CHAPTER 6 Flashcards
(101 cards)
1
Q
biological catalysts
most biochemical reactions would not proceed at the required rate w/out it
A
Enzymes
2
Q
dynamic and essential role in the cell
extraordinary catalytic power
selective
A
Enzymes
3
Q
Classes of Enzyme Specificity
A
Absolute
Group
Linkage
Stereochemical
4
Q
Classes of Enzyme Specificity
enzyme reacts with only one substrate
A
Absolute
5
Q
Classes of Enzyme Specificity
enzyme catalyzes reaction involving any molecules with the same functional group
A
Group
6
Q
Classes of Enzyme Specificity
enzyme catalyzes the formation or break up of only certain category or type of bond
A
Linkage
7
Q
Classes of Enzyme Specificity
enzyme recognizes only one of two enantiomers
A
Stereochemical
8
Q
a biological catalyst
A
Enzyme
9
Q
with the exception of some RNAs that catalyze their own splicing, all enzymes are
A
proteins
10
Q
can increase the rate of a reaction by a factor of up to 1020 over an uncatalyzed reaction
A
enzymes
11
Q
some enzymes are so specific that they catalyze the reaction of only one _____________; others catalyze a family of similar reactions
A
stereoisomer
12
Q
The rate of an enzyme’s reaction depends on its
A
activation energy or ΔG°‡
13
Q
an enzyme provides an alternative pathway with a __________ activation energy
A
lower
14
Q
a reaction that releases free energy, the reactants have more energy than the products, is spontaneous
A
exergonic
15
Q
what happens in a catalyzed reaction
A
it speeds up the reaction without being consumed or altered by the reaction. Catalysts make it easier for atoms to break and form new bonds, which creates new substances. It decreases the activation energy.
16
Q
For a reaction taking place at constant temperature and pressure, e.g., in the body, what would be the equation
A
A ⇌ B
17
Q
the change in free energy is
A
ΔG° = ΔH° - TΔS°
18
Q
Difference in energies between initial state and final state formula, relates the standard free energy change (ΔGo) to the equilibrium constant (Keq)
A
ΔGo = −RTlnKeq
19
Q
Gibbs free energy
The change in enthalpy, or the amount of heat absorbed or released during a reaction at constant pressure
A
ΔH°
20
Q
Gibbs free energy
The change in entropy multiplied by the temperature
A
TΔS°
21
Q
Gibbs free energy
The natural logarithm of the equilibrium constant
A
lnKeq
21
Q
Gibbs free energy
The ideal gas constant, which is multiplied with the temp in kelvin
A
R = 8.314 J/K⋅mol
RT
22
Q
what relationship does ΔG and Keq have
A
inversely related, where if ΔG is positive, Keq is negative
23
Q
if ΔG is positive, then the reaction is
A
non-spontaneous
24
if ΔG is negative, then the reaction is
spontaneous
25
If the equilibrium favors the product, the the Keq is ______
and the product of the reaction has ___ energy
higher
26
Catalyzed vs uncatalyzed reaction graphs
Catalyzed - linear, conc of substrate vs velocity
uncatalyzed - hyperbolic, conc of substrate vs velocity, rate of reaction plateaus at the end
27
Catalyzed vs uncatalyzed reaction graphs in ordered reactions
Catalyzed - first order reaction
uncatalyzed - first order reaction, zero order reaction
28
why do enzymes reach a maximum reaction rate?
enzymes that are limited in numbers can be overrun by an increasing number of substrate
29
How does temperature help catalyze reaction
The increasing heat can help with increase of kinetic energy and the collision of particles in the solution
Increasing temperature will eventually lead to protein denaturation
29
Temperature can also catalyze reaction (increase rate)
true
30
the sum of the exponents in the rate equation
Order of reaction
31
the small portion of the enzyme surface where the substrate(s) becomes bound by noncovalent forces, e.g., hydrogen bonding, electrostatic attractions, van der Waals attractions
Active site
31
The reaction is said to be first order in A, first order in B, and second order overall
rate = k [A]1 [B]1
31
In an enzyme-catalyzed reaction, the product is an
enzyme substrate process
31
advantage: Linear
disadvantage: the data points are compressed in the high substrate concentration region
Lineweaver-Burk
31
the enzyme undergoes a conformational change upon binding to substrate. The shape of the active site becomes complementary to the shape of the substrate only after the substrate binds to the enzyme.
induced- t model
31
the shape of the substrate and the conformation of the active site are complementary to one another.
