Enzymes Flashcards
Biochemists are interested in enzyme kinetics because…
- elucidation of catalytic mechanisms
- understanding the roles of enzymes
within metabolic processes. - optimization of enzyme-catalyzed
processes (PCR, chemical synthesis,
ethanol production, etc).
Kinetics is concerned with…
the rates of chemical
reaction.
– Enzyme kinetics addresses the biological roles of
enzymatic catalysts and quantifies the remarkable
functions of biological enzymes
Enzyme kinetics information can be exploited…
– to control and manipulate the course of metabolic events
- Pharmaceuticals or drugs are often special inhibitors targeted at a particular enzyme.
– the science of pharmacology relies on such information
Enzymes:
- Living organisms must be able to carry out
chemical reactions which are
thermodynamically very unfavorable.
– Break and form covalent bonds
– Move large structures
– Effect three dimensional structure
– Regulate gene expression
- They do so through enzyme catalysis
Enzymes can have massive effects:
- Most common biological reactions can take
place without enzyme catalysis
– Can take 750,000,000 years
- Versus: With enzyme 22 milliseconds
- A bag of sugar can be stored for years with
very little conversion to CO2
and H2O
– Yet this conversion is basic to life
– When sucrose is consumed by cells, it is
converted to chemical energy very fast
Catalysis carried out by…
very highly specialized class of proteins: Enzymes
– Specialized to perform specific chemical
reactions
– Specialized to work in specific environments
Enzymes have immense importance in…
a number of
fields.
– Genetic diseases are frequently defects in enzymes or increased/decreased levels of enzymes
- Important diagnostic tools
– Drugs exert effects by interacting with enzymes
- MAO inhibitors
– Used in food processing and in chemical industry
– Enzyme inhibitors are a foundation of biological
weapons
Hydrolysis of ATP is…
thermodynamically favorable but ATP is kinetically stable
Transition state =
intermediate chemical state Required for reactants to form products = higher energy than reactants
Activation energy (EA
) =
minimum energy required to form transition state
Number of molecules possessing energy > EA =
numbers of molecules able to form product
Number of molecules possessing energy > EA =
numbers of molecules able to form product
Life depends upon the…
high activation
energies that prevent most cellular
reactions occurring at appreciable rates
without a catalyst.
-Allows reactions to
be regulated.
Enzymes accelerate reactions by…
decreasing G‡.
- Catalysts get the reaction to the equilibrium faster, but don’t affect Keq
Biological catalysts / Enzymes do NOT…
change direction of reaction
- DO increase the rate of reaction by
lowering EA - Form transient complex with substrate(substrate = substance upon which an enzyme acts)
Catalysis occurs at the…
active site.
Active site:
- Substrate binds to enzyme at active site
- Usually groove or pocket
- Substrate fits with high specificity
- Usually only 5% of protein
- Amino acids in active site often not contiguous
Enzymes are sophisticated
catalysts (4)
- Active Site
– Is complementary in shape
and functionality with the
substrate. - Catalytic Efficiency
– Rate increased 103
-108 - Specificity
– Reactions are extremely
specific in both the substrates
and the products. - Regulation
Kinetics Is the science that describes…
the properties of a chemical reaction including those mediated by enzymes (catalysis)
Kinetics measures…
the concentration of substrate
and/or products of a reaction to determine the velocity of the reaction
- Measures the effects of concentration,
temperature, pH, etc. to characterize the
properties of the enzyme catalyzing the
reaction
Enzyme Kinetics Is…
- An approach to understanding the mechanism of action of enzymes
- An approach to understanding how mutations may effect function
- An approach to understanding how changes in the
physical and chemical environments change function
Enzymes Do…
- Lower energy of activation of forward
and reverse reactions - Reduce the time required to reach equilibrium
- Stabilize the Transition State
- Conduct a specific reaction with no side products
Enzymes Don’t…
- Change the ΔG of a Reaction
- Change the Equilibrium Position of a Reaction
- Change the Energy Yield
(or requirement) of a Reaction
Enzyme Definition:
A protein (or RNA) molecule that has the property of a catalyst, sometimes called a
biocatalyst.
Substrate Defnition:
The target of the enzyme’s action. The molecule that will undergo chemical change as a result of the enzyme.
Enzyme activity definition:
A measure of the enzyme’s
catalytic effectiveness as manifested by the rate of the reaction catalyzed.
Cofactor Definition:
A component that works with the enzyme in effecting catalysis. Any chemical factors that assist the activity of an enzyme-catalyzed reaction.
Coenzyme Definition:
Related to cofactor, but generally used to describe molecules that are derived from B-vitamins.
Enzyme kinetics Definition:
A branch of enzymology that deals with mechanism as studied by factors that affect the
rate of enzyme reactions.
Active Site Definition:
That region on the enzyme surface or
within a crevice where the substrate binds and
catalysis is performed.
