Chap 7- Kinetics And Regulation

Question 1

Allosteric enzymes def

Answer 1

Prevents chaos and allows for the efficient integration of metabolism. They are not only catalysts but also information sensors. They sense signals in the environment that allow them to adjust the rates of their reactions to meet the metabolic needs of the cell and facilitate the efficient coordination of the various metabolic pathways.

Question 2

Kinetics and enzyme kinetics def

Answer 2

Kinetics is the study of the rates of chemical reactions and enzyme kinetics is the study of rates if enzyme-catalyzed reactions.

Question 3

What is the velocity of the reaction, how is it measured?

Answer 3

The velocity of the reaction, V, is the amount of reactant that disappears in a specified unit if time. Equal to the velocity of the appearance of the product or the amount of product that appears in a specified unfit of time. The velocity of the reaction is directly related to the concentration of reactant by the rate constant k.
V=k[A]

Question 4

What is a first order reaction and what are the units of the rate constant?

Answer 4

Reactions in which the velocity is directly proportional to the reactant concentration are first order. The rate constant has units of 1/s.

Question 5

What is a second order reaction and what are the units of the rate constant?

Answer 5

A second order reaction has two reactants, bimolecular. Units of 1/Ms

Question 6

What is a pseudo-first order reaction?

Answer 6

If the concentration of one reactant greatly exceeds the other, which is present at low concentrations, the reaction rate will be first order with respect to the lower concentration and won’t depend on the higher concentration.

Question 7

How can a reaction be zero order?

Answer 7

When the rate is independent of reactant concentration. Enzyme-catalyze reactions can approximate zero order reactions in some cases.

Question 8

What did Michaelis and Menten discover?

Answer 8

An enzyme needed to bind substrate before catalysis could take place. The ES complex is a necessary intermediate in catalysis.

Question 9

What does the Michaelis Menten equation describe?

Answer 9

It describes the variation of enzyme activity as a function of substrate concentration.

Question 10

What is the Michaelis constant?

Answer 10

It is a compilation of rate constants that is unique to each enzyme and is independent of enzyme concentration. Describes the properties of the enzyme-substrate interaction and will vary for enzymes that can use different substrates.

Question 11

How is maximum velocity reached?

Answer 11

Vmax is attained only when all of the enzyme, Et, is bound to substrate.
Vmax is directly dependent if enzyme concentration.

Question 12

What does it mean to say an enzyme is saturated?

Answer 12

All of the available enzyme is bound to substrate and the addition of substrate will not affect the velocity. Enzyme is displaying zero order kinetics. The enzyme is operating at Vmax.

Question 13

What is kM equal to?

Answer 13

It is equal to the substrate concentration at which the reaction velocity is half its maximal value.

Question 14

What does the Km value of an enzyme depend on?

Answer 14

Depends on the particular substrate and on environmental conditions such as pH, temperature, and ionic strength.
Km is equal to the concentration of substrate at which half of the active sites are filled.

Question 15

What does K provide a measure of?

Answer 15

Km provides a measure of the substrate concentration required for significant catalysis to take place.

Question 16

What is the turnover number of an enzyme?

Answer 16

The number of substrate molecules that an enzyme can convert into product per unit time when the enzyme is fully saturated with substrate. The turnover number is equal to the rate constant, k2.

Question 17

What happens when substrate concentration is much lower than the value of Km?

Answer 17

All of the active sites are empty, the concentration of free enzymes is near,y equal to the total concentration of enzyme. The enzymatic velocity depends on the values of kcat/km, [S], and [E]t.
Kcat/km is the rate constant, called the specificity constant, for the interaction of S and E. the rate constant takes into account the rate of catalysis with a particular substrate, kcat, and the nature of the enzyme-substrate interaction, km.

Question 18

What does it mean for an enzyme to attain kinetic perfection?

Answer 18

Their catalytic velocity is restricted only by the rate at which they encounter substrate in the solution.

Question 19

What are the two classes of multiple substrate reactions?

Answer 19

Sequential reactions and double displacement reactions.

Question 20

Sequential reactions def

Answer 20

All substrates must bind to the enzyme before any product is released. A ternary complex consisting of the enzyme and both substrate forms. They can be either ordered, in which the substrates bind the enzyme in a defined sequence, and random.

