1953894
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Test por MatthewEllis96, actualizado hace más de 1 año
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Creado por MatthewEllis96
hace más de 9 años
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Pregunta 1
Pregunta
The Michaelis-Menton model:
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Is based on the assumption that a transition state is formed in the enzyme active site.
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Is based on the assumption that an enzyme catalysed reaction is mediated at the active site of an enzyme.
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Is based on the assumption that a biochemical reaction is at equilibrium.
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Is based on the assumption that a biochemical reaction occurs at a steady state.
Pregunta 2
Pregunta
The Michaelis-Menton constant, Km:
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Is associated with the maximum enzyme activity observed when the all active sites in an enzyme are saturated with substrate.
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Is associated with the number of substrate molecules reacted on by an enzyme molecule per unit time.
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Is associated with the affinity of an enzyme for a specific substrate.
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Is associated with the selectivity of an enzyme for different substrates.
Pregunta 3
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In enzyme kinetics, the ratio of constants kcat/Km:
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Is a measure of the rate of acceleration carried out by the enzyme.
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For a given enzyme is independent of the substrate used.
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Has units of concentration.
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Gives an idea of the enzymes catalytic efficiency.
Pregunta 4
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The Km/Kcat ratio:
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Is associated with the maximum enzyme activity observed when the all active sites in an enzyme are saturated with substrate.
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Is associated with the number of substrate molecules reacted on by an enzyme molecule per unit time.
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Is associated with the affinity of an enzyme for a specific substrate.
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Is associated with the selectivity of an enzyme for different substrates.
Pregunta 5
Pregunta
In enzyme catalysis, the term ‘approximation’ refers to:
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A catalytic strategy facilitating transition state formation through covalent bond formation between the substrate and enzyme active site.
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A catalytic strategy facilitating transition state formation through hydrogen bond formation and electrostatic bond formation between the substrate and enzyme active site.
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A catalytic strategy facilitating transition state formation through interaction involving metal ions and substrate in the enzyme active site.
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A catalytic strategy facilitating transition state formation through direct transfer of a proton to or from the substrate in the enzyme active site.
Pregunta 6
Pregunta
Consider an enzyme that shows Michaelis-Menten kinetics where:
v0 = Vmax . [S] / (Km + [S])
If a substrate, S, is present at a concentration of 8 mM, and Km is 4 mM, the rate of reaction (v0) measured will be:
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Half of Vmax
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Two thirds of Vmax
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Double Vmax
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Three times Vmax
Pregunta 7
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Koshland’s induced fit model for enzyme-substrate complex formation:
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May explain why enzymes have particular substrate specificity.
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May explain why enzymes are able to catalyse chemical reactions that cannot be facilitated in any other way
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May explain why enzymes increase the rate of a reaction by reduction of the activation energy change for the reaction
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May explain why enzymes can effectively reduce the loss of energy from a chemical reaction as heat
Pregunta 8
Pregunta
Enzymes:
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are chemically altered at the end of their reaction
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are involved in changing the equilibrium constant of the reaction that they catalyse
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bind their substrates at their active site(s)
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increase the activation energy of the reaction they catalyse
Pregunta 9
Pregunta
The Michaelis constant, Km:
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Is a measure of the rate acceleration caused by the enzyme
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For a given enzyme is independent of the substrate used
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Has units of concentration
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Gives an idea of the enzyme’s catalytic efficiency
Pregunta 10
Pregunta
The Vmax of an enzyme catalysed reaction:
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Is altered when a competitive inhibitor is present
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Can be determined from the intercept on the x-axis of a Lineweaver-Burk plot
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Is the maximum rate at which the enzyme can convert substrate into product
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Has units of concentration
Pregunta 11
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Proteosome-mediated proteolysis:
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Is controlled by serine protease enzymes.
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Is a key part of the control mechanism in the eukaryote cell cycle
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Is a key part of the control mechanism in the prokaryote cell cycle
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Is controlled by ubiquinone activating enzymes.
Pregunta 12
Pregunta
The Alanine Cycle:
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Is completely located in the mitochondrial matrix.
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Facilitates transport of ammonia produced in the liver to the muscles where it can be used in anabolic processes - preventing the exposure of free ammonium to other components of eukaryote tissues.
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Facilitates transport of ammonia produced in the muscles to the liver where it can be effectively removed from the body - preventing the exposure of free ammonium to other components of eukaryote tissues.
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Is located in the cell membrane of muscle cells.
Pregunta 13
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The transition state for an enzyme-catalysed reaction:
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Describes the way the substrate interacts with the enzyme.
