Chapter 4 - Enzymes

Question 1

hydrolase

Answer 1

hydrolyzes chemical bonds (ex. ATPase, proteases)

Question 2

isomerase

Answer 2

rearranges bonds within a molecule to form an isomer

Question 3

ligase

Answer 3

forms a chemical bond (ex. DNA ligase)

Question 4

lyase

Answer 4

breaks chemical bonds by means other than oxidation or hydrolysis

Question 5

kinase

Answer 5

transfers a phosphate group to a molecule from a high energy carrier, such as ATP

Question 6

oxidoreductase

Answer 6

runs redox reactions

Question 7

polymerase

Answer 7

polymerization (ex. addition of nucelotides to the leading strand of DNA)

Question 8

phosphatase

Answer 8

removes a phosphate group from a molecule

Question 9

protease

Answer 9

hydrolyzes peptide bonds

Question 10

reaction coupling

Answer 10

one very favorable reaction is used to drive an unfavorable reaction

Question 11

free energy changes are ____

Answer 11

additive

Question 12

active site

Answer 12

region in an enzyme’s three dimensional structure that is directly involved in catalysis

Question 13

enzymes are usually ____ shaped

Answer 13

globular/spherical

Question 14

substrates

Answer 14

reactants in an enzyme-catalyzed reaction

Question 15

active site model

Answer 15

substrate and active site are perfectly complementary

Question 16

induced fit model

Answer 16

substrate and active site differ slightly in structure and that the binding of the subtrate induces a conformational change in the enzyme

Question 17

recognition pocket

Answer 17

pocket in the enzyme’s structure which attracts certain residues on substrate polypeptides

Question 18

enzymes that act on hydrophobic substrates have ___ amino acids in their active sites

Answer 18

hydrophobic

Question 19

both ____ and ____ play critical roles in enzymatic function

Answer 19

temperature and pH

Question 20

cofactors

Answer 20

metal ions or small molecules required for activity in many enzymes (ex. vitamins)

Question 21

coenzyme

Answer 21

organic cofactors that often bind to the substrate during the catalyzed reaction

Question 22

4 types of enzyme activity regulation

Answer 22

1) covalent modification
2) proteolytic cleavage
3) association with other polypeptides
4) allosteric regulation

Question 23

covalent modification

Answer 23

phosphorylation through covalent bonds that either activate or inactivate the enzyme (ex. hydroxyl group on serine)

Question 24

proteolytic cleavage

Answer 24

inactive forms of enzymes (zymogens) become activated by cleavage by a protease

Question 25

association with other polypeptides

Answer 25

association with other polypeptides that affect enzyme activity

Question 26

constitutive activity

Answer 26

continuous rapid catalysis

Question 27

allosteric regulation

Answer 27

binding of small molecules to particular sites on an enzyme that are distinct from the active site; alters conformation which can increase or decrease catalysis

Question 28

allosteric regulation is usually ___ and ___

Answer 28

noncovalent; reversible

Question 29

feedfoward stimulation

Answer 29

stimulation of an enzyme by its substrate

Question 30

enzymes can act as ___ because they can regulate flow of substrates into products

Answer 30

valves

Question 31

enzyme kinetics

Answer 31

study of rate of formation of products from substrates in the presence of an enzyme

Question 32

reaction rate

Answer 32

amount of product formed per unit time in mol/s

Question 33

reaction rate depends on concentration of ___ and ___

Answer 33

substrate; enzyme

Question 34

if we double amount of substrate then the reaction rate ___

Answer 34

doubles

Question 35

point of saturation

Answer 35

adding more substrate will not increase reaction rate at all; denoted as Vmax

Question 36

Km

Answer 36

substrate concentration at which the reaction velocity is half its maxium

Question 37

if enzyme-substrate pair has a low Km then ___

Answer 37

enzyme has high affinity for that particular substrate

Question 38

positive cooperativity

Answer 38

binding of a substrate to one subunit increase affinity for rest of the subunits; binding occurs at active sites

Question 39

sigmoidal curve results from ____

Answer 39

positive cooperative binding

Question 40

4 types of inhibition of enzyme activity

Answer 40

1) competitive
2) noncompetitive
3) uncompetitive
4) mixed-type

Question 41

competitive inhibition

Answer 41

• molecules compete with subtrate for binding at active site
• can be overcome by excess substrate
• does not affect Vmax

Question 42

noncompetitive inhibition

Answer 42

• bind at an allosteric site
• cannot be overcome by excess substrate
• lowers Vmax; doesn’t affect Km

Question 43

uncompetitive inhibition

Answer 43

• inhibitor can only bind to enzyme-substrate complex
• binds to allosteric sites; lowers Vmax
• decreases Km

Question 44

mixed-type inhibition

Answer 44

• inhibitor can bind to either free enzyme or enzyme-substrate complex
• if enzyme has greater affinity for the inhibitor in its free form, Km increases
• if enzyme has greater affinity for the inhibitor in its complex form, Km decreases
• lowers Vmax

Question 45

lineweaver-burk plot

Answer 45

• slope is Km/Vmax
• y-intercept is 1/Vmax
• x-intercept is -1/Km

Question 46

when there is increasing concentrations of a competitive inhibitor then the lines will intersect along the ___

Answer 46

y-axis

Question 47

when there is an increase in concentration of non-competitive inhibitor the lines will intersect on the ___

Answer 47

x-axis