3.2

Question 1

activation energy

Answer 1

amount of energy required to start a reaction
changes reactants to transition state
comes from heat energy

Question 2

transition state

Answer 2

highest energy state
reactant molecules must collide with enough energy to react

Question 3

rate of reaction factors

Answer 3

concentration of reactants
kinetic energy of reactants (function of temperature)
activation energy

Question 4

enzymes

Answer 4

-biological catalysts that increase the rate of reaction by lowering the activation energy
-Ea(uncatalyzed)>Ea(catalyzed)
-ΔG(uncatalyzed)=ΔG(catalyzed)
-spontaneous reactions do not necessarily occur quickly
-lower the energy barrier that bring reactants closer together

Question 5

enzymes resemble…

Answer 5

proteins
RNA catalysts - ribozymes

Question 6

enzyme specificity

Answer 6

determine by precise interlocking of the enzyme + substrate w/ interaction between their chemical groups

Question 7

active site

Answer 7

specific 3D location on the enzyme where catalysis takes place
3D structure and chemical properties of the enzyme active site determines its specificity

Question 8

substrate

Answer 8

reactants in enzyme-catalyzed reactions

Question 9

enzyme-substrate (ES) complex

Answer 9

held together by noncovalent or temporary, covalent bonds
the enzyme may change shape while bound to the substrates but returns to its original form
E + S –> ES – E + P

Question 10

induced fit

Answer 10

an enzyme may undergo a conformation change upon binding its substrate to the active site
-a substrate doesn’t need to fit exactly in the active site
-brings reactive side chains into alignment with the substrate
-excludes non-substrate H2O (so that it does not interfere with the reaction)

Question 11

cofactors

Answer 11

many enzymes require nonprotein chemical partners to function

Question 12

inorganic cofactors

Answer 12

inorganic ions (Fe2+, Cu+)

Question 13

organic cofactors

Answer 13

non-amino acid “organic” molecules
coenzymes - reversibly interact with enzymes
prosthetic enzymes - permanently bound to enzymes

Question 14

rate of enzyme-catalyzed reactions

Answer 14

depends on substrate concentration until all enzymes are occupied
at low [S], the presence of an enzyme greatly increases the reaction rate
at high [S] and [S]>[E], all enzymes are bound to substrates, it is working at maximum rate, active sites are saturated
rate of the uncatalyzed reaction is proportional to [S]

Question 15

oxidoreductors

Answer 15

transfer electrons between molecules

Question 16

transferases

Answer 16

transfer functional groups between molecules

Question 17

hydrolases

Answer 17

add water to covalent bonds to break down molecules

Question 18

lyases

Answer 18

catalyzed non-hydrolytic bond breakages

Question 19

isomerases

Answer 19

move functional groups within a single molecule

Question 20

ligases

Answer 20

join two molecules together by forming a new covalent bond

Question 21

translocases

Answer 21

catalyze the movement of ions or molecules across the membrane

Question 22

enzyme mechansims

Answer 22

an enzyme may use one or more mechanisms to facilitate the formation of the transition state and lower the Ea
-orientation
-physical strain
-modification of chemical groups

Question 23

orientation

Answer 23

enzymes bring substrates together and in the right orientation to react

Question 24

physical strain

Answer 24

enzymes induce strain on the substrates, making bonds unstable and more reactive to other substrates

Question 25

modification of chemical groups

Answer 25

enzymes make substrate(s) more reactive by altering charge or forming a temporary covalent bond with substrate(s)

Question 26

rate of metabolic pathways

Answer 26

can be regulated by regulating key enzymes in response to the metabolic needs of the cells -regulation of gene expression (concentration of enzyme molecules) -regulation of enzyme activity (reversible inhibition, allosteric regulation, covalent modification)

Question 27

enzyme activity

Answer 27

can be regulated (activated or unactivated) in response to cellular conditions

Question 28

irreversible inhibition

Answer 28

inhibitor covalently bonds to the active site and permanently inactivates the enzyme ex: aspirin inactivating the COX enzyme

Question 29

reversible inhibition

Answer 29

inhibitor noncovalently binds to the enzyme and slows reaction rate competitive and uncompetitive inhibitors

Question 30

competitive inhibititors

Answer 30

binds to the active site, prevent binding of the substrate, resembles the substrate

Question 31

uncompetitive inhibitors

Answer 31

bind to the ES complex, prevent formation or release of products

Question 32

allosteric enzymes

Answer 32

made up of multiple polypeptide subunits with quaternary structure catalytic subunits contain an active site regulatory subunits contain allosteric sites active and inactive forms can be converted

Question 33

allosteric regulation

Answer 33

occurs when a molecule causes a change in enzyme shape by binding to the enzyme at a location other than the active site

Question 34

inactive form

Answer 34

binding of an inhibitor stabilizes the inactive form no product formation

Question 35

active form

Answer 35

the change in shape alters substrate binding affinity and the rate of the reaction binding of the activator stabilizes the active form product formation

Question 36

rate of reaction (allosteric enzyme)

Answer 36

for an allosteric enzyme with multiple active sites, substrate binding at one site changes the affinity of another site for a substrate

Question 37

feedback inhibition

Answer 37

allosteric enzymes are often found in metabolic pathways that display feedback inhibition the final product acts as an inhibitor of the first enzyme, which shuts the pathway down when there is an excess of the product

Question 38

covalent modification

Answer 38

many enzymes are regulated through reversible phosphorylation (can turn the enzyme on and off)

Question 39

enzyme function

Answer 39

enzymes have an optimal temperature and pH