Molecular recognition and Enzymes

Question 1

What are structural analogs?

Answer 1

Molecules that can occupy the same binding site on a macromolecule

Question 2

Competition does not affect extent of binding of molecules to a receptor. T/F

Answer 2

F

It decreases the chances that a particular molecule would bind to the receptor.

Question 3

Which of the following statements is/are TRUE regarding molecular recognition?

(a) It is the preferential association of molecules into complexes.
(b) It involves multiple attractive interactions between molecular surfaces.
(c) It typically involves covalent bonding between interacting molecules.
(d) All of the above
(e) (a) and (b) only

Answer 3

E

Question 4

Which of the following statements is/are TRUE regarding the complementarity of molecular surfaces in molecular recognition?

(a) It refers to the geometry of the interacting surfaces.
(b) It refers to the spatial distribution of electrical charges on the interacting surfaces.
(c) It refers to the relative sizes of the interacting molecules.
(d) All of the above
(e) (a) and (b) only

Answer 4

E

Question 5

Which of the following factor(s) influence the extent to which binding sites on a receptor are occupied by ligand?

(a) concentrations of ligand and receptor
(b) structural analogs of the ligand
(c) denaturing agents
(d) All of the above
(e) (a) and (b) only

Answer 5

D

Question 6

Which of the following processes involve(s) cellular adhesion?

(a) fertilization
(b) diapedesis
(c) migration of fibroblasts in connective tissue
(d) All of the above
(e) (a) and (b) only

Answer 6

D

Question 7

Which of the following statements is/are TRUE regarding antibodies?

(a) Each antibody molecule contains a single binding site capable of binding antigen.
(b) Antibodies typically bind to self molecules.
(c) Antibodies normally facilitate the elimination of infectious agents.
(d) All of the above
(e) (a) and (b) only

Answer 7

C

Question 8

In which of the following forms of cellular signalling is/are the target cells distant from the source of the chemical mediators?

(a) autocrine signalling
(b) paracrine signalling
(c) endocrine signalling
(d) All of the above
(e) (a) and (b) only

Answer 8

C

Question 9

Which of the following molecules can freely cross lipid bilayers of cellular membranes without the aid of macromolecular transporters?

(a) small nonpolar molecules
(b) small ions
(c) large polar molecules
(d) All of the above
(e) (a) and (b) only

Answer 9

A

Question 10

What is a zymogen?

Answer 10

The inactive precursor of an enzyme

Question 11

What are isozymes?

Answer 11

Two or more enzymes that may catalyze the same reaction

Question 12

What is the unit composed of an enzyme and a substrate?

Answer 12

Enzyme-substrate complex

Question 13

What is turnover number?

Answer 13

The maximum amount of reactions an enzyme can catalyze per unit time under a given set of conditions

Question 14

Catalytic constant is turnover number. T/F

Answer 14

T

Question 15

What does kcat stand for?

Answer 15

Catalytic constant, the maximum amount of reactions an enzyme can catalyze per unit time under a given set of conditions

Question 16

What is the binding site of an enzyme called?

Answer 16

Active site

Question 17

As the substrate concentration is increased, a greater proportion of active sites becomes occupied. T/F

Answer 17

T

Question 18

As more and more active sites are occupied by the substrate, the reaction rate increases or decreases?

Answer 18

Increases

Question 19

When is the theoretical maximum rate of an enzyme reached?

Answer 19

When all its active sites are occupied by the substrate

Question 20

What is the tendency of a substrate to bind to an active site?

Answer 20

Affinity

Question 21

What does Km stand for?

Answer 21

Michaelis-Menten constant, the concentration of substrate at which had the active sites are occupied by the substrate when affinity of active sites for substrate may be assumed constant and the conversion of product back to substrate is negligible.

Question 22

In cases wherein the affinity of active sites for substrate may assumed to be constant and the conversion of product back to substrate is negligible, what is the Michaelis-Menten constant?

Answer 22

It is the concentration of substrate at which half the active sites are occupied by substrate.

Question 23

What does a low value of Km imply about the reaction rate?

Answer 23

The reaction rate approaches the theoretical maximum even at low substrate concentrations

Question 24

What does a high value of Km imply about the reaction rate?

Answer 24

High substrate concentrations are required for the reaction rate to approach the theoretical maximum

Question 25

What are the assumptions of Michaelis-Menten constant?

Answer 25

Negligible conversion of product to substrate, and constant affinity of active site to substrate

Question 26

What is transition state stabilization?

Answer 26

The distortion of the structure of the substrate to favor the formation of the highest energy state

Question 27

What are serine proteases?

Answer 27

A large group of enzymes that each possess a serine residue side chain that directly participates in the hydrolysis of a peptide proteases

Question 28

A nonprotein component required for enzyme-mediated catalysis is known as what?