Question 21

Double displacement reactions def

Answer 21

One or more products are released before all substrates bind the enzyme. Contains a substituted enzyme intermediate, in which the enzyme is temporarily modified. The substrates and products appear to bounce on and off the enzyme

Question 22

Allosteric enzymes def

Answer 22

Enzymes that regulate the flux of biochemicals through metabolic pathways. Key features of Allosteric enzymes include the regulation of catalytic activity by environmental signals, kinetics that are more complex than those of MM enzymes, and quaternary structure with multiple active sites in each enzyme.

Question 23

How can the production of product F be regulated to meet cellular requirement without making more than needed?

Answer 23

When sufficient F is present, F can bind reversibly to e1, the enzyme catalyzing the committed step, and inhibit the reaction.

Question 24

Feedback inhibition def

Answer 24

When the final product binds to the enzyme catalyzing the committed step and inhibits the reaction. Feedback inhibition is a common means of biochemical regukation

Question 25

How do feedback inhibitors work?

Answer 25

They usually bear no resemblance to the substrate or the product of the enzyme they inhibit. They do not bind at the active site but at a distinct regulatory site on the Allosteric enzymes include

Question 26

How are Allosteric enzymes regulated?

Answer 26

They are regulated by molecules that bind to sites other than the active sites. They always catalyze the committed step of metabolic pathways.

Question 27

How does the velocity vs substrate conc curve differ for an MM enzyme and an Allosteric enzymes?

Answer 27

Allosteric enzymes display a sigmoidal dependence of reaction velocity on substrate concentration in contrast to the hyperbolic

Question 28

What two properties are unique to Allosteric enzymes?

Answer 28

1) regulation of catalytic activity 2) sigmoidal kinetics

Question 29

Concerted model, what it’s based on

Answer 29

1) Allosteric enzymes have multiple active sites on different polypeptide chains. 2) the enzyme can only exist in two distinct conformations or states, one state designated R for relaxed, is the active conformation, which catalyzes reactions. The other state, T for tense, is less active. In the absence of substrate or signal molecules 3) the converted model also requires that all of the subunits or active sites of the enzyme must be I;the same state, all must be T or all must be R. This requirement is called the symmetry rule. 4) substrate S binds more readily to the R form of the enzyme that to the T form.

Question 30

Threshold effect def

Answer 30

The activity of Allosteric enzymes is more sensitive to changes in substrate concentration near km than are MM enzymes with the same Vmax. Below a certain substrate concentration, there is little enzyme activity however after the threshold has been reached, enzyme activity increases rapidly.

Question 31

What does cooperativity ensure?

Answer 31

It ensures that most of the enzyme is either on, R state, or off, T state.

Question 32

What do regulatory molecules do? Positive and negative regulators?

Answer 32

The regulatory molecules after the equilibrium between T and R forms. A positive effector binds to the R form at a regulatory site, distinct from the active site, and stabilizes this form, increasing the concentration of R and making an R and S interaction more likely. A negative effector binds to T and stabilizes it, a negative effector increases the concentration of T and decreases the likelihood of an R binding to an S.

Question 33

How do positive and negative effectors affect the threshold concentration of needed for activity?

Answer 33

The positive effector lowers the threshold concentration and the negative effector raises the threshold concentration.

Question 34

Heterotropic effects def

Answer 34

The effects of regulatory molecules on Allosteric enzymes. Shift the sigmoidal curve to the left, activators, or the right, inhibitors.

Question 35

Homotropic effects def

Answer 35

The effects of substrates on Allosteric enzymes. Account for the sigmoidal nature of kinetics curve.

Question 36

Molecular heterogeneity def

Answer 36

The ability of a molecule, with the passage of time, to assume several different structures that differ slightly in stability.

Question 37

What is the difference between a first order rate constant and a second order rate constant?

Answer 37

First order has only one reactant. Units of the rate constant are 1/s. Second order depends on two reactants and has units of 1/Ms.

Question 38

What is the biological advantage of having a Km approximately equal to the substrate concentration normally available to an enzyme?

Answer 38

At substrate concentrations near the km, the enzyme displays significant catalysis yet is sensitive to changes in substrate concentration

Question 39

What is the defining characteristic for an enzyme catalyzing a sequential reaction or a double displacement reaction?

Answer 39

Sequential reactions are characterized by the formation of a ternary complex consisting of the enzyme and both substrates. Double-displacement reactions always require the formation of a temporarily substituted enzyme intermediate.