Chapter 13 & 14- Enzyme Specificity and Kinetics Flashcards
Enzymes are _____ that increase _______ but are not _______
catalysts, reaction rate, consumed
Most enzymes are _____, except ____- which are catalytic RNA
proteins, ribozymes
What is the active site?
the pocket on the enzyme where the reaction takes place
Substrate definition
molecule bound in the active site and acted upon
How are enzymes different from ordinary chemical catalysts?
- Higher Reaction Rates
- Operate under mild reaction conditions
- Greater reaction specificity
- Capacity for Control
Enzyme-catalyzed reaction rates are _______ than with chemical catalysts
several orders of magnitude higher
Enzymes are named by adding the suffix ____
-ase
Enzymes are named for their _____
broad function
A substrate binds _____ to an enzyme at a specific site
non-covalently
Driving force of substrate binding
water release
Interactions and forces involved with substrate binding?
- Van der Waals
- Electrostatic interactions
- H-bonding
- Hydrophobic interactions
What is geometric complementarity
the substrate is complementary in shape to the active site
what is electronic complementarity
binding site attracts the substrate
Substrate specificity: of serine proteases
catalyze hydrolysis of amide bonds via a serine
Substrate specificity of Chymotrypsin
specific for a bulky hydrophobic residue
substrate specificity of trypsin
specific for a positively charged residue
substrate specificity of elastase
specific for a small neutral residue
Enzymes vary in their degree of _____
geometric specificity
characteristics of Geometric specificity of enzymes
- some are very specific
- some have more relaxed specificity
Enzymes bind ______ substrates
chiral
Enzymes catalyze reactions in a _____
stereospecific manner
Enzymes and ligands exhibit some degree of ______ fit
induced
What does induced fit mean
Enzymes change shape around the substrate when they bind and the substrate adapts to the protein
Enzymes must be complementary to the ________ state
reaction transition
Thermodynamics predict _____, it does not say anything about the _____
whether a reaction is spontaneous
rate of the reaction
Enzymes kinetics are important for:
- Elucidation of catalytic mechanism
- Role of a specific enzyme in a metabolic process
- Determine binding affinities of substrates or inhibitors to enzymes
- determine how much enzyme is present
How can the rate of a unimolecular reaction be determined?
measuring [A] or [P] as a function of time
For the reaction to occur, the existence of a high energy (unstable) complex is needed which is an _____
activated complex
The gibbs free energy of activation is also called the _____
activation barrier
Ways to increase the reaction rate
- raising the temp
- lowering gibbs free energy
Catalysts act by _____
lowering the activation barrier
The kinetic barrier is lowered by the _______ for both the forward and the reverse reactions
same amount
The equillibrium constant for the reaction _____ when catalyzed
remains the same
The slowest step in the reaction has the _____
highest activation barrier
If K1< K2 then ____
1st step is the slowest
If K1>K2 then ____
2nd step is the slowest
The slow step acts as a _____ which is the ______ of the reaction
bottleneck, rate-determining step
Assumption of steady state
substrate is in great excess over enzyme
[ES] remains ~ _______ until the substrate is nearly exhausted
constant
The rate of synthesis of ES must _____ its rate of consumption
equal
[ES] maintains a steady stade which means the change in [ES]=? not that [ES]=?
0
Vmax occurs when [S] is very ___
high
Steps to determine V0
- measure appearance of the product
- plot signal vs. time
- repeat for different [S] ([E] is the same for each experiment)
- determine d[S]/t or d[P]/t.
Km is the substrate concentration at which the reaction velocity is ______
half maximal
Km is a measure of the _____ of the enzyme for the substrate
affinity
If one step is the rate limiting step, then Kcat is ____ to the rate constant for the limiting step
equivalent
A higher value of the specificity constant means ____
a higher catalytic effeceincy
two enzymes may have the same Kcat but the rate of the uncatalyzed reactions may be ____
different
Virtual catalytic perfection def
Enzyme with Kcat/Km in thsi range must catalyze the reaction every time it encounters the substrate
