Enzymes Flashcards
enzymes convert what to products while remaining unchanged themselves?
substrates
what are enzymes?
catalysts that convert substrates to product while remaining unchanged themselves
what are reacts in enzymes called
substrates
Name an enzyme that isnt a protein
RNA
What are the 4 main advantages of biocatalysis over inorganic catalysts?
- Greater reaction specificity, so avoids side products
- milder reaction conditions
- higher reaction rates
- capacity for regulation
how are enzymes classified?
on the types of reactions that they catalyse
what does lyases do
group elimination to form double bonds
what do ligases do
bond formation coupled with ATP hydrolysis
what does bromelain do
an enzyme that facilitates hydrolysis of proteins
Proteolytic enzymes do what
catalyse the hydrolysis of peptide bonds
what type of enzymes illustrate the range of enzyme specificity
proteolytic enzymes
enzymes do not alter what
The deltaG of a reaction
Free energy is what
measure of energy capable of doing work
Change in free energy when a reaction occurs is symbolised by what
DeltaG
The more exergonic a reaction, the larger or smaller the equilibrium constant will be?
Larger
The more endergonic a reaction, the larger or smaller the equilibrium constant will be?
Smaller
the equilibrium constant is directly proportional to what?
To DeltaG
Is deltaG positive or negative for an endergonic reaction?
Positive
association rate is what?
association rate constant x concA x ConcB
dissociation rate is what
dissociation rate constant x ConcAB
At equilibrium, what is the relationship between association rate and dissociation rate?
Association rate = Dissociation rate
enzymes increase reaction rates by decreasing what
Activation energy
what is a transition state
A molecular form that is no longer substrate but not yet product
What is the activation energy
the energy required to form the transition state from the substrate
Where does catalysis take place on the enzyme
Active site
How do enzymes catalyse reactions in terms of transition states
They stabilise transition states
Enzymes bring substrates together to form what at the active site?
form an enzyme-substrate complex at the active site
What promotes the formation of the transition state?
Interaction of the enzyme and substrates at the active site
What is the specificity of the an enzyme due to
To the precise interaction of the substrate with the enzyme
The active site is what and formed by what
is 3D cleft formed by groups that come from different parts of the amino acid sequence
how are substrates bound to enzymes (what bonds)
multiple weak noncovalent interactions
specificity of binding is defined by what
3D structures of the active sites and substrates
what is excluded from the active site unless it is a reactant?
water
What character enhances the binding of the substrate as well as catalysis?
Non polar character
what are the 2 models for the interaction of enzymes with their substrates
Lock and Key
Induced Fit Model
Hexokinase undergoes what on substrate binding
Induced fit
What is the energy released upon interaction of the enzyme and substrate?
Binding energy is the free energy released
When is binding energy the greatest?
When the enzyme interacts with the transition state, facilitating the formation of the transition state
Binding energy is a major source of free energy used by enzymes to do what
lower activation energies of reaction
Enzymes being binded to transition states best was proposed by who
Linus Pauling 1946
Enzyme active sites are what to the transition state of the reaction?
complementary
Enzymes bind what better than substrates
Transition state
Describe the binding energy in terms of the stickase exampel
Free energy required to draw the stack into the bent shape is offset or paid for by interactions between E and S in the transition state
What are inhibitors of enzymes
transition state analogs
Racemization of proline goes through a transition state in which the alpha carbon is what
trigonal
Pyrrole 2 carboxylic acid had what geometry
Trigonal
The similarity between pyrrole 2 carboxylic acid and racemization of proline means that pyrrole 2 carboxylic acid is what
Transition state analog and a potent inhibitor of proline racemase
Summary of enzymes
- Reactions will proceed only if the free energy difference between reactant (substrate) and product is negative, however the rate may be very slow due to large activation energy required to reach the Transition state.
- Enzymes lower the activation energy by providing an alternative pathway for the reaction to proceed.
- Enzymes affect the rate of reaction but not the equilibrium position. They catalyse the forward as well as the reverse reaction
- Enzymes are not altered in the reaction and can be re-used
- Enzymes stabilise the transition state. Binding energy offsets the activation energy.
- Enzymes differ from other catalysts in that they are specific for the substrate. They also work at much milder conditions (pH 7 and 370C)
