Proteins — practice questions

1. The primary structure is the specific linear sequence of amino acids in the polypeptide chain.
2. This sequence dictates the R-groups present and their specific positions, which then determine the types and locations of interactions (e.g., hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions) that form during the folding process.
3. These interactions lead to the unique and specific three-dimensional tertiary structure. This precise 3D shape, particularly the presence of an active site or binding site, is essential for the protein to carry out its specific biological function (e.g., enzyme catalysis, hormone binding).

1. Sum the Mr of all individual amino acids: Mr(total) = 75 (Gly) + 89 (Ala) + 117 (Val) + 121 (Cys) + 75 (Gly) = 477
2. Determine the number of peptide bonds formed: For 'n' amino acids, 'n-1' peptide bonds are formed. In this case, 5 amino acids link together, forming 5 - 1 = 4 peptide bonds.
3. Account for the water molecules lost during condensation: Each peptide bond is formed via a condensation reaction, releasing one molecule of water. Therefore, 4 water molecules are released.
4. Calculate the total mass of water removed: Mass of water removed = 4 × Mr(H₂O) = 4 × 18 = 72
5. Calculate the final Mr of the polypeptide: Mr(polypeptide) = Mr(total amino acids) - Mr(water removed) Mr(polypeptide) = 477 - 72 = 405

Final Answer: The relative molecular mass of the polypeptide is 405.