Chapter 6 Enzymes MasteringBio
The competitive inhibitor competes with the substrate for the ______ on the enzyme.
active site
As a result of its involvement in a reaction, an enzyme _____. permanently alters its shape. loses energy loses a phosphate group is used up is unchanged
does not change at all / remains the same
Which of the following is a mechanism of substrate activation? electron transfer bond distortion bond distortion, proton transfer, and electron transfer neutron transfer proton transfer
bond distortion, proton transfer, electron transfer
When the noncompetitive inhibitor is bonded to the enzyme, the shape of the ______ is distorted.
enzyme
A sick person often has a fever, which can inhibit the growth of bacteria because sweating removes prosthetic groups from biological enzymes. fever blocks synthesis of proteins in the bacterial nucleus. the higher temperature increases the activity of lyases. bacteria reproduce more rapidly at higher body temperature. enzymes do not function as well at temperatures other than the optimal temperature.
enzymes do not function as well at temperatures other than the optimal temperature.
The equation AB + H2O → A + B would be catalyzed by which of the following classes of enzymes? isomerases transferases oxidoreductases hydrolases ligases
hydrolases
Suggest yet another way that the rate of hydrogen peroxide decomposition can be accelerated. increase in products concentration increase in temperature increase in pressure decrease in temperature
inc in temperature
Feedback inhibition prevents cells from destroying enzymes by proteolytic cleavage when they are needed in biosynthetic pathways. irreversibly inhibiting critical enzymes. making products that are not needed by inhibiting the activity of enzymes in biosynthetic pathways allosterically. accumulating unnecessary proteins. the harmful effects of enzyme activation by covalent modification of unneeded enzymes.
making products that are not needed by inhibiting the activity of enzymes in biosynthetic pathways allosterically.
A _________ inhibitor binds to a site on the enzyme that is not the active site.
noncompetitive inhibitor
Irreversible enzyme inhibitors are _____ have only a temporary effect on enzyme activity. are uncommon in nature. are not active against ribozymes. are often toxic to cells. bind to the active site of an enzyme through noncovalent bonds.
often toxic to cells
An enzyme is a _____ catalyst. is an organic catalyst is a source of energy for endergonic reactions can bind to nearly any molecule increases the EA of a reaction is a inorganic catalyst
organic catalyst
Enzymes work by _____. reducing EA adding a phosphate group to a reactant decreasing the potential energy difference between reactant and product adding energy to a reaction increasing the potential energy difference between reactant and product
reducing activation energy (Ea)
Is the increase in temperature a suitable means of increasing reaction rates within cells? Why or why not? Not suitable; Most cells can function only within a rather limited temperature range. Suitable; That works well in living cells.
Not suitable; Most cells can function only within a rather limited temperature range
Enzymes that catalyze the phosphorylation of other enzymes are ________ ligases protein kinases oxidoreductases phosphoprotein phosphatases
Protein Kinases
In general, enzymes are what kinds of molecules? nucleic acids proteins lipids minerals carbohydrates
Proteins
A cell biologist isolates a protein-RNA complex that exhibits catalytic activity. Treatment of this complex with RNase completely abolishes catalytic activity. However, treatment of the complex with proteases results in only a 15% decrease in catalytic activity. Which of the following is the most likely explanation for these data? The catalytic activity of the complex is enhanced by the protein component and enhanced by the RNA component of the complex. The catalytic activity of the complex is independent of the protein component and only enhanced by the RNA component of the complex. The catalytic activity of the complex is enhanced by the protein component and completely dependent on the RNA component of the complex. The catalytic activity of the complex is completely dependent on the protein component and only enhanced by the RNA component of the complex.
The catalytic activity of the complex is *enhanced by the protein component* and *completely dependent on the RNA component of the complex.*
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 is an enzyme? iron ATP N-acetylmuramic acid carboxypeptidase A histidine
anything ending in -ase
An allosteric inhibitor binds at the regulatory site. is converted to an activator by the enzyme. is identical to the active site. binds and activates the high-affinity state of the enzymes. increases the rate of substrate binding.
binds at the regulatory site
An enzyme decreases the rate of a 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. changes the position of the equilibrium of the reaction.
binds substrates in a manner that facilitates the formation of product.
