Amino acids are classified by the chemical structure of their side chain (R group):
The standard aromatic amino acids possess an aromatic benzene ring in their side chain that strongly absorbs UV light at $280\text{ nm}$: Phenylalanine, Tyrosine (4-hydroxyphenylalanine), and Tryptophan.
Histidine contains an imidazole ring (heterocyclic basic amino acid).
Proline contains a pyrrolidine ring (cyclic imino acid).
Lysine has a positively charged aliphatic amino side chain (diaminomonocarboxylic acid).

In nucleic acids:
DNA (Deoxyribonucleic acid) contains the 5-carbon aldopentose sugar 2'-deoxy-D-ribose ($\text{C}_5\text{H}_{10}\text{O}_4$), which lacks an oxygen atom at the 2' carbon position.
RNA (Ribonucleic acid) contains D-ribose ($\text{C}_5\text{H}_{10}\text{O}_5$), which has a hydroxyl group ($-OH$) at the 2' carbon.

In nucleic acids (DNA and RNA):
Individual mononucleotides are joined together in a continuous polynucleotide strand by covalent $3',5'$-phosphodiester bonds, where a phosphate group forms two ester linkages between the 3'-carbon of one pentose sugar and the 5'-carbon of the adjacent pentose sugar.
A peptide bond is the characteristic covalent bond linking amino acids in proteins.
Glycosidic bonds link nitrogenous bases to sugars (N-glycosidic bond) and monosaccharides in carbohydrates.
(Official Answer Key: Option 2: Phosphodiester bond).

Covalent linkages in biological macromolecules:
Amino acids are polymerised into polypeptides through Peptide bonds (amide linkages, $-\text{CO}-\text{NH}-$), formed via condensation between the $\alpha$-carboxyl group of one amino acid and the $\alpha$-amino group of another with loss of a water molecule.
Glycosidic bonds link monosaccharides in carbohydrates.
Phosphodiester bonds link nucleotides in nucleic acids.
Ester bonds link fatty acids to glycerol in lipids.