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Enzymes/N-metabolism Years 2013-2009

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Quiz on Enzymes/N-metabolism Years 2013-2009, created by MatthewEllis96 on 03/02/2015.
MatthewEllis96
Quiz by MatthewEllis96, updated more than 1 year ago
MatthewEllis96
Created by MatthewEllis96 over 9 years ago
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Resource summary

Question 1

Question
The Michaelis-Menton model:
Answer
  • Is based on the assumption that a transition state is formed in the enzyme active site.
  • Is based on the assumption that an enzyme catalysed reaction is mediated at the active site of an enzyme.
  • Is based on the assumption that a biochemical reaction is at equilibrium.
  • Is based on the assumption that a biochemical reaction occurs at a steady state.

Question 2

Question
The Michaelis-Menton constant, Km:
Answer
  • Is associated with the maximum enzyme activity observed when the all active sites in an enzyme are saturated with substrate.
  • Is associated with the number of substrate molecules reacted on by an enzyme molecule per unit time.
  • Is associated with the affinity of an enzyme for a specific substrate.
  • Is associated with the selectivity of an enzyme for different substrates.

Question 3

Question
In enzyme kinetics, the ratio of constants kcat/Km:
Answer
  • Is a measure of the rate of acceleration carried out by the enzyme.
  • For a given enzyme is independent of the substrate used.
  • Has units of concentration.
  • Gives an idea of the enzymes catalytic efficiency.

Question 4

Question
The Km/Kcat ratio:
Answer
  • Is associated with the maximum enzyme activity observed when the all active sites in an enzyme are saturated with substrate.
  • Is associated with the number of substrate molecules reacted on by an enzyme molecule per unit time.
  • Is associated with the affinity of an enzyme for a specific substrate.
  • Is associated with the selectivity of an enzyme for different substrates.

Question 5

Question
In enzyme catalysis, the term ‘approximation’ refers to:
Answer
  • A catalytic strategy facilitating transition state formation through covalent bond formation between the substrate and enzyme active site.
  • A catalytic strategy facilitating transition state formation through hydrogen bond formation and electrostatic bond formation between the substrate and enzyme active site.
  • A catalytic strategy facilitating transition state formation through interaction involving metal ions and substrate in the enzyme active site.
  • A catalytic strategy facilitating transition state formation through direct transfer of a proton to or from the substrate in the enzyme active site.

Question 6

Question
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:
Answer
  • Half of Vmax
  • Two thirds of Vmax
  • Double Vmax
  • Three times Vmax

Question 7

Question
Koshland’s induced fit model for enzyme-substrate complex formation:
Answer
  • May explain why enzymes have particular substrate specificity.
  • May explain why enzymes are able to catalyse chemical reactions that cannot be facilitated in any other way
  • May explain why enzymes increase the rate of a reaction by reduction of the activation energy change for the reaction
  • May explain why enzymes can effectively reduce the loss of energy from a chemical reaction as heat

Question 8

Question
Enzymes:
Answer
  • are chemically altered at the end of their reaction
  • are involved in changing the equilibrium constant of the reaction that they catalyse
  • bind their substrates at their active site(s)
  • increase the activation energy of the reaction they catalyse

Question 9

Question
The Michaelis constant, Km:
Answer
  • Is a measure of the rate acceleration caused by the enzyme
  • For a given enzyme is independent of the substrate used
  • Has units of concentration
  • Gives an idea of the enzyme’s catalytic efficiency

Question 10

Question
The Vmax of an enzyme catalysed reaction:
Answer
  • Is altered when a competitive inhibitor is present
  • Can be determined from the intercept on the x-axis of a Lineweaver-Burk plot
  • Is the maximum rate at which the enzyme can convert substrate into product
  • Has units of concentration

Question 11

Question
Proteosome-mediated proteolysis:
Answer
  • Is controlled by serine protease enzymes.
  • Is a key part of the control mechanism in the eukaryote cell cycle
  • Is a key part of the control mechanism in the prokaryote cell cycle
  • Is controlled by ubiquinone activating enzymes.

