BioChemistry Ch 8

The graph presents three activation energy profiles for a chemical reaction (the hydrolysis of sucrose): an uncatalyzed reaction, and the same reaction catalyzed by two different enzymes. Rank these by reaction rate, as measured by the rate of product formation (from the most product formed to the least product formed). To rank items as equivalent, overlap them.

(Highest to lowest) reaction catalyzed by enyme B > reaction catalyzed by enzyme A > catalyzed reaction

The enzyme urease catalyzes the hydrolysis of urea to ammonia plus carbon dioxide. At 21 ∘C∘C the uncatalyzed reaction has an activation energy of about 125 kJ/mol, whereas in the presence of urease the activation energy is lowered to about 46 kJ/mol. By what factor does urease increase the velocity of the reaction?

1.1x10^14

Estimate Vmax from a direct graph of v versus [S] using the plot you created in part A.

150

Use the equation from part E to estimate Vmax.

164

Match each term with its definition.

1:B; 2:C; 3:A

Match each of the following terms from the Michaelis-Menten equation to its correct definition.

1:B; 2:D; 3:C; 4:A

Match each function with the name of a major enzyme class.

1:B; 2:E; 3:A; 4:F

Please match each cofactor with its function.

1:C; 2:D; 3:A; 4:B

Determine the apparent KM at each inhibitor concentration.

2.48,3.88,5.15mmol/L

Assuming that the TT155 side chain cannot H-bond to the oxyanion intermediate, by how much (in kJ/mol) does N155 appear to stabilize the transition state at 37∘C?

20 kJ/mol

Estimate KM from a direct graph of v versus [S] using the plot you created in part A.

25

Use the equation from part E to estimate KM.

32

The rate constant for a certain reaction is k = 8.60×10^−3 s−1 . If the initial reactant concentration was 0.950 MM, what will the concentration be after 15.0 minutes?

4.13x10^-4 M

Estimate KIKI from these data.

4.98mM

Determine the apparent Vmax at each inhibitor concentration.

5.13,5.13,5.11(mmol/L)min−1

Arrange the events for the hydrolysis of amide bonds by chymotrypsin in their correct order.

6, 1, 3, 5, 4, 2

A zero-order reaction has a constant rate of 4.30×10−4 M/s. If after 55.0 seconds the concentration has dropped to 5.00×10−2 M, what was the initial concentration?

7.37x10^-2 M

Which of the following statements about inhibitors of enzyme-catalyzed reactions is TRUE?

A competitive inhibitor does not affect Vmax.

Consider the enzyme-catalyzed reaction with Vmax=164 (μmol/L)min−1 and KM=32 μmol/L. A.)If the total enzyme concentration was 1 nmol/L, how many molecules of substrate can a molecule of enzyme process in each minute? B.)Calculate kcat/KM for the enzyme reaction.

A.) 164000 B.) 85x10^6

A.) Calculate kcat for the reaction. B.) Calculate KM for the enzyme. C.) When the reactions in part (B) are repeated in the presence of 12 μM of an uncompetitive inhibitor, the y-intercept of the Lineweaver-Burk plot is 0.352 (μmol−1μml s). Calculate KI′ for this inhibitor.

A.) 7.82×104s−1 B.) 124μM C.) 1.45×10−7 M

A.) R15S B.) C1S C.) T147S

A.) Activation of the molecule will be greatly reduced due to removal of the RR that is binded in its active site. B.) If activation occurs, the NN-terminal peptide will no longer be constrained by an SSS-S bond and may be released. C.) Automodification of ππ-chymotrypsin to αα-chymotrypsin could be reduced, the effect on activation might be slight.

A.) Explain this observation.

A.) At [S] > KM the effect of the inhibitor on reducing Vmax is apparent because as [S] increases, V approaches Vmax/α′.

