Ch 6 Enzymes: The Catalysts of Life

how specific is the enzyme? what this implies within the body?

-Because of the specific fit between enzyme and substrate, each enzyme can catalyze only one kind of reaction involving specific substrates. -Thousands of different enzymes may be required to carry out all of a cell's metabolic processes.

what is an example of competitive inhibitors?

-Most medications are enzyme inhibitors of one kind or another. -drugs like antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction)

what are the two types of reversible enzyme inhibitors?

-competitive -non-competitive

In a graph of reaction rate vs substrate concentration, In which region is the enzyme saturated with substrate?

-in the region where there is a high substrate concentration and the hyperobola begins to be a horizonal line

what are the 2 classifications of enzyme inhibitors?

-irreversible -reversible

An enzyme _____. is a source of energy for endergonic reactions can bind to nearly any molecule is an organic catalyst is a inorganic catalyst increases the EA of a reaction

-is an organic catalyst -Enzymes are proteins that behave as catalysts.

In a graph of reaction rate vs substrate concentration, at what point does the reaction rate remains constant?

-when saturation point happens, the point where there is a high substrate concentration -when the hyperbola is a horizontal line

How does a living cell overcome the energy barrier so that its metabolic reactions can occur quickly and precisely?

A special kind of protein called an enzyme is the answer.

exergonic reaction

A spontaneous chemical reaction, in which there is a net release of free energy.

Phosphoenolpyruvate (PEP) is considered an unstable molecule, whereas ATP is considered a metastable molecule. Which of the following is likely true about the nonenzymatic hydrolysis of PEP and the hydrolysis of ATP? The hydrolysis of ATP and PEP will occur spontaneously and quickly. The hydrolysis of ATP will be spontaneous and fast, whereas the hydrolysis of PEP will be nonspontaneous. The hydrolysis of ATP and PEP will be nonspontaneous. The hydrolysis of ATP and PEP will be spontaneous, but the hydrolysis of ATP will be much slower than the hydrolysis of PEP.

ATP and PEP will be spontaneous, but the hydrolysis of ATP will be much slower than the hydrolysis of PEP.

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. What can you do to speed the reaction up again? Add more inhibitor to speed up the reaction. Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Increase the temperature. Increase the pH.

Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

An enzyme serves as a _(role), _(doing what) without _(what happens to it during reaction). An enzyme does not _(what does not do to make a reaction to happen); instead, it _(what it does to make a reaction to happen)

An enzyme serves as a biological catalyst, increasing the rate of a reaction without being changed into a different molecule. An enzyme does not add energy to a reaction; instead, it speeds up a reaction by lowering the energy barrier.

what happens to enzymes as the substrate concentration increases?

As the concentration of substrate increases, the reaction rate increases, until the point where the active site is saturated with substrate.

what is the action of irreversible inhibitors and why?

Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive.

how can you decrease the effect of competitive inhibitors?

Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor.

what competitive inhibitors do?

Competitive inhibitors compete physically and structurally with the substrate for an enzyme's active site

Enzymes work by _____. increasing the potential energy difference between reactant and product decreasing the potential energy difference between reactant and product adding energy to a reaction reducing EA adding a phosphate group to a reactant

Enzymes work by reducing the energy of activation.

If exergonic reactions occur spontaneously, what keeps molecules from breaking apart and cell chemistry from racing out of control? (include what happens within the reaction to make it happen)

For any reaction to occur, even a downhill reaction, some energy must be added to get the reaction going. This energy is needed to break bonds in the reactant molecules. The energy needed to start a chemical reaction is called the energy of activation (EA). This required energy input represents a barrier that prevents even energy-releasing exergonic reactions from occurring without some added energy.

how many active sites are found in an enzyme? what happens here?

In general, an enzyme has one active site at which catalysis can occur. When the substrates are bound to the active site, the enzyme will catalyze the reaction.

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? Increase the pH. Increase the temperature. Increase the enzyme concentration. Increase the substrate concentration.

Increase the enzyme concentration.

what irreversible inhibitors do?

Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently

Why is the Lineweaver-Burk plot important in enzyme kinetics? It illustrates enzyme specificity. It makes it easier to determine Vmax. It is a single-reciprocal plot. It is nonlinear. It reveals the presence of prosthetic groups in enzymes.

It makes it easier to determine Vmax.

why an enzyme is so specific?

Its three-dimensional shape allows it to act only on specific molecules,

A competitive inhibitor will affect the ________ of an enzymatic reaction. S V max P K m K m and V max

K m

enzyme inhibitors.