Question 12

Question
The Alanine Cycle:
Answer
  • Is completely located in the mitochondrial matrix.
  • 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.
  • 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.
  • Is located in the cell membrane of muscle cells.

Question 13

Question
The transition state for an enzyme-catalysed reaction:
Answer
  • Describes the way the substrate interacts with the enzyme.
  • Descibes the protein tertiary structure when the enzyme substrate is converted to a product.
  • Describes the form the substrate takes that facilitates the formation of a low energy intermediate during the catalytic cycle.
  • Describes an intermediate in the catalytic cycle that is produced in order to minimise the activation energy for the reaction.

Question 14

Question
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:
Answer
  • 15 mM
  • 30 mM
  • 45 mM
  • 60 mM

Question 15

Question
The value of ΔG0’ for an enzyme catalysed reaction:
Answer
  • Will always be negative if an enzyme catalysed reaction proceeds spontaneously.
  • Will always be positive if an enzyme catalysed reaction proceeds spontaneously.
  • Will always be equal to the ΔG value for a reaction where both the reactants and products have an equal concentration.
  • Will only apply to a reaction occurring if the pH = 7.0 in aqueous solution.

Question 16

Question
An abzyme is:
Answer
  • An enzyme that is protein-engineered to work like an antibody.
  • An antibody that is protein-engineered to work like an enzyme.
  • An enzyme that has high affinity for a transition state analogue.
  • An antibody that has high affinity for a transition state analogue.

Question 17

Question
An oxyanion hole is:
Answer
  • 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.
  • 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.
  • A region of the active site that facilitates binding of positively charged oxygen- containing groups present in a substrate.
  • A region of the active site that facilitates binding of negatively charged oxygen-containing groups present in a substrate.

Question 18

Question
Which of the following catalytic strategies is not employed by the enzyme chymotrypsin:
Answer
  • Approximation.
  • Acid-base catalysis.
  • Metal-ion catalysis.
  • Covalent catalysis.

Question 19

Question
The urea cycle:
Answer
  • Is completely located in the mitochondrial matrix – preventing the exposure of free ammonium to other components of the eukaryote cell.
  • 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.
  • 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.
  • Is completely located in the cytoplasm of the cell – preventing the exposure of free ammonium to other components of the eukaryote cell.

Question 20

Question
An end-product can act to inhibit an enzyme by binding at the:
Answer
  • Active site
  • Activation site
  • Allosteric site
  • Transitional site

Question 21

Question
Serine proteases:
Answer
  • Are proteases that hydrolyse polypeptides with serine in the F1 position
  • Are proteases that are found in the cytoplasm of all cells
  • Utilise a serine residue at the active site to facilitate substrate binding
  • Utilise a serine residue at the active site to facilitate cleavage of peptide bonds

Question 22

Question
In acid-base catalysis:
Answer
  • An acidic- or basic- amino acid in the active site of an enzyme facilitates transition state formation by hydrogen abstraction from an appropriate substrate.
  • 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.
  • Both are correct.
  • Neither are correct.

Question 23

Question
The protein ubiquitin:
Answer
  • Can be covalently linked to proteins via the N-terminus glycine residue.
  • Is a polypeptide.
  • Is an essential component of eukaryote respiratory chains.
  • Can be covalently linked to proteins via isopeptide bond formation.

Question 24

Question
If the ΔG°′ of the reaction Malate → Oxaloacetate is +30 kJ/mol, what will happen in the presence of malate dehydrogenase under standard conditions?
Answer
  • The reaction will proceed fast with the formation of the explosive products.
  • The reaction will not occur spontaneously.
  • The reaction will never reach equilibrium.
  • The reaction will proceed spontaneously from left to right.

Question 25

Question
THE ENZYME-SUBSTRATE COMPLEX:
Answer
  • Is a key concept that helps to explain how enzymes reduce activation energy for chemical reactions.
  • Is a key concept that helps to explain how enzymes can reduce the Gibb’s free energy for a chemical reaction.
  • Is a key concept that helps to explain how enzymes can exhibit diverse substrate specificity.
  • Is a key concept that helps to explain how enzymes may exhibit Michaelis-Menton kinetics.