Answer 28

Cofactor

Question 29

The purely protein component of the enzyme is referred to as what?

Answer 29

Apoenzymes

Question 30

By itself, an apoenzyme can carry out catalytic activities. T/F

Answer 30

F A fully functional unit composed of apoenzyme and cofactor is necessary for carrying out catalytic activities.

Question 31

The fully functional combination of apoenzyme and cofactor is referred to as what?

Answer 31

Holoenzyme

Question 32

From where are cofactors mainly derived?

Answer 32

Nutrition

Question 33

An organic cofactor may be derived from an organic nutrient referred to as what?

Answer 33

Vitamin

Question 34

An inorganic cofactor often exists as a nutrient referred to as a what?

Answer 34

Mineral

Question 35

An organic cofactor is often referred to as what?

Answer 35

Coenzyme

Question 36

Certain coenzymes may contain a metal atom as part of their molecular structure, in which case they are described as what?

Answer 36

Organometallic.

Question 37

When a coenzyme is tightly bound to its apoenzyme (e.g., covalently bonded) it may be referred to as a what?

Answer 37

Prosthetic group.

Question 38

When is a catalytic reaction reversible?

Answer 38

If the inhibitor can readily dissociate from inhibition the enzyme or enzyme-substrate complex

Question 39

Reversible reactions are bound by covalent bonds. T/F

Answer 39

F They are bound by noncovalent bonds.

Question 40

What is the difference between competitive inhibition and allosteric inhibition?

Answer 40

Competitive inhibition decreases the affinity of the substrate by the presence of substrate analogs or transition state analogs that binding to the active site, Allosteric inhibition decreases it by the presence of inhibitors that bind to the allosteric sites.

Question 41

How does allosteric inhibition decrease affinity?

Answer 41

The binding of an inhibitor to the allosteric site changes the configuration of the active site, which prevents the substrate from binding to it

Question 42

Allosteric inhibition is noncompetitive. T/F

Answer 42

T

Question 43

What is uncompetitive inhibition?

Answer 43

When the inhibitor binds to the ES complex preferentially and decreases the turnout number by slowing down the catalytic process

Question 44

In uncompetitive inhibition, proportion of active sites occupied by substrate at a given substrate concentration may actually be higher than it would be in the absence of the inhibitor. T/F

Answer 44

T

Question 45

Inhibitor occupies active site in place of substrate (inhibitor is usually a structural analog of substrate or transition state of catalyzed reaction) Identify inhibition type and its effect on Km and kcat.

Answer 45

Competitive inhibition ``` Km= increase kcat= no effect ```

Question 46

Inhibitor binds to enzyme-substrate complex; complex is stabilized, interfering with the transformation of substrate into product Identify inhibition type and its effect on Km and kcat.

Answer 46

Uncompetitive inhibition ``` Km= decrease kcat= decrease ```

Question 47

Inhibitor binds to allosteric site (not the active site) binding of inhibitor induces conformational change in the enzyme, distorting the active site Identify inhibition type and its effect on Km and kcat.

Answer 47

Noncompetitive inhibition ``` Km= no effect kcat= decrease ```

Question 48

Enzymes that remove hydrogen atoms are called what?

Answer 48

Dehydrogenases

Question 49

Enzymes that hydrolyze proteins are called what?

Answer 49

Proteases

Question 50

Enzymes that catalyze rearrangements | in configuration are called what?

Answer 50

Isomerases

Question 51

What are the six classes of enzymes?

Answer 51

Oxidoreductases, Transferases, Hydrolases Lyases, Isomerases, Ligases

Question 52

What do oxidoreductases do?

Answer 52

Catalyze oxidations and reductions

Question 53

What do transferases do?

Answer 53

Catalyze transfer of moieties such as glycosyl, | methyl, or phosphoryl groups

Question 54

What do hydrolases do?

Answer 54

Catalyze hydrolytic cleavage of C—C, C—O, | C—N, and other bonds

Question 55

What do lyases do?

Answer 55

Catalyze cleavage of C—C, C—O, C—N, and other | bonds by atom elimination, leaving double bonds

Question 56

What do isomerases do?

Answer 56

Catalyze geometric or structural changes | within a molecule

Question 57

What do ligases do?

Answer 57

Catalyze the joining together of two molecules | coupled to the hydrolysis of ATP

Question 58

What substances are the most common prosthetic groups?

Answer 58

Metals

Question 59

What are metalloenzymes?

Answer 59

Enzymes with a tightly bound metal prosthetic group

Question 60

What do kinases do?