Molecules other than substrates bind to enzymes. Some of these other molecules slow down the rate of the enzymatic reaction.

what noncompetitive inhibitors do?

Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme's shape

a hypothetical enzymatic pathway with four enzymes, labeled E1, E2, E3, and E4. The enzymes make products, labeled P0, P1, P2, P3, and P4. Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown? Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown? P0 binds E4 and activates it. P2 binds E2 and activates it. P4 binds E1 and deactivates it. P3 binds E2 and activates it P4 binds E3 and deactivates it.

P4 binds E1 and deactivates it.

what must be overcome in order for a reaction to proceed?

The energy of activation must be overcome in order for a reaction to proceed.

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? Removing the irreversible inhibitor should get the reaction working again. The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. Adding more substrate will increase the rate of reaction. Adding more inhibitor should get the reaction up to speed again.

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

Which of the following best describes a metastable state? This state is composed of the difference in activation energy of a catalyzed versus an uncatalyzed reaction. The metastable state is created by the prosthetic group of the enzyme. The metastable state is formed by transient complexes with the substrate. This state changes the position of the equilibrium but not the rate. The metastable state is a state of the substrate in which the reaction can proceed but typically requires a catalyst.

The metastable state is a state of the substrate in which the reaction can proceed but typically requires a catalyst.

An enzyme contains a catalytic histidine residue in its active site that must release an R group proton to solution in order to facilitate catalysis by the enzyme. Which of the following environmental conditions would be required for optimal enzyme activity? [explain] The pH of the environment should be relatively high. The pH of the environment should be relatively low. The pH of the environment would not matter. The environment should be set to the biochemical standard state.

The pH of the environment should be relatively high. reason: histidine (His) is a polar, charged amino acid (hydrophilic) and it one of the 3 basic amino acids

substrate

The reactant on which an enzyme works

active site

The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.

the methods that create the molecules within the body contain what?

These small molecules are often produced in enzymatic pathways that have three or more enzymes making modifications to the substrate.

A noncompetitive inhibitor will affect the ________ of an enzymatic reaction. S P K m V max K m and V max

V max

what happens to the rate of a reaction involving an enzyme when saturation is reached?

When the enzyme is saturated, the rate of the reaction will not increase with the concentration of substrates.

Which of the following is an example of a prosthetic group? a zinc ion a glycine residue a nickel catalyst a polypeptide chain carboxypeptidase A

a zinc ion

the competitive inhibitor competes with the substrate for the_on an enzyme

active site

The site on an enzyme that will bind the substrate is called the activation site. active site. catalyst. metastable site. prosthetic group.

active site.

Covalent modification affects the activity of an enzyme by adding or removing a chemical group. produces modifications that can sometimes be reversed. can involve the addition of phosphate groups. can activate an enzyme. all of the above

all of the above

An enzyme changes the position of the equilibrium of the reaction. is always a protein. does not change the rate at which the equilibrium is achieved. binds substrates in a manner that facilitates the formation of product. decreases the rate of a reaction.

binds substrates in a manner that facilitates the formation of product.

The Michaelis constant can be determined using the Lineweaver-Burk plot. is equal to twice the V max. is equal to the substrate concentration at V max/2. can be determined using the Lineweaver-Burk plot and is equal to the substrate concentration at V max/2. can be determined using the Lineweaver-Burk plot, is equal to twice the V ma, and is equal to the substrate concentration at V max/2.

can be determined using the Lineweaver-Burk plot and is equal to the substrate concentration at V max/2.

A competitive inhibitor binds to and inactivates the substrate. does not inhibit enzyme activity but does lower substrate concentration. irreversibly binds and inactivates the enzyme. cannot be processed by the enzyme. binds at a site other than the active site.

cannot be processed by the enzyme.

Which of the following is an enzyme? iron N-acetylmuramic acid carboxypeptidase A histidine ATP

carboxypeptidase A

A _inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate

competitive inhibitor

Substrate activation may involve (4)

donation of protons to the enzyme. a change in enzyme conformation induced by substrate binding. formation of temporary covalent bonds. accepting protons from the enzyme.

feedback inhibition is also known as_

end-product inhibition.

when the noncompetitive inhibitor is bonded to the enzyme, the shape of the _is distorted

enzyme

The phosphorylation of glucose to generate glucose-6-phosphate is catalyzed by the enzyme hexokinase. This enzyme, however, is allosterically inhibited by its own product, glucose-6-phosphate. This is an example of __________. covalent modification competitive inhibition feedback regulation irreversible inhibition

feedback regulation

when saturation is reached, the reaction rate is independent of what?

he reaction rate is independent of substrate concentration.

