The physical structure of a protein often reflects and affects its function.
(a) Describe THREE types of chemical bonds/interactions found in proteins. For each type, describe
its role in determining protein structure. (6 points; 1 point for bond/interaction description,
1 point for description of role)
Bond/interaction Description Role associated to bond/interaction
Covalent/
peptide
sharing electrons OR
linking amino acids together
amino acid sequence OR primary structure
(no credit for chain or polypeptide alone)
Disulfide/
covalent
disulfide, S–S bond (bridges);
sulfur-containing R group bonding
tertiary or quaternary structure
Hydrogen H–O or H–N interactions α helix, β sheet; secondary, tertiary, or
quaternary structure
van der Waals unequal electron clouds in R group;
dipole moments
tertiary or quaternary structure
Hydrophobic nonpolar R groups tertiary or quaternary structure
Ionic charged R groups tertiary or quaternary structure
(b) Discuss how the structure of a protein affects the function of TWO of the following. (3 points
maximum)
Muscle contraction (1 point for each bullet; 2 points maximum)
• Actin (thin filaments) and myosin; cross-bridges OR filamentous proteins slide past each other.
• Troponin/tropomyosin interaction blocks binding of myosin to actin.
• Ca2+ changes troponin shape/binding of troponin-tropomyosin to actin altered.
• ATP/ADP changes myosin structure.
Regulation of enzyme activity (2 points maximum)
• Shape change caused by (1 point for each bullet)
o Binding of allosteric or noncompetitive inhibitor.
o Binding of allosteric activator.
o Feedback control.
o pH or temperature changes.
o Cleavage of pre-enzyme (e. g., zymogen).
o Cooperativity; coenzymes; cofactors.
o Covalent modification (e. g., phosphorylation).
• Competitive inhibitors binding in the active site prevent substrate binding.
NOTE: The active site regulating enzyme activity is not enough to earn a point.