Lecture 6 Information Flashcards
How do enzymes enhance the rate of catalysis?
stabilize the transition state
Transition state
a fleeting molecular moment in which events such as bond breakage, bond formation, and charge development are equally likely to revert to substrate or proceed to product
the transition state is transient
Why do enzymes bind to the transition state?
If enzymes binded to the ground state or lowered the energy of ES, the reaction would be less likely to occur
would take more energy to get to TS
activation energy
the difference between the energy levels of the ground state and the transition state
What types of reactions do enzymes normally catalyze?
slow, exergonic reactions
*reactions that would take place but are just too slow
Why are enzymes relatively large?
need to maintain structure of the active site
if enzymes were small, conformational changes would alter the active site more
binding energy
the total energy derived from enzyme-substrate interaction
where does binding energy come from?
1) free energy is released by forming many weak bonds and interactions between an enzyme and its substrate
2) weak interactions are optimized in the reaction transition state
how is binding energy used?
increase in free energy needed to reach the transition state is offset by the binding energy that is produced by enzyme-sustrate interactions in the transition state
binding energy functions as energy payment that lowers net activation energy and increases the speed of the reaction
does binding energy affect rate of reaction?
yes!
specificity
an enzyme’s ability to discriminate between a substrate and a competing molecule
where does an enzyme’s specificity come from?
the formation of many weak interactions between the enzyme and its specific substrate molecule
weak interactions spark both catalysis and specificity
examples of coenzymes
NAD and FAD
What are barriers binding energy can be used to overcome?
1) Entropy
2) Desolvation
3) Distortion
4) Proper alignment of the enzyme itself
Entropy and enzymes
substrates can be oriented correctly by the enzyme for reaction to occur
need to reduce entropy (by binding to enzyme) for the motion of the substrates to reduce and a reaction to occur
Desolvation and enzymes
enzyme-substrate interactions replace most or all of the hydrogen bonds with water that would otherwise impede the reaction
Induced fit
brings specific functional groups on the enzyme into the proper position to catalyze the reaction
the conformational change also permits formation of additional weak bonding interactions in the transition state
What is another way enzymes contribute to the overall catalytic mechanism besides binding energy?
covalent interactions between catalytic functional groups in the active site
Are covalent interactions between the enzyme and substrate permanent?
no
they are transient
transient
lasting for only a short period of time
impermanent
Types of covalent interactions between enzyme and substrate
1) General acid-base catalysis (donate/remove proton)
2) Covalent catalysis (create transient intermediate)
3) Metal Ion catalysis (help orient and stabilize the substrate; can mediate oxidation-reduction reactions)
Enzyme kinetics
determining the rate of a reaction and how it changes in response to changes in experimental parameters
Two steps of enzyme activity
E+S → ES (substrate binding step that usually occurs very fast)
ES –> E+P (slower second reaction that usually limits overall reaction)
What does K1 and K-1 refer to?
K1 is the forward rate of E+S → ES
K-1 is the reverse rate of E+S → ES
