Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MCG Review > BB Lecture 9-11: Enzymes and Enzyme Kinetics I-III > Flashcards

BB Lecture 9-11: Enzymes and Enzyme Kinetics I-III Flashcards

1
Q

What is the equation for V0?

A

V0 = (Vmax [S] ) / (Km + [S] )

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the equation for Km’?

A

Km’ = Km ( 1 + [I] / Ki )

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do you calculate the extent of the change in Vmax when a non-competitive inhibitor is added?

A

Vmax’ = (Vmax) / [ 1 + ([I] / Ki) ]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are transition states and how can they be overcome?

A 
barriers to spontaneous reaction
activation energy (G)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What affects the equilibrium of a reaction?

A

delta G of the reaction (not the enzymes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the enzyme affect?

A

the reaction rate (not the equilibrium)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is Le Chatelier’s principle?

A

a change in the concentration of reactant or product will shift the equilibrium of the reactions involved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the two models for enzyme-reactant binding?

A

lock-and-key

induced-fit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the “first order” region of a reaction.

A

relationship where the initial rate (V0) is directly proportional to [S]
occurs at low substrate concentrations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe the “zero order” region of a reaction.

A

relationship where the initial rate (V0) becomes constant and the rate is independent of [S]
occurs at very high substrate concentrations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why might one enzyme (enzyme B) have a higher Vmax than another?

A
  1. enzyme B may have more than one active site for this substrate
  2. enzyme B may operate more effectively using a single active site
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can you tell the relative affinity of an enzyme for a substrate using the Michaelis-Menten plot?

A

reaching a Vmax at a relatively low substrate concentration indicates a higher affinity for substrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is Km for a reaction that shows a typical hyperbolic relationship?

A

the substrate concentration at which V0 is 50% of Vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the Michaelis-Menten equation?

A

V0 = ( Vmax [S] ) / ( Km + [S] )

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can the Michaelis-Menten equation be modified for first order behavior?

A

used if substrate concentration is much lower than Km

V0=[S]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How can the Michaelis-Menten equation be modified for sero order behavior?

A

used if substrate concentration is much higher than Km

V0=Vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the best way to determine Vmax and Km accurately?

A

Lineweave-Burke transformation (double-reciprocal transformation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the Lineweaver-Burk equation?

A

1/V0 = (Km/Vmax) x (1/[S]) + (1/Vmax)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is a competitive inhibitor?

A

compounds that are structurally similar to the substrate of an enzyme but are not the substrate and are not altered by the enzyme
compete for access to the active site

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How can a competitive inhibitor be overcome?

A

increasing substrate concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What would a competitive inhibitory do to a Lineweaver-Burk plot?

A

y-intercept (1/Vmax) will be unaffected

slope (Km/Vmax) becomes steeper resulting in a rightward shift (increase) in the x-intercept (-1/Km)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How can we use the Michaelis-Menten equation to describe the relationship between V0 and [S] in the presence of a competitive inhibitor?

A

Km’ = Km (1 + [I] / KI)
where:
[I] = concentration of the inhibitor
KI = dissociation constant of the inhibitor for its enzyme binding site

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the IC50?

A

measure of an inhibitor’s potency

half of the maximal inhibitory effect

24
Q

How can the IC50 be found graphically?

A

when plotted on a graph with [Inhibitor] (M) on the x-axis and % Inhibition on the y-axis draw a dotted line across at the point of no inhibition and at max inhibition and find the middle on the y-axis

25
Q

How can you determine the IC50 from an inhibitor’s potency?

A

IC50 = KI (1 + [S]/Km)

* Note when [S] is constant IC50 and KI are directly related

26
Q

What is a non-competitive inhibitor?

A

a compound that does not bind at the substrate-binding site (and cannot be displaced by increased [S])
interferes with enzyme’s ability to catalyze the reaction

27
Q

How does adding a non-competitive inhibitor impact a Lineweaver-Burk plot?

A

increase the y-intercept (1/Vmax)
x-intercept (-1/Km) is unchanged
slope becomes steeper

28
Q

How can you calculate the extent of the increase in 1/Vmax for a non-competitive inhibitor?

A

Vmax’ = Vmax / (1 + [I]/KI)

29
Q

What is an uncompetitive inhibitor?

