Enzymes Mechanisms Of Action

Question 1

Name four reasons enzymes are preferred over inorganic catalysts for biological reactions

Answer 1

Greater reaction specificity
Mild reaction conditions
Higher reaction rates
Capacity for regulation

Question 2

What type of reaction is catalyzes by oxidoreductase?

Answer 2

Transfer of electrons

Question 3

What type of reaction is catalyzes by transferases?

Answer 3

Group transfer reactions

Question 4

What type of reaction is catalyzes by hydrolases?

Answer 4

Hydrolysis reactions (transfer of functional groups to water)

Question 5

What type of reaction is catalyzed by lyases?

Answer 5

Cleavage of C-C, C-O, or C-N, or other bonds by elimation, leaving double bonds or rings

Question 6

What type of reactions are catalyzed by isomerases?

Answer 6

Transfer of groups within molecules to yield isomeric forms

Question 7

What types of reactions are catalyzed by ligases?

Answer 7

Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor.

Question 8

What is a prosthetic group?

Answer 8

Compound that is tightly and stably incorporated into a protein’s structure by covalent or noncovalent forces

Question 9

What is a cofactor?

Answer 9

Compound that binds in a transient, dissociable manner either to the enzyme or to a substrate such as ATP

Question 10

What is a coenzyme?

Answer 10

Group transfer agents that transport many substrates from one point within the cell to another

Question 11

What is the difference between an Apoenzyme and a Holoenzyme?

Answer 11

Apoenzyme - enzyme without the cofactor or prosthetic group

Holoenzyme - complete enzyme with cofactor or prosthetic group

Question 12

What three enzymes make up Pyruvate Dehydrogenase?

Answer 12

Pyruvate Dehydorgenase

Dihydrolipoyl transacetylase

Dihydrolipoyl dehydrogenase

Question 13

What coenzyme is utilized by pyruvate dehydrogenase?

Answer 13

Tiamin pyrophosphate (TPP)

It is bound to the enzyme

Question 14

What coenzymes are utilized by Dihydrolipoyl transacetylase?

Answer 14

Lipoate - covalently linked

Coenzyme A - substrate

Question 15

What coenzymes are utilized by Dihydrolipoyl Dehydrogenase?

Answer 15

FAD - bound to the enzyme

NAD - substrate for the enzyme (reduced by FADH2)

Question 16

What type of reactions are NAD and NADP involved in?

Answer 16

Redox reactions

NAD+ is an oxidizing agent (accepts electrons and becomes reduced)

Question 17

What is Pellagra and what causes it?

Answer 17

Pellegra is a skin disorder that can later cause neurological problems

Results from a dietary deficiency of Niacin

Question 18

What amino acid can Niacin be derived from?

Answer 18

Tryptophan

Question 19

What is the role of tetrahydrofolate?

Answer 19

Dontaes a Carbon in the form of -CH3, -CH2OH, or -CHO in amino acid and nucleic acid synthesis.

Question 20

What results from tetrahydrofolate deficiency?

Folic Acid Deficiency

Answer 20

Low-birth weight infant and spina bifida

Question 21

Describe the Lock and Key Model of Enzyme-substrate Interaction

Answer 21

A substrate fits perfectly into the shape of the active site, enzyme doesn’t change conformation.

Active site compliments shape and ionic properties

E.g. dihydrofolate reductase

Question 22

Describe the Induced-Fit Model of Enzyme-substrate interaction

Answer 22

Binding of substrate induces conformational change in the enzyme.

E.g. binding of D-glucose in hexokinase and Citrate Synthase

Question 23

Explain Catalysis by Proximity

Answer 23

Effective molarity and orientation of substrate molecules in the active site of enzymes will enhance the rate of reactions

E.g. substrate channeling by multi-enzyme complexes

(Pyruvate dehydrogenase)

Question 24

Explain Acid-Base Catalysis

Answer 24

Ionizable functional groups of amino acid side chains and prosthetic groups contribute to catalysis by acting as acids or bases

Question 25

Explain Catalysis by strain

Answer 25

Enzymes bind their substrates in an unfavorable conformation to waken the bond that will undergo cleavage

E.g. stickase model

Question 26

Explain Covalent Catalysis

Answer 26

Formation of a covalent bond between the enzyme and one or more substrates to create a more reactive enzyme

E.g. group transfer reactions

Usually a serine residue in the active site

Question 27

What type of catalysis is utilized by aspartic portease family enzymes?

Answer 27

Acid-Base, utilize two conserved aspartic acid residues.

E.g. Pepsin, lysosomal cathepsins, HIV protease

Question 28

What type of catalysis does Chymotrypsin utilize?

Type of Serine Protease

Answer 28

Covalent Catalysis, formation of acyl-enzyme intermediate

Acid-Base Catalysis, Asp102-His57-Ser195 at active site act as proton shuttle

Question 29

What type of Catalysis is utilized by Fructose-2,6-Bisphosphatase?

Answer 29

Covalent and Acid-Base

Question 30

Why are catalytic residues evolutionarily conserved?

Answer 30

Critical to the structure and function of proteins

Majority of disease causing mutations are mutations of these conserved catalytic residues

Question 31

What are isozymes?

Answer 31

Enzymes that catalyze the same reaction.

May differ in reaction rate, inhibition properties, electrophoretic mobility, or immunologic properties

Question 32

How are NAD+(P)-dependent dehydrogenases utilized in enzyme assays?

Answer 32

They can be coupled to other enzymatic reactions and assessed via absorbance to measure enzymatic activity.

E.g. Measurement of Hexokinase activity by coupling with G6P dehydrogenase.

Question 33

What are Enzyme-linked immunosorbent assays (ELISAs) utilized for?

Answer 33

Measure relative enzyme/protein expression.

Does not measure activity