A.) Enalapril is administered in pill form, but enalaprilat must be administered intravenously. Why do you suppose enalapril works as a pill, but enalaprilat does not? B.) Enalaprilat is a competitive inhibitor of the angiotensin-converting enzyme (ACE), which cleaves the blood-pressure regulating peptide angiotensin I. ACE has a KM = 12 μM for angiotensin I, which is present in plasma at a concentration of 75 μMμM. When enalaprilat is present at 2.4 nM, the activity of ACE in plasma is 10%% of its uninhibited activity. What is the value of KI for enalaprilat?

A.) Enalaprilat is too polar to cross membranes, whereas enalapril can cross membranes to get from the gut to circulation. B.) 3.7×10^−11 M

A.) An enzyme contains an active site aspartic acid with a pKapKa = 5.0, which acts as a general acid catalyst. Choose the curve of enzyme activity (reaction rate) versus pHpH for the enzyme (assume the protein is stably folded between pHpH 2-12 and that the active site Asp is the only ionizable residue involved in catalysis). B.) Briefly explain the shape of your curve.

A.) Picture B.) The Asp must be protonated to act as a general acid catalyst; thus, activity will be higher when pH < pKa and lower when pH > pKa.

Problem 8.1 A.)Choose the equation for a first-order reaction. B.) When t=t1/2, what is the value of −kt1/2? C.) What is the expression for the half-life for a first-order reaction? D.) Based on the half-life expression for a first-order reaction, determine its constant of proportionality?"

A.) ln[A]t/[A]0=−kt B.) -0.693 C.) t1/2=0.693/k D.) 0.693

A.) Indicate what type of inhibition is predicted based on Lineweaver-Burk plot. B.) Indicate which line corresponds to the reaction without inhibitor and which line corresponds to the reaction with inhibitor present. C.)Indicate what type of inhibition is predicted based on Lineweaver-Burk plot. D.) Indicate which line corresponds to the reaction without inhibitor and which line corresponds to the reaction with inhibitor present. E.) Indicate what type of inhibition is predicted based on Lineweaver-Burk plot. F.) Indicate which line corresponds to the reaction without inhibitor and which line corresponds to the reaction with inhibitor present.

A.) mixed inhibition B.) blue- without inhibitor, red- with inhibitor C.) competitive inhibition D.) blue-without inhibitor, red-with inhibitor E.) uncompetitive inhibition F.) blue-without inhibitor, red-with inhibitor

A.) In general, enzymes are what kinds of molecules? B.) Enzymes work by _____. C.) An enzyme _____. D.)What name is given to the reactants in an enzymatically catalyzed reaction? E.) As a result of its involvement in a reaction, an enzyme _____. F.) What is the correct label for "A"

A.) proteins B.)reducing Ea C.) is an organic catalyst D.) substrate E.) is unchanged F.) energy of activation

A.) In which region does the reaction rate remain constant? B.) In which region is the enzyme saturated with substrate? C.) Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction?

A.) region C B.) region C C.) increase enzyme concentration

A.) In which region does the reaction rate remain constant? B.)In which region is the enzyme saturated with substrate? C.)Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction?

A.) region C B.) region C C.) increase the enzyme concentration

A.) The Haber process is typically carried out at a temperature of approximately 500∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C? B.) What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased? C.) Which of the following would increase the rate of the reverse reaction? D.) What will happen to the rates of the forward and reverse reactions when a catalyst is added?

A.) the reaction rate would decrease B.) the reaction rate would decrease C.) increasing the concentration of ammonia D.)Both forward and reverse rates increase

Which of the following is a feature of allosteric regulation of enzyme activity?

All of the above

Which of the following describes a mechanism that enzymes use to achieve their rate enhancement of reactions?

All of the listed choices describe mechanisms used by enzymes to achieve their rate enhancement of reactions.

Which of the following statement is FALSE?

At a given temperature and time all molecules in a solution or a sample will have the same energy.

B.) Determine Vmax in the absence of inhibitor. C.) Determine Vmax in the presence of inhibitor. D.) Determine KM in the absence of inhibitor. E.) Determine KM in the presence of inhibitor.

