BioChem Exam 2 Questions & Answers

which of the following statements concerning protein domains is true? - ANSWERSthey may retain their correct shape even when separated from the protein the structural classification of proteins (based on motifs) is based primarily based on their... - ANSWERSsecondary structure content and arrangement the number of polypeptide chains indicates... - ANSWERSa protein has quaternary structure experiments on denaturation and renaturation after the reduction and reoxidation of the -s- s- bonds in the enzyme ribonuclease (RNase) have shown that... - ANSWERSthe primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure which of the following statements concerning the process of spontaneous folding of proteins is false? - ANSWERSit may be an essentially random process when oxygen binds to a heme- containing protein, the two open coordination bonds of fe2+ are occupied by... - ANSWERSone O2 molecule and one amino acid atom the strength and specificity ("affinity") of binding between two molecules is not dependent on... - ANSWERSconcentration of the 2 molecules two molecules A and B have a Ka = 10^6 M^-1 for AB complex formation. when both molecules are at 10^-5 M (10 uM) the proportion of A and B in an AB complex will be... - ANSWERS90% Two molecules A and B have a KA = 106 M-1 for AB complex formation. When both molecules are at 10-8 M (10 nM) the proportion of A and B in an AB complex will be - ANSWERS10% A protein (P) has a KA = 107 M-1 for a ligand (L). When [L] is at 10-6 M (1 μM) the proportion of P bound by L in a PL complex (the Θ or fraction of binding sites occupied) will be - ANSWERS0.9 In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: - ANSWERShyperbolic hemoglobin - ANSWERSchanges conformation as O2 binds causing a higher affinity for additional O2 binding. O2 binds the oxy or R conformation of Hb. CO2 and BPG bind the deoxy or T conformation. Question 8. It is false that ((18-20 lecture))(((FIND ANSWER!))) - ANSWERSA. a high concentration of CO2 will stimulate BPG binding to Hb. B. a high concentration O2 will stimulate dissociation of BPG and CO2 from Hb. C. a high concentration of CO2 will cause O2 to dissociate from Hb. D. In the presence of BPG a lower concentration of CO2 is required to cause dissociation of O2 from Hb. E. A Hb variant with a lower affinity for BPG binds O2 less tightly than normal Hb (both in the presence of BPG). The fundamental cause of sickle-cell disease is a change in the structure of: (((FIND ANSWER!!!))) ((lecture 18-20)) - ANSWERSA. blood. B. capillaries. C. hemoglobin. D. red cells. E. the heart. Valyl-tRNA synthetase has two amino acid binding sites. One binds valine preferentially, but still binds threonine. The second binds threonine, but not valine by - ANSWERSincluding an additional hydrogen bond acceptor in the binding site. An enzyme can NOT speed up a reaction by - ANSWERSA. the active site providing heat from the environment that raises the energy content of the substrate. In general, enzymes increase the rate of reactions - ANSWERSby reducing the energy of activation If an enzyme is added to a solution where its substrate and products are in equilibrium - ANSWERSE. nothing; the reaction would stay at equilibrium. Concurrent acid and base catalysis - ANSWERSinvolves making reactants better electrophiles and better nucleophiles. Triosephosphate isomerase catalyzes the above reaction and is competitively inhibited by phosphoglycolate by - ANSWERSD. acting as a transition state analog. A mutation in an enzymes active site that increases its affinity for the substrate 100-fold is most likely to - ANSWERSC. reduce the rate of the catalyzed reaction. The catalytic mechanism of serine proteases(4) - ANSWERSA. involves covalent catalysis. B. involves transition state stabilization. C. involves acid-base catalysis. D. involves proximity/orientation. E. involves all of the above. (CORRECT) In the lysozyme active site Glu 35 is protonated while Asp 52 is deprotonated - ANSWERSsince the local environment of Glu 35 is less polar than that of Asp 52. In kinetic analyses of chemical reactions - ANSWERScomparing reactions is simplified by using initial velocities (v0). Enzymes exhibit saturation behavior (become insensitive to more substrate, have a VMax) because - ANSWERSenzymes have a fixed number of active sites where substrate binds. The KM for an enzyme catalyzed reaction - ANSWERSconsistently underestimates the ES binding affinity. Two enzyme preparations have the same KM, but the bacterially expressed enzyme has a 10-fold lower VMax. Question 4. The most likely explanation for this is that - ANSWERS90% of the enzyme expressed in bacteria is inactive. If you were to design an enzyme for a cell, you would give it a KM near the normal cellular substrate concentration - ANSWERSto ma