosphate groups (-PO42- ) (polar)

• Have two negative charges when ionized; function in energy transfer or as part of
nucleic acids, also good buffers (accept or donate H+ in solution)

• Sulfhydryl groups (SH) (polar)

• Link together via covalent disulfide bonds (S-S), common in proteins

• Methyl groups (-CH3) (non polar)

• Highly stable, non-reactive
• Do not form hydrogen bonds and do not interact with water
• Hydrophobic