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Descibes the protein tertiary structure when the enzyme substrate is converted to a product.
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Describes the form the substrate takes that facilitates the formation of a low energy intermediate during the catalytic cycle.
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Describes an intermediate in the catalytic cycle that is produced in order to minimise the activation energy for the reaction.
Pregunta 14
Pregunta
An enzyme has the following kinetic parameters: Km = 20mM, Vmax= 50 mM.s-1
Using the equation: v0=Vmax.[S]/Km+[S]
When the rate, v0, is measured at 30 mM.s-1; the substrate concentration, [S] will be:
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15 mM
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30 mM
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45 mM
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60 mM
Pregunta 15
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The value of ΔG0’ for an enzyme catalysed reaction:
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Will always be negative if an enzyme catalysed reaction proceeds spontaneously.
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Will always be positive if an enzyme catalysed reaction proceeds spontaneously.
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Will always be equal to the ΔG value for a reaction where both the reactants and products have an equal concentration.
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Will only apply to a reaction occurring if the pH = 7.0 in aqueous solution.
Pregunta 16
Pregunta
An abzyme is:
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An enzyme that is protein-engineered to work like an antibody.
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An antibody that is protein-engineered to work like an enzyme.
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An enzyme that has high affinity for a transition state analogue.
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An antibody that has high affinity for a transition state analogue.
Pregunta 17
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An oxyanion hole is:
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A region of the enzyme active site that facilitates binding of positively charged substrates through their association with oxygen-containing amino-acid side chains in the enzyme.
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A region of the enzyme active site that facilitates binding of negatively charged substrates through their association with oxygen-containing amino- acid side chains in the enzyme.
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A region of the active site that facilitates binding of positively charged oxygen- containing groups present in a substrate.
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A region of the active site that facilitates binding of negatively charged oxygen-containing groups present in a substrate.
Pregunta 18
Pregunta
Which of the following catalytic strategies is not employed by the enzyme chymotrypsin:
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Approximation.
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Acid-base catalysis.
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Metal-ion catalysis.
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Covalent catalysis.
Pregunta 19
Pregunta
The urea cycle:
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Is completely located in the mitochondrial matrix – preventing the exposure of free ammonium to other components of the eukaryote cell.
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Allows free ammonia obtained directly from deamination of glutamate to be converted to urea – preventing the exposure of free ammonium to other components of the eukaryote cell.
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Allows free ammonia obtained directly from deamination of tryptophan to be converted to urea – preventing the exposure of free ammonium to other components of the eukaryote cell.
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Is completely located in the cytoplasm of the cell – preventing the exposure of free ammonium to other components of the eukaryote cell.
Pregunta 20
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An end-product can act to inhibit an enzyme by binding at the:
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Active site
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Activation site
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Allosteric site
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Transitional site
Pregunta 21
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Serine proteases:
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Are proteases that hydrolyse polypeptides with serine in the F1 position
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Are proteases that are found in the cytoplasm of all cells
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Utilise a serine residue at the active site to facilitate substrate binding
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Utilise a serine residue at the active site to facilitate cleavage of peptide bonds
Pregunta 22
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In acid-base catalysis:
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An acidic- or basic- amino acid in the active site of an enzyme facilitates transition state formation by hydrogen abstraction from an appropriate substrate.
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An acid- or basic- substrate in the active site of an enzyme facilitates transition state formation by hydrogen abstraction from a catalytic amino acid in the active site.
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Both are correct.
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Neither are correct.
Pregunta 23
Pregunta
The protein ubiquitin:
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Can be covalently linked to proteins via the N-terminus glycine residue.
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Is a polypeptide.
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Is an essential component of eukaryote respiratory chains.
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Can be covalently linked to proteins via isopeptide bond formation.
Pregunta 24
Pregunta
If the ΔG°′ of the reaction Malate → Oxaloacetate is +30 kJ/mol, what will happen in the presence of malate dehydrogenase under standard conditions?
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The reaction will proceed fast with the formation of the explosive products.
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The reaction will not occur spontaneously.
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The reaction will never reach equilibrium.
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The reaction will proceed spontaneously from left to right.
Pregunta 25
Pregunta
THE ENZYME-SUBSTRATE COMPLEX:
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Is a key concept that helps to explain how enzymes reduce activation energy for chemical reactions.
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Is a key concept that helps to explain how enzymes can reduce the Gibb’s free energy for a chemical reaction.
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Is a key concept that helps to explain how enzymes can exhibit diverse substrate specificity.