B.) 5.13 C.) 2.97 D.) 2.48 E.) 2.55

B.) You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. C.) You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down.

B.) The enzymes is inactive at this point. New enzyme must be added to regain enzyme activity C.) Add more substrate; it will outcompete the inhibitor and increase the reaction rate

Which of the following statements about the various methods of enzyme inhibition is NOT true?

Competitive inhibitors bind at a different site than substrate, altering the ability of the enzyme to bind its native target.

Which of the following statements are true with respect to enzyme activity?

Enzymes speed up the reaction rate Enzymes are regenerated when the reaction is completed Enzymes affect the reaction pathway by forming an enzyme-substrate complex

A mutation causing an amino acid change in an enzyme that affects the turnover number kcat will always affect the KM as well.

False

A stopped-flow apparatus is used to measure rates of pre-steady state slow enzymatic reactions.

False

Catalysts affect the thermodynamic favorability of a chemical reaction.

False

Electrostatic catalysis proceeds via covalent bonding interactions.

False

Non-catalyzed biochemical reactions always occur at physiological useful timescales.

False

Which of the following amino acid residues are often involved in proton transfers in enzyme-catalyzed reactions?

Histidine, aspartate, glutamate, arginine, and lysine

Which of the following statements BEST describes the Michaelis-Menton constant KM?

It is numerically equal to the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction.

Which of the following is NOT a feature of substrate-level enzyme regulation?

It is sufficient for regulation of most enzyme-catalyzed reactions.

In a favorable reaction the free energy of the products is ________ than the free energy of the reactants.

Less

Given the two plots in parts A and D and the analysis methods available within each part, which is better to estimate Vmax and KM?

Lineweaver-Burk plot

Which myoglobin is more thermodynamically stable, the mutant or the wild-type?

Mutant myoglobin

Considering both of the mechanisms proposed for catalysis by lysozyme, which of the following rate-enhancing features does lysozyme use to increase the rate of the hydrolysis reaction it catalyzes?

Only choices 1, 2, and 4 are correct.

Consider the following reaction:A → BWhich of the following statements about this reaction are correct?

Only statements 1 and 2 are correct.

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?

P4 binds E1 and deactivates it

Subtilisin is used in some laundry detergents to help remove protein-type stains. What unusual kind of stability does this suggest for subtilisin?

The enzyme must be stable both to the presence of detergents and to moderately high temperatures.

Which of the following statements about the oxyanion hole is NOT true?

This preformed loop is properly positioned to stabilize the negatively charged tetrahedral intermediate involved in amide bond hydrolysis.

Covalent modification can either activate or inhibit enzymes.

True

Metal ions are often required for catalytic efficiency but they may not remain permanently bound to the protein or take part in the catalytic process.

True

Pyruvate carboxylase is an example of the ligase class of enzymes.

True

Enzymes can accelerate reactions by:

all of the above. Submit

The cofactor NAD+ is:

an oxidant

What kind of inhibitor is inhibitor B?

competitive

Elastase is closely related to chymotrypsin. Suggest two kinds of amino acid residues you might expect to find in or near the active site.

histidine serine

Subtilisin does have a problem in that it becomes inactivated by oxidation of a methionine close to the active site. Suggest a way to make a better subtilisin.

hydrophobic; hydrophobic; Val

A second-order reaction:

is characterized by two molecules coming together to form a product.

The value you calculated in part D represents the strength of the H-bond between N155 and the oxyanion in the transition state. This value is higher than typical H-bonds in water. How might this observation be rationalized? Hint: Coulomb's Law.

lower; stronger

What kind of inhibition (competitive, uncompetitive, or mixed) is involved?

mixed

The equilibrium constant for a first-order ________ reaction is equivalent to the ratio of the rate constant for the forward and reverse reactions.

reversible

The lock and key model of substrate binding and enzymatic catalysis explains:

substrate specificity.

Choose the equation of the line.

y=0.196x+0.0061

Is this a fairly efficient enzyme? (See table below)

yes, this is a very efficient enzyme