Answer 60

Transfer phosphate molecules

Question 61

All of the following are typical second messengers, EXCEPT: A. cAMP B. GTP C. Ca++ D. diacylglycerol

Answer 61

B

Question 62

Which of the following is the component of coenzyme? a. Vitamins b. Minerals c. Proteins d. NOTA

Answer 62

A

Question 63

Enzyme that catalyzes the isomerazation of D- alanine to Lalanine a. Racemase b. Epimerase c. Isomerase d. Mutase

Answer 63

A

Question 64

An oxidoreductase that catalyzes a reaction wherein transferred electrons are accompanied by hydrogen nuclei may be referred to as a what?

Answer 64

Dehydrogenase

Question 65

An oxidoreductase that utilizes molecular oxygen as an electron acceptor is known as a what?

Answer 65

Oxidase

Question 66

An oxidoreductase that utilizes hydrogen peroxide as the electron acceptor

Answer 66

Peroxidase

Question 67

What is an oxygenase?

Answer 67

An oxidoreductase that catalyzes the incorporation molecular oxygen into the structure of a substrate

Question 68

What are oxygenases that incorporate one atom of molecular oxygen? Both atoms of molecular oxygen?

Answer 68

Monoxygenase and dioxygenase

Question 69

An oxygenase that introduces a hydroxyl group into a substrate may be referred to as a what?

Answer 69

Hydroxylase

Question 70

Which of the following statements is/are TRUE regarding KM? (a) KM is expressed in units of concentration. (b) At a given concentration of substrate, if exactly half the active sites of an enzyme are occupied by substrate, it follows that more than half the active sites of the enzyme will be occupied by substrate if KM is somehow decreased. (c) Given two enzymes of differing KM, that with a higher KM will tend to be saturated with substrate at a higher concentration of substrate. (d) All of the above (e) (a) and (b) only

Answer 70

D

Question 71

From which of the following biochemical components are coenzymes typically derived? (a) vitamins (b) minerals (c) proteins (d) All of the above (e) (a) and (b) only

Answer 71

A

Question 72

Which of the following agents can produce enzyme inactivation? (a) strong acid (b) strong base (c) heat (d) All of the above (e) (a) and (b) only

Answer 72

D

Question 73

Which of the following statements is/are TRUE regarding enzyme inhibition? (a) Competitive inhibition is reversible while noncompetitive inhibition is irreversible. (b) Reversible inhibition typically involves covalent bond formation. (c) Competitive inhibition may be reversed by addition of excess substrate. (d) All of the above (e) (a) and (b) only

Answer 73

C

Question 74

Which of the following statements is/are TRUE regarding competitive inhibition? (a) There is an apparent increase in the value of KM. (b) The inhibitor is typically a structural analog of the substrate or transition state. (c) The inhibitor typically binds to an allosteric site. (d) All of the above (e) (a) and (b) only

Answer 74

e

Question 75

Which of the following enzymes utilize(s) molecular oxygen as an electron acceptor? (a) catalase (b) oxidase (c) peroxidase (d) All of the above (e) (a) and (b) only

Answer 75

b

Question 76

Which of the following coenzymes typically functions as a carrier for amino groups in biochemical reactions catalyzed by transferases? (a) S-adenosyl methionine (b) coenzyme A (c) pyridoxal phosphate (d) tetrahydrofolate (e) thiamine pyrophosphate

Answer 76

c

Question 77

What type of enzyme catalyzes the interconversion of the enantiomers L-alanine and D- alanine? (a) carboxylase (b) decarboxylase (c) epimerase (d) mutase (e) racemase

Answer 77

e

Question 78

Which of the following statements is/are incorrect? A. All coenzymes are cofactors B. Coenzymes are typically derived from minerals C. Coenzymes are typically derived from vitamins D. Both A and C

Answer 78

B

Question 79

Which is/are incorrect? A. Strong acids and bases tend to inactivate enzymes B. Refrigeration tends to inactivate enzymes more than heating C. Extreme heat tends to inactivate enzymes D. A & C

Answer 79

B

Question 80

Which one(s) is/are incorrect? A. Competitive Inhibition entails an increase in Km B. Noncompetitive Inhibitor is a structural analog C. Noncompetitive inhibitor binds to an active site D. B and C

Answer 80

D

Question 81

Which of the following is incorrect? A. Tetrahydrofolate typically functions as an electron carrier in redox. B. Pyridoxal Phosphate typically functions as a carrier for methyl groups C. Thiamine Pyrophosphate typically functions as a carrier for methyl, methylene, formyl and formimino groups D. All of the above

Answer 81

D

Question 82

Which of the following statements is incorrect? A. All racemases are isomerases B. Racemases catalyze interconversion of enantiomers C. Interconversion of epimers is catalyzed by a mutase D. A and B

Answer 82

C

Question 83

Which of the following is incorrect about trypsin: a. Secreted in a catalytically inactive form b. Exhibits optimum activity at normal gastric pH c. Contains a catalytic triad with a serine residue d. A and C

Answer 83

B