Explain what it means for the activation energy to be lowered from 18 to 13 kcal/mol by ferric ions but from 18 to 7 kcal/mol by catalase.
catalase provides a surface that is more conductive to rxn than ferric ions ferric ions have a surface on which the molecules are positioned such that their rxn is more favorable than when the molecules are present in solution
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
The type of inhibitor that binds to the enzyme active site is a(n) ________ inhibitor. mixed-type uncompetitive competitive coenzyme noncompetitive
competitive inhibitor
An example of an irreversible inhibitor is isoleucine. a competitive inhibitor. penicillin. angiotensin converting enzyme (ACE) inhibiting drugs. a noncompetitive inhibitor.
penicillin
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. digested in the small intestine. consumed by the quantities of substrate in the small intestine. specific to the organs in which they are produced. inactivated by movement.
sensitive to changes in pH
Enzyme inhibitors disrupt normal interactions between an enzyme and its _________
substrate
What name is given to the reactants in an enzymatically catalyzed reaction? substrate products EA active sites reactors
substrates
An enzyme reduces the free energy of ____ intermediate product cofactor product substrate transition state
transition state
Choose two properties of catalase that make it a more suitable intracellular catalyst than ferric ions. The active site of the enzyme provides a surface that is very specific for the binding of H2O2 decomposition products: H2O and O2. The active site of the enzyme provides a surface that is very specific for the binding of H2O2 molecules. The enzyme is insensitive to temperature changes. The active site of the enzyme favors maximally the decomposition of H2O2 molecules.
1. active site of enzyme provides a surface that is very specific for the binding of H2O2 molecules 2. active site of the enzyme favors maximally the decomp of H2O2 molecules
The enzyme phosphofructokinase (PFK) from E. coli is a tetrameric enzyme that allosterically binds AMP. The binding of AMP increases the affinity of the substrates for the active site of PFK. Which of the following is true concerning this system? AMP is a competitive inhibitor. AMP is an allosteric inhibitor and will stabilize PFK in a conformation that will require more substrate to achieve 1/2 Vmax. AMP is an allosteric activator and will stabilize PFK in a conformation that will require less substrate to achieve 1/2 Vmax. AMP is a cofactor/coenzyme for PFK and is absolutely required for PFK activity.
AMP is an allosteric activator and will stabilize PFK in a conformation that *will require less substrate to achieve 1/2 Vmax.*
Which of the following is not true of the enzyme - substrate interaction? Many enzymes are extremely specific regarding a substrate. Some enzymes accept any of a whole group of substrates. Cells are often able to carry out metabolic activity with only a handful of enzymes because many are nonspecific. Many enzymes cannot recognize a stereoisomer of their substrate. Carboxypeptidase recognizes any of the amino acids from the carboxyl end of a polypeptide.
Cells are often able to carry out metabolic activity with only a handful of enzymes because many are nonspecific.
What is the correct label for "A"? ATP enzyme energy energy of activation uphill substrate energy
Energy of activation
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 __________. feedback regulation competitive inhibition covalent modification irreversible inhibition
Feedback Regulation
The site on an enzyme that will bind the substrate is called the metastable site. prosthetic group. active site. catalyst. activation site.
active site
Which of the following is true of an enzyme? An enzyme __________. is always a protein supplies energy to start a chemical reaction acts as a biological catalyst is nonspecific
acts as a biological catalyst
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 rxn rate
Ribozymes were discovered ________ protein enzymes, even though they ________. after; catalyze many important cellular reactions at the same time as; only catalyze one type of cellular reaction before; are more heat labile than protein enzymes after; are the only catalysts found in bacteria and archaea before; only catalyze one type of cellular reaction
after; catalyze many important cellular reactions
The induced-fit model distorts the shape of the enzyme and the substrate. is also called the lock-and-key model. was proposed by Hans Buchner. states that enzyme - substrate interactions are rigid. proposes that very strong covalent bonds are formed upon substrate binding.
distorts the shape of the enzyme and the substrate.
The rate of a reaction catalyzed by an enzymes usually ________ with temperature; however, at temperatures above the optimum range ________. decreases; the reaction proceeds without the enzyme increases; protein denaturation occurs increases; the direction of the reaction reverses increases; the reaction proceeds without the enzyme decreases; prosthetic groups are necessary
increases; protein denaturation occurs
The active site for many enzymes involves amino acids that are brought into close proximity by extensive protein folding. may require a prosthetic group such as a metal ion. contains amino acids that are contiguous to one another along the primary sequence of the protein. involves amino acids that are brought into close proximity by extensive protein folding and may require a prosthetic group such as a metal ion. usually depends on only one amino acid.
involves amino acids that are brought into close proximity by extensive protein folding may require a prosthetic group such as a metal ion.
Usually, ______ 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 inhibitor
Which of the following is an example of a prosthetic group? a polypeptide chain a glycine residue a zinc ion a hydrogen ion carboxypeptidase A
zinc ion