Lock-and-key model
32
known as the double reciprocal plot
Lineweaver-Burk
32
Binding Models
substrate binds to that portion of the enzyme with a complementary shape
Lock-and-key model
32
Binding Models
binding of the substrate induces a change in the conformation of the enzyme that results in a complementary fit
Induced fit model
32
Two models have been developed to describe formation of the enzyme-substrate complex
Lock-and-key model
Induced fit model
32
Michaelis–Menten graph form
should be hyperbolic in shape
32
A particularly useful model for the kinetics of enzyme-catalyzed reactions was devised in 1913
Initial rate of an enzyme-catalyzed reaction versus substrate concentration
Michaelis–Menten
32
disadvantage: not linear
Vmax approximately the asymptote (error)
Km depends on Vmax (another error)
Michaelis-Menten Model
32
Lineweaver-Burk shape
linear or sigmoidal
32
turnover number
Turnover Numbers
33
is the substrate concentration that leads to an initial velocity of Vmax/2
the substrate concentration that results in the filling of one-half of the enzyme active sites
Km
33
Km value where it requires high substrate concentration to achieve a given velocity
large Km
33
A small km indicates a ___ ES binding
strong binding between E & S
33
A large km indicates a ___ ES binding
weak interaction between E & S
33
number of substrate molecules transformed to product by one enzyme molecule per unit time (min or s) ~for an enzyme w/ 1 active site
measure of the efficiency of an enzyme
K3
33
is equivalent to the dissociation constant of the ES complex
Km
33
Vmax is related to the turnover number of enzyme:also called
kcat
33
Km equations
Km=k2/k1
Km = (k2+k3)/k1
33
an increase of kcat or Km indicates
more efficient enzyme
33
a direct measure of enzyme efficiency and specificity
shows what the enzyme and substrate can accomplish when abundant enzyme sites are available
allows direct comparison of the effectiveness of an enzyme towards different substrate
kcat/KM
33
examplez of irreversible inhibitors
suicide and trojan horse
33
types of Reversible inhibitor
competitive inhibitor
noncompetitive inhibitor
33
types of Inhibition of Enzyme Activity
competitive
noncompetitive
uncompetitive
33
Enzyme Inhibition
a substance that binds to an enzyme to inhibit it, but can be released
Reversible inhibitor
33
what Chymotrypsin catalyzes
The selective hydrolysis of peptide bonds where the carboxyl is contributed by Phe and Tyr
It also catalyzes hydrolysis of the ester bonds
33
nonsubstrate molecules may interact w/ enzymes
dec in enzymatic activity
reveals mechanism of enzyme action
Inhibition of Enzyme Activity
34
if there is very little enzyme and a saturating amount of substrate, then all of the enzyme molecules are bound to substrate. Adding more substrate under this condition will __________ the rate of reaction.
not increase
34
when reactants are added, what side of does the equation shift to
shifts to the left
34
effect of ph on eznymes
significantly affects enzyme activity, where each enzyme has an optimal pH level at which it functions best; deviating from this optimal pH, either too acidic or too alkaline, can drastically reduce enzym
34
a substance that causes inhibition that cannot be reversed
usually involves formation or breaking of covalent bonds to or on the enzyme
Irreversible inhibitor
34
similar in structure to the substrate
inhibitor cannot be converted to a product
binds to the active (catalytic) site and blocks access to it by substrate
Competitive inhibitor
34
does not bind in the active site, binds at some other region
binding converts the enzyme to a nonfunctional conformational state, substrate still fully capable of binding on the active site, but is not converted to product
Several equilibria are involved
Noncompetitive inhibitor
34
Enzymes speed up the reaction rate by creating a situation where the distance between the ______________ on an energy diagram is reduced.
