UNIT 1 UNE CHEM 1005 EXAM QUESTIONS AND ANSWERS

UNIT 1 UNE CHEM 1005 EXAM QUESTIONS AND ANSWERS Hemoglobin binds oxygen with a greater affinity in the: R state Hemoglobin bound to heme is termed a holoprotein. The heme or porphoryin ring is required for oxygen binding and it is termed a: prosthetic group Alpha helices and beta sheets are primarily stabilized by: H bonding Ligases are a class of enzymes characterized by their ability to: synthesize bonds between carbon atoms and an additional atom that is involved in the cleavage of a high energy bond. An enzyme inhibitor that increases the Km but does not change the Vmax is classified as: competitive inhibitor Cleavage of fructose 1, 6 bisphosphate to dihydroxyacetone and glyceraldehyde 3-phosphate is achieved by what class of enzymes: lyase Enzymes reduce the activation energy for a reaction. All enzymes do this by: providing an active site most complementary the transition state, Enzymes help to reduce the activation energy of a reaction by stabilizing high energy intermediates. By have a flexible active site that is highly complementary to the transition state of a substrate this is most readily achieved. The activity of an enzyme is increased when the enzyme is phosphorylated on an exposed tyrosine residue. Phosphorylation of this amino acid is classified as which of the following? covalent modification, Phosphorylation is a covlanet modification to an enzyme that can increase or decrease the activity of an enzyme. Under low energy conditions, AMP will bind to phosphofructokinase I and glycogen phosphorylase. This is an example of which of the follow types of enzyme regulation? allosteric activation Which of the following is an example of enzyme regulation through covalent modification? Phosphorylation of muscle glycogen phosphorylase Movement of ammonia from an amino acid to an alpha-keto acid involves a family of enzymes best categorized as: Transferases An alpha-helical arrangement of amino acids is considered to be part of what level of protein structure? secondary structure of the protein An example of enzyme activation by cleavage is best illustrated by which of the following? activation of chymotrypsinogen to chymotrypsin Coenzymes are complex nonprotein molecules that participate in catalysis by providing functional groups that form a covalent intermediate between the enzyme and the substrate. Which of the following is an example of a coenzyme that participates in an activation-transfer reaction? Thiamaine pyrophosphate (TPP) Motifs are common structural elements that retain a particular function within the protien. Which of the following is an example of a protein motif? An arrangment of β-strands connected by α - helicies (βαβαβ) What is an allosteric activator? a. binds and puts active site in optimal configuration which favors substrate binding, higher efficiency b. noncovalent, so reversible c. also dependent on enzyme concentration What is an allosteric inhibitor? a. binds to enzyme and changes shape of active site so substrate cannot bind and enzyme is turned off b. binding through noncovalent interactions so are reversible c. whether or not they bind to enzyme depends on concentration d. the mechanism behind feedback inhibition Competitive inhibitors? Compete with substrate for binding at enzyme's substrate recognition site. This increases Km because it increases the concentration of substrate needed to saturate the enzyme, but no change to Vmax. Noncompetitive inhibitor Does not compete with substrate for binding at the enzyme's substrate recognition site. Lowers concentration of active enzyme so Vmax decreases, but no change to Km. Protein kinases phosphorylate proteins only at a certain hydroxyl groups on amino acid side chains. All contain side chain hydroxyl groups: Serine, Threonine, Tyrosine Globular protein characteristics Tertiary structure is formed by hydrophobic and electrostatic interactions between amino acid side chains and by hydrogen bonds between the peptide bonds. hydrophobic inside, hydrophilic outside. T/F Heme is not a coenzyme True Competitive inhibitor competes with a substrate for binding at enzyme active site. This interaction causes which of the following changes in enzyme activity? Addition of competitive inhibitor will not impact Vmax of enzyme. Enzymes facilitate reactions through this mechanism Decrease activation energy Allosteric activator will increase enzyme activity through this mechanism Binding the enzyme and keeping it in R conformation. Hemoglobin has the ability to display cooperative binding. The property of cooperative binding is only displayed by proteins that have __________________ structure. quaternary Quaternary structure increases protein stability, enables a protein to exhibit cooperative binding or to form binding sites with a high affinity for large molecules. All of the following are considered coenzymes except: Heme.Heme is not considered a coenzyme. It is a prosthetic group within hemoglobin that binds iron. The heme ring itself is not part of oxygen binding. Under conditions when glucose is high, hexokinase will be more active then glucokinase kinase. This is due to which of the following rationales? Glucokinase has a higher Km than hexokinase You would expect all of the following except to be within an alpha helix in a transmembrane domain proline.Explanation: Proline is considered a 'helix breaker' and would not be found in an alpha helix; all other residues are nonpolar hydrophobic and could reside in a transmemebrane domain Hemoglobin bound to heme is termed holoprotein Explanation: Hemoglobin or myoglobin bound to the heme prosthetic group is termed a holoprotein. Without the heme the protein is termed an apoprotein Covalent catalysis is used by many enzymes to cleave peptide bonds. All of the following amino acid side chains may help in this reaction except valine. Valine is a nonpolar amino acid and lacks a nucleophile to facilitate the generation of a catalyst- substrate covalent bond Chymotrypsin is a protease that cleaves peptide bonds. It is characterized as which of the following classes of enzymes? Hydrolases Hemoglobin is a large goblin protein that consists of 4 subunits. Each subunit is composed of 7 -alpha helicies. The interactions of those helical domains with each other within a single subunit is best described as tertiary structure of the protein Myoglobin: Both bind oxygenHemoglobin travels in the blood inside a red blood cell to deliver oxygen to tissues.Myoglobin remains in the heart and skeletal muscle cells to bind oxygen released by hemoglobin.Homologous proteins; they have similar primary sequencesLike all proteins, the tertiary and quaternary structures are stabilized by hydrophobic interaction, hydrogenbonds, and salt bonds Hemoglobin (Hb) Hb is a heterotetramer (four "mers" and at least one monomer is different from the others).Hb is composed of 2 alpha and 2 beta subunits.Each subunit has its own heme; hemoglobin can bind 4 oxygen moleculesCooperativity: When O2 binds to the Fe2+ at one of the Hb binding sites, it pulls on the histidine, which pulls onthe alpha helix, changing the conformation of the globin slightly. This slight movement changes theconformation of the other three chains in the Hb.When oxygen binds to one heme, the other hemes are more likely to bind a second molecule of oxygen.Hemoglobin does not by oxygen as strongly as myglobin sigmoidal bindingWhen oxygen is released from hemoglobin, the loss of one molecule of oxygen facilitates the loss of additionaloxygen moleculeso This is the reverse of positive cooperativity.Hemoglobin can exist in two