Enzymes Flashcards
Exergonic Rxns:
: Release energy; delta G is negative
Endergonic Rxns:
: Require energy; delta G is positive
Oxidoreductases:
: REDOX reactions that involve the transfer of e-
Transferases:
Move a functional group from one molecule to another
Hydrolases:
Catalyze cleavage with the addition of H2O
Lyases
Catalyze cleavage without the addition of H2O and
without the transfer of e-
. The reverse reaction
(synthesis) is often more important biologically.
Isomerases
Catalyze the interconversion of isomers, including both
constitutional isomers and stereoisomers.
Ligases
Join two large biomolecules, often of the same type.
Lipases:
Catalyze the hydrolysis of fats. Dietary fats are broken
down into fatty acids and glycerol or other alcohols.
Kinases:
ADD a phosphate group. A type of transferase
Phosphatases:
: REMOVE a phosphate group. A type of transferase
Phosphorylases:
Introduces a phosphate group into an organic molecule,
notably glucose.
Saturation kinetics
As the substrate concentration increases the reaction rate with increase until a maximum value is reached
Michaelis menten plot
Hyperbolic curve
Michaelis menten lineweaver burk plot
Line
What is the km?
The substrate concentration when the enzyme runs half of its Vmax
Vmax
The maximum rate at which an enzyme can catalyze a
reaction. This is when all enzyme active sites are
saturated with substrate.
Michaelis Menten equation
Vo = ((Vmax) [S]))/ [S] + Km
Cooperative enzyme graph
Sigmoidal curve because of the change in activity with substrate binding
Mechanism of Enzyme Activity
Enzymes act by stabilizing the transition state, providing a favorable
microenvironment, or bonding with the substrate molecules.
Active Site
The site of catalysis
Lock & Key Theory
The enzyme and substrate are exactly complementary
and fit together like a key into a lock.
Induced Fit Theory:
The enzyme and substrate undergo conformational
changes to interact fully
Cofactors:
Metal cation that is required by some enzymes
Coenzyme
Organic molecule that is required by some enzymes
Properties that effect enzymes
Temperature and pH can denature proteins and salinity can impact the action of enzymes
Feedback Inhibition:
An enzyme is inhibited by high levels of a product
from later in the same pathway.
Reversible
Inhibition:
The ability to replace the inhibitor with a compound
of greater affinity or to remove it using mild
laboratory treatment
Where do competitive inhibitors bind?
Active site
How is the Vmax and Km affected by a competitive inhibitor?
Vmax is unchanged and Km increases
What does a lineweaver burk graph look like for competitive inhibitors?
The y intercept is the same but the competitive inhibitor has a steeper slope
Competitive
Inhibition:
When the inhibitor is similar to the substrate and
binds at the active site, blocking the substrate from
binding. Can be overcome by adding more substrate.
Vmax is unchanged, Km increases.
Uncompetitive
Inhibition definition and its effect on vmax and km
When the inhibitor binds only with the enzyme substrate complex. Vmax and Km both decrease.
Noncompetitive inhibition definition and its effects on both the vmax and the km
When the inhibitor binds with equal affinity to the
enzyme and the enzyme-substrate complex. Vmax
decreases, Km is unchanged.
What does a lineweaver burk graph look like for uncompetitive inhibition?
Lineweaver burk noncompetitive inhibition
Mixed Inhibition
When the inhibitor binds with unequal affinity to the enzyme and the enzyme-complex. Vmax decreases, Km is increased or decreased depending on if the inhibitor has a higher affinity for the enzyme or enzyme-substrate complex.
Irreversible Inhibition
Alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently.
Suicide Inhibitor
A substrate analogue that binds IRREVSERIBLY to the active site via a covalent bond
Allosteric Effecter:
: Binds at the allosteric site and induces a change in the conformation of the enzyme so the substrate can no longer bind to the active site. Displays cooperativity, so it does not obey Michaelis-Menten kinetic
Positive Effectors
Exert a positive effect, increase enzyme activity
Negative effectors
Exert a negative effect and decrease activity
Homotropic Effector:
An allosteric regulator that IS ALSO the substrate. Ex: O2 is a homotropic allosteric regulator of hemoglobin.
Heterotropic Effector
An allosteric regulator molecule that is DIFFERENT from the substrate.
Phosphorylation:
Covalent modification with phosphate
Catabolism
Phosphorylated = active
Anabolism
Phosphorylated = inactive
Glycosylation
Covalent modification with carbohydrate
Zymogens:
Precursor to an enzyme. Secreted in an inactive form and are activated by cleavage.
