Practice Questions

Heat disrupts weak interactions but usually leaves the covalent peptide backbone intact.

Collagen contains the repeating sequence Gly-X-Y. Glycine occurs every third residue, allowing tight packing of the triple helix.

Quaternary structure exists only in proteins composed of more than one polypeptide chain, such as hemoglobin.

The hydrophobic effect causes non-polar side chains to cluster in the interior, minimizing contact with water and stabilizing the folded structure.

In an α-helix, the carbonyl oxygen of residue i hydrogen bonds with the amide hydrogen of residue i+4, producing the stable helical conformation.

Secondary structures are stabilized by hydrogen bonding between peptide backbone atoms rather than side chains.

Basic amino acids have side chains that accept protons. Lysine contains an ε-amino group that is positively charged at physiological pH.

Peptide bond formation is a dehydration synthesis. The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another, releasing a water molecule (H₂O) and forming a covalent amide linkage (-CO-NH-).

Primary structure is the linear, genetically determined sequence of amino acids in a polypeptide chain, held together by covalent peptide bonds. This sequence dictates all higher levels of protein structure.

Complete acid hydrolysis (e.g., 6M HCl at 110°C for 24 hours) cleaves all peptide bonds in a protein, releasing the constituent free amino acids. Partial hydrolysis yields smaller peptides (di-, tri-, and oligopeptides).