BCH 461 EXAM QUESTIONS AND ANSWERS

What are the four levels of protein structure? - Answer-primary, secondary, tertiary, quaternary primary structure - Answer-The first level of protein structure; the specific sequence of amino acids making up a polypeptide chain. secondary structure - Answer-The second level of protein structure; the regular local patterns of coils or folds of a polypeptide chain. tertiary structure - Answer-The third level of protein structure; the overall, three-dimensional shape of a polypeptide due to interactions of the R groups of the amino acids making up the chain. quarternary structure - Answer-The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits. What is the structure of a peptide bond? - Answer-Planar properties of peptide bond - Answer-the peptide bond is the amide linkage between the carboxylic acid, one amino acid, and the amine of another amino acid. a. Partial double bond character b. Rigid and planar because of lack of rotation around the peptide bond c. Trans configuration - minimizes steric hindrance d. Uncharged but polar - dipole moment exists due to separation of charge Ramachandran plot - Answer-Shows favorable phi-psi angle combinations. 3 main "wells" for α-helices, ß-sheets, and left-handed α-helices. Displays allowed regions of protein folding space. It is a plot of Phi and Psi angles Ramachandran Principle - Answer-alpha helices, beta strands, and turns are the most likely conformations for a polypeptide chain to adopt, because most other conformations are impossible due to steric collisions between atoms. phi angle - Answer-In peptides, the angle of the bond between the alpha carbon and the amine group psi angle - Answer-ψ; angle between alpha carbon and carboxyl carbon The number of angles in an isolated amino acid (not in the polypeptide chain) is - Answer-none; The phi angle involves the carboxyl carbon of the previous amino acid in a p