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BC351
Exam 2
| Question | Answer |
|---|---|
| An alpha helix is stabilized by | Hydrogen bonds between every fourth amino acids in the helix |
| The major reason that antiparallel β-stranded protein structures are more stable than parallel β-stranded structures is that the latter: | have weaker hydrogen bonds laterally between adjacent strands. |
| An average protein will not be denatured by: | iodoacetic acid (C2H3IO2, reacts with reduced cysteines to covalently attach an acetate group to the S). |
| Protein-ligand interactions are formed through | many weak non-covalent interactions |
| Proteins often have regions that show specific, evolutionarily conserved patterns of folding. These regions are called: | motifs or folds. |
| Protein quarternary structure is | Association of two or more tertiary structures |
| Viral capsids often have which type of rotational symmetry? | Icosahedral |
| The functional group likely to be found in a beta-turn is | glycine |
| Leventhal's paradox | is solved by proteins folding in a step-wise, non random fashion. |
| Both gain of function and loss of function mutations in proteins | lead to increased cell proliferation and cancer |
| In an alpha helix | The R-groups are pointed outwards |
| Which of the following is least likely to result in protein denaturation? | Changing the salt concentration |
| Tertiary structure of proteins form | Motifs, domains, and subunits |
| Protein quarternary structure is | Association of two or more tertiary structures |
| Rotational symmetry in proteins | may occur around one or more axes |
| Protein folding | is initially driven by hydrophobic collapse |
| Beta sheets are stabilized by | Hydrogen bonds |
| The interactions of ligands with proteins: | are usually transient. |
| The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are: | generally near each other in sequence. |
| Which of the following statements about oligomeric proteins is false? | All subunits must be identical. |
| Which of the following statements concerning rotational symmetry in proteins is false? | It involves rotation of proteins inside the cell. |
| Functional groups likely to be found on the inside of proteins are | hydrophobic |
| The Ras protein being mutated in a cancer cell so that the protein function is always ON is an example of | a gain of function mutation |
| Separate polypeptide subunits associate to form | quaternary structure |
| A functional group that increases the solubility of organic compounds in water is | all of these functional groups. -NH2. -COH. -SH. -COOH. |
| Highly specific intermolecular interactions | involve as many as 15 to 20 hydrogen bonds. |
| As a protein folds | it begins forming helices and collapsing eventually forming a low energy native folded state |
| A prosthetic group of a protein is a non-protein structure that is | permanently associated with the protein. |
| Protein-ligand binding is dependent on | non-covalent interactions and proper fit |
| When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by | one O2 molecule and one amino acid atom |
| Which of the following is TRUE about 2,3-bisphosphoglycerate? | It does not have a high binding affinity for fetal hemoglobin |
| Mutations in which gene lead to sickle cell disease. | The hemoglobin gene |
| What does an enzyme do? | Catalyze reactions |
| What is a transition state analog? | chemical compounds with a chemical structure that resembles the transition state of a substrate molecule in an enzyme-catalyzed chemical reaction |
| In serine proteases, Histidine 57 | has a pair of electrons available to accept the hydrogen from the serine -OH group, thus coordinating the attack of the peptide bond. |
| Which of the following is FALSE about enzyme catalysts? | They need to be at the same concentration as their substrate |
| Binding energy is | the free energy that is released by the formation of weak interactions between an enzyme and its substrate. |
| Which of the following is an example of a prosthetic protein group | a heme group |
| Anti-cancer drugs have become more specialized as they are designed to fit into the active site of particular enzymes. How do these ligands interact with their specific proteins? | Through noncovalent intermolecular interactions |
| 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 | hyperbolic. |
| Which of the following is TRUE about 2,3-bisphosphoglycerate? | It binds with greater affinity to deoxygenated hemoglobin |
| What is the basic cause of sickle-cell disease? | A change in the structure of hemoglobin |
| In serine proteases, the Serine-195 hydroxyl group | participates in covalent catalysis. |
| If the binding affinity between an enzyme and its substrate is very high, the dissociation constant will be | very low |
| Which of the following statements is true about prosthetic protein groups | they are non-amino acid components of certain proteins that are required for the function of that enzyme or protein |
| Ligands find their binding targets via | random diffusion. |
| In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by | oxygen binding. |
| In the process of catalyzing a reaction, enzymes | affect only ΔG‡ (not ΔG˚). |
| Which one of the following statements is true of enzyme catalysts? | They lower the activation energy for the conversion of substrate to product. |
| Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)? | It increases the affinity of hemoglobin for oxygen. |
| Which has a greater affinity for an enzyme binding site? | A transition state analog |
| Which of these catalytic mechanisms are utilized by serine proteases | covalent catalysis |
| Which of the following is TRUE about enzyme catalysis | An enzyme can interact with it's substrate via transient covalent bonds. |
| When comparing enzymes the KM | is greater for enzymes with lower affinities for a substrate. |
| An assumption made in Michaelis-Menten kinetics is | the enzyme is at a much lower concentration than the substrate |
| What is kcat? | The number of substrate molecules each enzyme site converts to product per unit time. |
| Michaelis-Menten kinetics measures | the reaction rate vs substrate concentration. |
| Cancers can develop drug resistance through | Increased rate of DNA repair |
| Which of the following is TRUE concerning PGP and cancer cells? | PGP is highly expressed in several cellular tissues, breast cancer cells following chemotherapy, and cancer stem cells. |
| How has the structure of PGP been used to circumvent MDR? | Designing PGP inhibitors |
| PGP structure is being used to design | anticancer drugs that do no bind PGP |
| Which of the following is FALSE concerning PGP and cancer cells? | PGP expression is turned off in cancer cells. |