A

binds after the substrate is bound to stabilize the ES complex
slows the dissociation of substrate from enzyme/formation of product

30
Q

How does adding an uncompetitive inhibitor impact a Lineweaver-Burk plot?

A

decreases Km
decreases Vmax
normally at the same magnitude
results in upward parallel displacement of the line

31
Q

What is irreversible inhibition?

A

inhibitors that form a covalent and essentially irreversible bond with the enzyme
reduces the number of functional enzyme molecules

32
Q

How does adding an irreversible inhibitor impact a Lineweaver-Burk plot?

A

decreases Vmax
does not change Km
looks like a non-competitive inhibitor

33
Q

What unique properties do irreversible inhibitors have?

A

1) as duration of exposure to the inhibitor increases, so does the number of affected enzymes, so the longer it is present the greater the reduction in Vmax
2. even if the inhibitor is removed the enzymes remain inhibited so enzymatic function can only be recovered when more enzyme is synthesized

34
Q

What is a modulator/effector?

A

i. a substrate for the enzyme (in which case the modulatory site is the same as the active site)
ii. some other molecule that acts outside the active site

35
Q

What are allosteric enzymes and how are they typically regulated?

A

enzymes that change their conformational enzemble upon the binding of an effector (allosteric modulator)
results in an apparent change in the binding affinity at a binding site

36
Q

What is homotropic modulation?

A

when the substrate is the modulator for an enzyme

enzymes regulated by this typically have multiple active sites

37
Q

What is positive cooperativity?

A

when affinity at a subsequent active site is increased by occupation of the first active site

38
Q

How can positive cooperativity in an enzyme be identified graphically?

A

sigmoidal shape (rather than hyperbolic)

39
Q

What is negative cooperativity?

A

binding of the first substrate molecule decreases affinity for catalytic action at other sites (unusual)

40
Q

What kinds of reactions do not obey Michaelis-Menten kinetics?

A

reactions that involve homotropic modulators

K0.5 replaces IC50

41
Q

What are heterotrophic modulators?

A

modulators that are not substrates of the enzyme
usually do not bind active site
readily reversible
can play a role in homeostatic control

42
Q

What kinds of enzymes are typically regulated by heterotrophic modulators?

A

rate-limiting enzymes
modulator normally synthesized many steps down stream
(if this is not the case, then the modulator normally does not help maintain homeostatic control)

43
Q

How do positive modulators (activators) work?

A

decrease Km without affecting Vmax

44
Q

How do negative modulators work?

A

produce an apparently competitive inhibitor (increases Km and no change to Vmax)
OR
apparently non-competitive inhibition (Vmax is reduced Km is unaffected)

45
Q

What is a zymogen (proenzyme)?

A

an inactive precursor of an enzyme that contains the sequence of the active enzyme and must be cleaved from the enzyme by a previous product in the pathway to become activated

46
Q

Provide examples of zymogens and why their regulation is important.

A

trypsinogen and chymotrypsinogen (often end in -ogen)
some enzymes are made in different places than where they are used and their activity would be detrimental to the place they are made, so synthesizing the inactive form and having the enzyme to activate it at the location where it is needed is favorable
it is also important for functions were an inactive form can be stored up for use in acute situations (eg. the clotting pathway)

47
Q

What are isozymes?

A

enzymes that perform the same function
reflect the fact that the same reaction may require different kinds of regulations or substrate concentrations in different tissues or cells

48
Q

What is kcat?

A

the number of operations that a single molecule of enzyme can perform per second
not intrinsic to the enzyme
dependent on the substrate the enzyme acts on

49
Q

What is the equation for the turnover number?

A

kcat = Vmax / [Et]

where [Et] is the molar quantity of enzyme present in a reaction

50
Q

How do you compare enzyme efficiency under physiological conditions?

A

specificity constant

because under physiological conditions [S] rarely approaches saturation levels, which is used to calculate kcat

51
Q

How do you calculate the specificity constant?

A

specificity constant = kcat/Km

52
Q

What does the specificity constant indicate?

A

how efficient the enzyme is when free binding sites are abundant

53
Q

What is an apoenzyme?

A

the protein component of a holoenzyme that is covalently bound to a cofactor

54
Q

What is a holoenzyme?

A

the complex of an enzyme and a cofactor

55
Q

Are all enzymes proteins?

A

No- ribosomes are enzymes composed of RNA

MCG Review (50 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions