Enzymes Flashcards
Apoenzyme
an enzyme without a cofactor
Holoenzyme
complete catalytically active enzyme
Cofactors
small organic molecule derived from vitamins and called coenzymes and metals.
Metals
tightly bound coenzymes are called prosthetic groups
Free energy
the measure of useful energy
When can a reaction take place spontaneously?
only if G is negative
When can this reaction NOT take place spontaneously?
only if g is positive
The amino acid position is in the N-terminus
acetylation
The amino acid position is in the C-terminus
Amidation
Ser, Tyr
phosphorylation
Pro
hydroxylation
Tyr,Lys
Methylation
Ser, Thr
Palmitaylation
Ser, Thr, Tyr
Sulphination
What is the heart of enzyme catalysis
the stabilization of the transition state
What are some characteristics of an active site?
1) There is a 3-D Cleft
2) Small part of the total volume of the enzyme
3) Unique micro environment
4) Substrates bound to enzymes by multiple weak attractions
5) Binding specificity depends on precisely defined arrangements
Induced Fit Theory
Daniel Koshland Jr. states that the active sites of some enzymes assume shape that is complementary to substrate after substrate binds
Binding Energy
The free energy that is released when weak interaction between complementary enzymes and substrates are formed.
Kinetics
study of the rates of chemical reactions- enzyme catalyzed reactions
Velocity
the quantity of the reactant A that disappears
Rate Constant
the way velocity is directly related to concentration of A by constant K
First-order reaction
where V is directly proportional to the reactant concentration
Second-order reaction
reaction with 2 reactants
Pseudo-first -order reaction
if reactant B is more than reactant A, and if A is present in low concentrations, reactions will be first order with respect to A and will not depend on B.
Michaelis -Menten Model
Initial velocity of catalysis is defined as the number of moles of product formed per unit time shortly after the reaction has begun
Vmax
when the enzyme is saturated with substrate
Km
substrate concentration at which reaction velocity is 1/2 max. volume.
lower value of Km
the tighter the substrates binding
Km can be a measure of..
the affinity of enzyme for substrate
Km values can vary
depending on environmental conditions (pH, Temp..)
Kcat/KM
measure of catalytic efficiency
Sequential
all substrates must bind to enzyme before any product released, these can be ordered or random
Double-displacement
one or more products are released before all substrates bind enzyme
Allosteric enzymes
enzymes that regulate the changes of biochemical compounds in metabolic pathways
Allosteric site
Have a 2nd regulatory site different from active site
Phosphofructokinase
one of the most important regulatory allosteric enzyme in glycolysis and composed of 4 subunits
Catalytic Strategies
- Covalent Catalysis
- Acid-Base Catalysis
- Metal- ion catalysis
- Stabilization of transition State
Metal Ion uses in catalysis
- Binding substrates in the proper orientation and there fore increasing binding energy
- may generate a nucleophile by increasing the acidity of a nearby molecule.
- electrophilic catalyst
Metalloenzymes
contain tightly bound metal ions
Metal-activated enzymes
contain loosely bound metal ions
Competitive Inhibition
resembles the substrate and binds only to the free enzyme active site-not enzyme-substrate complex
Kinetics with competitive inhibition
no effect on Vmax, but increases Km
Uncompetitive Inhibition
binds only to enzyme-substrate complex and NOt to free enzyme. Cannot be overcome by the addition of more substrate.
Kinetics with uncompetitive inhibition
decreases Vmax and decreases Km
Noncompetitive Inhibition
can bind at same time with substrate to enzyme at different binding sites and can bind free enzyme and enzyme-substrate complex. Cannot be overcome by addition of substrate
Kinetics with noncompetitive inhibition
decreases Vmax and Km does not change