| What is the function of ABC transporters? | They use the energy of ATP binding and hydrolysis to move substances across cellular membranes. |
| Drug resistant cancers can arise through which of the following mechanisms? | Mutations in an enzyme that affect drug binding. |
| The turnover number (kcat) of an enzyme | is a function of VMAX and the total [E]. |
| In kinetic analyses of chemical reactions | comparing reactions is simplified by using initial velocities (v0). |
| Km refers to | the substrate concentration at which the reaction rate is half the Vmax |
| Which of the following is FALSE about enzyme catalysis. | Substrates only interact with the active site of an enzyme via covalent bonds |
| Of the following mechanisms, which would not contribute to enzyme catalysis? | the greater affinity of the active site for binding the substrate relative to the affinity for binding the transition state intermediate |
| When comparing enzymes the KM | is greater for enzymes with lower affinities for a substrate. |
| An assumption of Michaelis-Menten kinetics is | the reaction is irreversible |
| An enzyme has a Vmax of 15μmols/min and and the reaction started with 5μmols of enzyme. What is the kcat of the reaction? | 3/min |
| Drug resistant cancers can arise through which of the following mechanisms? | Mutations in an enzyme that affect drug binding. |
| ABC transporters normally function | to keep toxins from crossing the blood-brain barrier. to protect the genomes of normal stem cells in our bodies. to keep toxins in the mother’s blood from affecting a developing fetus. |
| Which of the following is FALSE concerning PGP and cancer cells? | PGP structure is not useful in fighting MDR. |
| Of the following mechanisms, which would not contribute to enzyme catalysis? | the greater affinity of the active site for binding the substrate relative to the affinity for binding the transition state intermediate |
| The following polypeptide is likely to form (non polar amino acids) | an amphipathic α-helix |
| Thr and/or Leu residues tend to disrupt an α helix when they occur next to each other in a protein because: | steric hindrance occurs between the bulky Thr side chains. |
| An α helix would be destabilized most by: | the presence of two Lys residues near the amino terminus of the α helix. |
| A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-. The sequence is most probably part of a(n): | β turn. |
| The tertiary structure of proteins | is stabilized, but not dictated by disulfide bond formation. |
| Kendrew’s studies of the globular myoglobin structure demonstrated that | the structure was very compact, with virtually no internal space available for water |
| Which of the following statements concerning protein domains is true? | They may retain their correct shape even when separated from the rest of the protein |
| The structural classification of proteins (based on motifs) is based primarily on their | secondary structure content and arrangement. |
| How many proteins in the table above have quaternary structure? | Five. |
| Experiments on denaturation and renaturation after the reduction and reoxidation of the —S—S— bonds in the enzyme ribonuclease (RNase) have shown that | the 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? | It may be an essentially random process |
| the most important contribution to the stability of a proteins conformation appears to be | Entropy increase from the decrease in ordered water molecules forming a solvent shell around it |
| The strength and specificity (affinity) of binding between two molecules is not dependent on | concentration of the two molecules. |
| Two molecules, A and B, have a KA = 106 M-1 for AB complex formation. When both molecules are at 10-5 M (10 μM) the proportion of A and B in an AB complex will be | >90% |
| 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 | <10% |
| 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 | >0.9 |
| 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: | hyperbolic. |
| Hemoglobin | changes conformation as O2 binds causing a higher affinity for additional O2 binding. |
| 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 | including an additional hydrogen bond acceptor in the binding site. |
| An enzyme can NOT speed up a reaction by | the active site providing heat from the environment that raises the energy content of the substrate. |
| In general, enzymes increase the rate of reactions | by reducing the energy of activation |
| If an enzyme is added to a solution where its substrate and products are in equilibrium | nothing; the reaction would stay at equilibrium |
| The catalytic mechanism of serine proteases | involves covalent catalysis. involves transition state stabilization. involves acid-base catalysis. involves proximity/orientation. |
| In the lysozyme active site Glu 35 is protonated while Asp 52 is deprotonated | since the local environment of Glu 35 is less polar than that of Asp 52. |
| A mutation in an enzymes active site that increases its affinity for the substrate 100-fold is most likely to | reduce the rate of the catalyzed reaction |
| Triosephosphate isomerase catalyzes the above reaction and is competitively inhibited by phosphoglycolate by | acting as a transition state analog |
| Concurrent acid and base catalysis | involves making reactants better electrophiles and better nucleophiles. |
| The KM for an enzyme catalyzed reaction | consistently underestimates the ES binding affinity. |
| Two enzyme preparations have the same KM, but the bacterially expressed enzyme has a 10-fold lower VMax. The most likely explanation for this is that | 90% 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 | to make the enzyme activity responsive to changes in cellular substrate concentrations |
| Enzyme kinetic experiments are useful for | comparing different enzymes that catalyze the same reaction. studying the effect of amino acid changes on substrate binding and catalysis. determining if an enzyme inhibitor competes with the substrate for binding. |
| Blood and metastatic cancers | are generally treated using chemotherapy. |
| Drug resistance in cancer cells | can arise through amino acid changes in the target oncoprotein. can arise through increased DNA repair and apoptosis inactivation. can develop through activation of normal detoxification systems. can involve pumps that keep the drug out. |
| Multidrug resistance (MDR) in cancer cells | often arises through expression of Pglycoprotein. |
| P-glycoprotein | functions to keep toxins out of the central nervous system. |
| P-glycoprotein inhibitors | also inhibit cytochrome p450 detoxification. |
Created by:
potato80