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Is a key concept that helps to explain how enzymes may exhibit Michaelis-Menton kinetics.
Pregunta 26
Pregunta
THE ENTHALPY CHANGE ASSOCIATED WITH A BIOCHEMICAL REACTION:
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Is a term used to describe the amount of randomness or disorder that results as the reaction proceeds
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Is a term used to describe the amount of ‘free energy’ change that results as the reaction proceeds
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Is a term used to describe the amount of heat that is produced or consumed as the reaction proceeds
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Is always determined at room temperature (25oC)
Pregunta 27
Pregunta
ENZYMES USUALLY UTILISE ONE OR MORE TRANSITION METAL ATOMS AT THE ACTIVE SITE TO:
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Facilitate substrate binding
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Facilitate transition state formation
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Facilitate stabilisation of the tertiary structure
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Facilitate conformational changes in the protein during the catalytic cycle
Pregunta 28
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ENZYMES:
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Reduce the entropy associated with chemical reactions
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Reduce the enthalpy associated with chemical reactions
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Reduce the Gibb’s free energy associated with chemical reactions
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Reduce the activation energy associated with chemical reactions
Pregunta 29
Pregunta
CONSIDER TWO REACTIONS. REACTION 1 HAS A ΔG°′ VALUE OF -20 kJ.mol-1 AND REACTION 2 HAS A ΔG°′ VALUE OF -50 kJ.mol-1. WHICH REACTION PROCEEDS AT THE FASTEST RATE AT ROOM TEMPERATURE AND PRESSURE AND pH 7?
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Reaction 1
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Reaction 2
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They both occur at much the same rate
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It is not possible to know this from the data provided
Pregunta 30
Pregunta
THE CATALYTIC EFFICIENCY OF AN ENZYME CATALYSED REACTION:
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Can be described by the ratio: kCAT/KM
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Can be described by the ratio: KM/kCAT
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Can be described by the ratio: Vmax/kCAT
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Can be described by the ratio: kCAT/Vmax
Pregunta 31
Pregunta
WHEN CONSIDERING ENZYME CATALYTIC MECHANISMS, ACID-BASE CATALYSIS IS USUALLY DEPENDANT UPON:
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Hydrogen bonding with at least one amino acid side chain at the active site to facilitate formation of the transition state.
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Hydrogen bonding between the carbonyl and amide groups of peptide bonds to facilitate formation of the transition state.
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Hydrogen bonding between a water molecule and the substrate to facilitate formation of the transition state.
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Hydrogen bonding with an oxidised metal ion prosthetic group in the active site to facilitate formation of the transition state.
Pregunta 32
Pregunta
IF THE ΔG°' OF THE REACTION A → B is –20 kJ/mol, WHAT WILL HAPPEN IN THE PRESENCE OF A SPECIFIC ENZYME UNDER STANDARD CONDITIONS?
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The reaction will stop
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The reaction will proceed spontaneously from B to A
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The reaction will proceed spontaneously from A to B
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The reaction will not occur spontaneously
Pregunta 33
Pregunta
FOR THE FOLLOWING REACTION:
L-Malate + NAD+ → Oxaloacetate + NADH + H+ ΔG°' = +29.7 kJ/mol.
WHICH OF THE FOLLOWING STATEMENTS IS CORRECT?
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This reaction can only occur in a cell in which NADH is converted to NAD+ by the respiratory chain
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This reaction can only occur in a cell if it is coupled to another reaction for which ΔG°' is large and negative
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This reaction may occur in cells at some concentrations of substrate and product
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This reaction is energy-releasing
Pregunta 34
Pregunta
IN MICHAELIS-MENTON KINETICS, FORMATION OF THE ENZYME-SUBSTRATE COMPLEX:
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Is always the rate limiting step in an enzyme catalysed reaction
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Is never the rate limiting step in an enzyme catalysed reaction
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Is always a necessary pre-requisite to formation of the transition state and therefore product turnover
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Is never a necessary pre-requisite to formation of the transition state and therefore product turnover
Pregunta 35
Pregunta
COMPETITIVE INHIBITORS:
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alter the Vmax of the reaction
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show irreversible binding to their target enzyme
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resemble the structure of the natural substrate/product molecule
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bind at a site distant from the active site
Pregunta 36
Pregunta
MULTIPLICATION OF UBIQUITIN TAGGING:
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Inhibits proteosome-mediated protein degradation
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Is essential for proteosome-mediated protein degradation
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Enhances proteosome-mediated protein degradation
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Has nothing to do with proteosome-mediated protein degradation
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