L6: Enzymes Flashcards
(32 cards)
1
Q
competitive inhibitor
A
- binds to substrate binding site
- competes with substrate
- binds only to the free enzyme not ES complex
- affinity of substrate decreased when inhibitor is present
- Km is increased because it takes more substrate to compete out the inhibitor
- Vmax unchanged
2
Q
noncompetitive inhibitor
A
- binds to allosteric site
- does not compete with substrate for binding to the enzyme
- binds to either enzyme or enzymes substrate complex
- Vmax decreases
- Km stays the same -substrate can still bind in same manner
- F-1,6-Bpase inhibition by AMP
3
Q
uncompetitive inhibitor
A
- binds to enzyme only after substrate has bound
- binds only to ES complex
- Km and Vmax decreased
- AchE inhibitors for Alzheimer’s
4
Q
irreversible inhibitor
A
- covalently modifies and permanently inactivates the enzymes
- Vmax decreases
- No effect on Km
- penicillin example
5
Q
general characteristics of enzymes
A
- protein catalysts
- increase rate of reaction
- recognize specific substrates and catalyze specific types of reactions
6
Q
enzymes and equilibrium constant
A
- increase rate of reaction but DO NOT CHANGE THE EQUILIBRIUM CONSTANT
7
Q
Keq > 1
A
- equilibrium favors products
8
Q
Keq < 1
A
- equilibrium favors reactants
9
Q
kcat
A
- the turnover number
- number of substrate molecules converted to product per second by a single enzyme active site
10
Q
Vmax equals
A
- kcat[E]
11
Q
enzymes and activation energy
A
- lower the activation energy of a reaction by stabilizing the transition state
12
Q
transition state
A
- the structure of a molecule as it converts from substrate to product in the enzyme-substrate complex
13
Q
Vmax
A
- the maximum velocity of an enzyme
14
Q
Km
A
- the substrate concentration that gives 1/2 the Vmax
- Michaelis-menten constant
15
Q
Michaelis mentin equation
A
v = (Vmax[S]) / (Km+S)
16
Q
Michaelis mentin plot
A
- plots substrate concentration versus velocity
17
Q
Lineweaver Burke plot
A
- inverse plot
- plots 1/substrate versus 1/velocity
18
Q
slope of line weaver burke plot
A
- slope = Km/Vmax
19
Q
isozymes
A
- normal gene underwent gene duplication to form two identical genes
- these genes underwent mutation and selection to form two or more similar genes for slightly altered enzymes
20
Q
do all duplicated genes produce functional proteins?
A
- no
21
Q
are all isozymes useful/significant?
A
- no
22
Q
allosteric enzymes
A
- have multiple active sites that are cooperative
- more sensitive to [S] than other enzymes
- give sigmoidal curve
- bind effectors at an allosteric site that is different from active site
- binding at one site changes the conformation of the enzyme, which affects affinity at the active site
23
Q
positive regulator
A
- alters the active site to allow substrate to bind more effectively
- binding of oxygen to hemoglobin
24
Q
negative regulator
A
- alters the active site to prevent binding of substrate, which decreases reaction rate
- PFK inhibition by ATP
25
when the end product level is high?
- end product acts as a negative regulator and binds to allosteric site
- substrate cannot bind to active site, and subsequent reaction stops
26
Lineweaver burke competitive inhibitor
- -1/Km moves to the right because it gets bigger
- 1/Vmax does not change
- looks like a bow tie
27
lineweaver burke noncompetitive inhibitor
- -1/Km does not change
- 1/Vmax goes further up because you are decreasing Vmax
- looks like a fan
28
line weaver burke uncompetitive
- -1/Km goes further to the left
- 1/Vmax goes further up
- Parallel lines
29
Ki
- affinity for an inhibitor
30
Poor inhibitors
- Ki > 10 uM
31
normal inhibitors
- Ki = 10 uM - 100 nM
32
excellent inhibitors
- Ki < 1 nm (tight binding)