transition state and the ES complex
35
similar in structure to the substrate
inhibitor cannot be converted to a product
binds to the active (catalytic) site and blocks access to it by substrate
Competitive inhibitor
35
inhibitor can bind to the ES complex but not to free E. Vmax decreases and Km decreases.
Uncompetitive
35
dissociation constant, KI for EI
EI ⇌ I + E, KI =[E][I]/[EI]
35
In o-diphenol oxidase, what type of inhibition happens when it binds to a copper atom in the enzyme which is essential for its activity
noncompetitive
35
Substrate must compete with inhibitor for the active site; more substrate is required to reach a given reaction velocity
Competitive Inhibition
35
Because the inhibitor does not interfere with binding of substrate to the active site, KM is unchanged
Increasing substrate concentration cannot overcome noncompetitive inhibition
Noncompetitive inhibitor
35
Similar to noncompetitively, but binding of I affects binding of S and vice versa.
Mixed
35
Noncompetitive Inhibition the maximum velocity Vmax has the form
VI max = Vmax/1+[I]/Ki
35
when products are added, what side of does the equation shift to
shifts to the right
35
A Lineweaver-Burke Plot for Competitive Inhibition
Vmax same
Km Increase
36
A Lineweaver-Burke Plot for Uncompetitive Inhibition
Vmax decrease
Km decrease
36
In o-diphenol oxidase, what type of inhibition happens when it binds the same site as catechol but is not acted upon
competitive
36
A Lineweaver-Burke Plot for Noncompetitive Inhibition
Km unchanged
Vmax decreases
36
Rate of product formation decreases with time as it has the
decrease in substrate concentration
denaturation of the enzyme
product inhibition of the reaction
reversion of the product to substrate
36
Thermodynamic spontaneity cannot tell us whether are action will be
fast
36
The speed of a reaction is a kinetic property controlled by the nature of the energy state of the
ES complex and the transition state
37
A chemical reaction may go faster at higher temperatures.
However, when the reaction is catalyzed by an enzyme,
this is true only for a specific range of temperatures.
true
37
In many situations, the concentration of the reactants does influence the _________ of an enzyme-catalyzed reaction
rate
37
when adding too much substrate, the enzyme is already working at its
____________ and is exhibiting ___________
Vmax
zero-order kinetics
37
KM and Vmax can be estimated by a more accurate way is to make a Lineweaver Burk plot of
1/V versus 1/[S]
38
Km that indicates a high affinity
low KM
38
KM and Vmax can be estimated by plotting the
velocity versus [S] graph
39
Enzymes and substrates are attracted to each other via
noncovalent interactions, such as electrostatic attractions
39
An energy diagram will show that the energy of the ES complex is _________ than the energy of the E + S alone
less
39
The active site of an enzyme has amino acids in a specific orientation where they can __________ to the substrate.
bind
40
is equal to the substrate concentration that yields a velocity of Vmax/2
crude measure of the affinity between the enzyme and substrate
KM
40
nonallosteric enzyme and exhibits hyperbolic kinetics.
Chymotrypsin
40
is an allosteric enzyme. It has multiple subunits, and the binding of one molecule of substrate affects the binding of the next molecule of substrate.
ATCase
41
Irreversible Inhibition that is important drugs in medicine and are used to study enzyme mechanisms.
Suicide substrates
41
tells us how fast the enzyme can generate product under saturating substrate conditions.
Vmax
41
is an irreversible inhibitor. It binds co valently to the enzyme inactivating it.
suicide substrate