The induced-fit model involves a conformational change in the shape of the enzyme. was proposed by Hans Buchner. proposes that very strong covalent bonds are formed upon substrate binding. states that enzyme-substrate interactions are rigid. is also called the lock-and-key model.

involves a conformational change in the shape of the enzyme.

The active site for carboxypeptidase is formed by the interaction of two polypeptide chains. contains a glutamate residue at position 69. involves only 6 out of a total of 307 amino acids. contains amino acids that are contiguous to one another along the primary sequence of the protein. uses iron as the prosthetic group.

involves only 6 out of a total of 307 amino acids.

usually, an _inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity

irreversible

As a result of its involvement in a reaction, an enzyme _____. is used up loses energy loses a phosphate group permanently alters its shape. is unchanged

is unchanged

In a graph of energy vs reactants and products, what part of the parabola is found the energy of activation?

it is found between the reactant and the top or cuspid of the curve

a_inhibitor binds to a site on the enzyme that is not the active site

noncompetitive

Enzymes that catalyze the phosphorylation of other enzymes are __________. Enzymes that catalyze the phosphorylation of other enzymes are __________. ligases oxidoreductases protein kinases phosphoprotein phosphatases

protein kinases

In general, enzymes are what kinds of molecules? proteins minerals carbohydrates lipids nucleic acids

proteins

explain in general sense what the enzyme does to make a reaction to happen (include interaction with substrate and amount of energy needed)

s the substrates bind to the enzyme's active site, they are held in a position that facilitates the reaction. This takes less activation energy than the unaided reaction. Products form and are released. The enzyme emerges unchanged from the reaction.

Enzyme regulation may occur by several methods. Which of the following is not a means of enzyme regulation? saturation allosteric regulation substrate-level phosphorylation covalent modification feedback inhibition

saturation

An enzyme is active in the stomach of an animal but quickly loses its activity when it leaves the stomach. This example illustrates that enzymes are sensitive to changes in pH. inactivated by inhibitors in the small intestine. inactivated by movement. consumed by the quantities of substrate in the small intestine. specific to the organs in which they are produced.

sensitive to changes in pH.

What name is given to the reactants in an enzymatically catalyzed reaction? products EA active sites substrate reactors

substrate

enzyme inhibitors disrupt normal interactions between an enzyme and its_

substrate

The Michaelis constant, Km, refers to the __________ at which a reaction proceeds at __________ of the maximum velocity. This constant most accurately reflects __________. product concentration; one-half; structure of the substrate substrate concentration; one-half; the affinity of the substrate-enzyme interaction substrate concentration; one-fourth; pH optimum of the enzyme enzyme concentration; one-half; temperature optimum of the enzyme

substrate concentration; one-half; the affinity of the substrate-enzyme interaction

Saturation can be defined as a characteristic of all uncatalyzed reactions. denaturation of an enzyme. the inability to increase reaction velocity beyond a finite upper limit. inhibition of enzyme function by blocking the active site. the substrate concentration at which velocity reaches one-half maximum velocity.

the inability to increase reaction velocity beyond a finite upper limit.

As new enzymes are discovered, the EC system for naming enzymes is to be used. The names are to be based on which of the following criteria? the size of the enzyme a description of substrate function the six major classes of enzyme function an indication of the size of the substrate the name of the substrate

the six major classes of enzyme function

The expression kcat can be described as __________. The expression kcat can be described as __________. the initial velocity of an enzyme the reaction rate the substrate turnover number the Michaelis constant

the substrate turnover number

A plot of enzyme velocity against temperature for an enzyme indicates little activity at 0 degrees Celsius and 40 degrees Celsius, with peak activity at 35 degrees Celsius. The most reasonable explanation for the low velocity at 0 degrees Celsius is that __________. the enzyme was denatured at this temperature substrate binding at the active site is thermodynamically unfavorable at low temperature there is too little activation energy available from the environment the hydrogen bonds that define the enzyme's active site are broken as temperature increases

there is too little activation energy available from the environment

how can you decrease the effect of the competitive inhibitors?

they can be outcompeted by adding extra substrate

An enzyme influences the structure of which of the following? cofactor intermediate transition state substrate product

transition state

an enzyme is_(selective vs nonselective)

very selective