Question 26

Question
THE ENTHALPY CHANGE ASSOCIATED WITH A BIOCHEMICAL REACTION:
Answer
  • Is a term used to describe the amount of randomness or disorder that results as the reaction proceeds
  • Is a term used to describe the amount of ‘free energy’ change that results as the reaction proceeds
  • Is a term used to describe the amount of heat that is produced or consumed as the reaction proceeds
  • Is always determined at room temperature (25oC)

Question 27

Question
ENZYMES USUALLY UTILISE ONE OR MORE TRANSITION METAL ATOMS AT THE ACTIVE SITE TO:
Answer
  • Facilitate substrate binding
  • Facilitate transition state formation
  • Facilitate stabilisation of the tertiary structure
  • Facilitate conformational changes in the protein during the catalytic cycle

Question 28

Question
ENZYMES:
Answer
  • Reduce the entropy associated with chemical reactions
  • Reduce the enthalpy associated with chemical reactions
  • Reduce the Gibb’s free energy associated with chemical reactions
  • Reduce the activation energy associated with chemical reactions

Question 29

Question
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?
Answer
  • Reaction 1
  • Reaction 2
  • They both occur at much the same rate
  • It is not possible to know this from the data provided

Question 30

Question
THE CATALYTIC EFFICIENCY OF AN ENZYME CATALYSED REACTION:
Answer
  • Can be described by the ratio: kCAT/KM
  • Can be described by the ratio: KM/kCAT
  • Can be described by the ratio: Vmax/kCAT
  • Can be described by the ratio: kCAT/Vmax

Question 31

Question
WHEN CONSIDERING ENZYME CATALYTIC MECHANISMS, ACID-BASE CATALYSIS IS USUALLY DEPENDANT UPON:
Answer
  • Hydrogen bonding with at least one amino acid side chain at the active site to facilitate formation of the transition state.
  • Hydrogen bonding between the carbonyl and amide groups of peptide bonds to facilitate formation of the transition state.
  • Hydrogen bonding between a water molecule and the substrate to facilitate formation of the transition state.
  • Hydrogen bonding with an oxidised metal ion prosthetic group in the active site to facilitate formation of the transition state.

Question 32

Question
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?
Answer
  • The reaction will stop
  • The reaction will proceed spontaneously from B to A
  • The reaction will proceed spontaneously from A to B
  • The reaction will not occur spontaneously

Question 33

Question
FOR THE FOLLOWING REACTION: L-Malate + NAD+ → Oxaloacetate + NADH + H+ ΔG°' = +29.7 kJ/mol. WHICH OF THE FOLLOWING STATEMENTS IS CORRECT?
Answer
  • This reaction can only occur in a cell in which NADH is converted to NAD+ by the respiratory chain
  • This reaction can only occur in a cell if it is coupled to another reaction for which ΔG°' is large and negative
  • This reaction may occur in cells at some concentrations of substrate and product
  • This reaction is energy-releasing

Question 34

Question
IN MICHAELIS-MENTON KINETICS, FORMATION OF THE ENZYME-SUBSTRATE COMPLEX:
Answer
  • Is always the rate limiting step in an enzyme catalysed reaction
  • Is never the rate limiting step in an enzyme catalysed reaction
  • Is always a necessary pre-requisite to formation of the transition state and therefore product turnover
  • Is never a necessary pre-requisite to formation of the transition state and therefore product turnover

Question 35

Question
COMPETITIVE INHIBITORS:
Answer
  • alter the Vmax of the reaction
  • show irreversible binding to their target enzyme
  • resemble the structure of the natural substrate/product molecule
  • bind at a site distant from the active site

Question 36

Question
MULTIPLICATION OF UBIQUITIN TAGGING:
Answer
  • Inhibits proteosome-mediated protein degradation
  • Is essential for proteosome-mediated protein degradation
  • Enhances proteosome-mediated protein degradation
  • Has nothing to do with proteosome-mediated protein degradation
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