Enzymes 1 Flashcards
Properties of an enzyme (3)
- globular protein
- biological catalyst
- decrease activation energy
what is a co-factor?
non-protein part of the enzyme needed for activity
without them, proteins will not be able to carry out their functions and will unfold
In what 2 enzymes, are co-factors Fe2+ and Fe3+ found in?
- catalase
- peroxidase
In what enzyme is the co factor K+ found in?
pyruvate kinase
In what enzyme is the co-factor Mg2+ found in?
Glucose-6-phosphatase
what is a co-enzyme?
complex organic molecule, usually produced from a vitamin (most vitamins in our diet produce enzymes) and help enzymes by acting as a “helper molecule”
What is the co-enzyme for the vitamin derivative, riboflavin?
FAD
what is the co-enzyme for the vitamin derivative, niacin?
NAD+
what is the co-enzyme for the vitamin derivative, pantothenate?
Coenzyme A
what is a prosthetic group?
co-factor covalently bound to the enzyme, crucial for enzyme’s function (non-protein component) which is physically linked to an amino acid in a protein
what is an apoenzyme?
the inactive enzyme which needs the co-factor to activate it
what is a holoenzyme?
“whole enzyme” (the apoenzyme PLUS the co-factor)
what do oxidoreductases do?
transfer electrons
what do transferases do?
group transfers
what do hydrolases do?
hydrolysis (transfer chemical groups of water)
what do lyases do?
form or add groups to double bonds
what do isomerases do?
transfer groups within molecules (forms isomers)
what do ligases do?
formation of C-C, C-S, C-O and C-N bonds coupled to cleavage, forms covalent linkages between molecules
do enzymes affect the equilibrium?
No effect
do enzymes make a non-spontaneous reaction spontaneous?
no
do enzymes increase the rate of a spontaneous reaction?
yes
what delta G value will spontaneous reactions have?
negative (increase in entropy and decrease in enthalpy)
what is energy barrier?
energy required to position chemical groups correctly (rearrange bonds)
In a reaction coordinate diagram, what do transition states show?
the moment the chemical bonds are made and broken
does the enzyme become part of the product?
No, the enzyme remains separate from the reaction
what delta G value is needed for a reaction to happen?
Positive Delta G (energy input needed)
when does catalysis happen?
when active site is complementary to transition state
when is the point when activation energy is significantly lowered?
when substrate fits into the active site AND changes its shape. (both enzyme and substrate must change shape)
what are the 3 factors which cause the enzyme to reduce the activation energy?
- entropy reduction (reducing disorder)
- desolvation (getting rid of water by replacing substrate-aqueous bonds with substrate-enzyme bonds)
- induced fit (conformation change occurs in enzyme)
what are the 3 techniques which can be used to analyse an enzyme?
- enzyme kinetics
- mutagenesis
- 3D structure
what will happen to the initial rate of reaction if the substrate concentration is increased?
higher initial rate of reaction
when can initial velocity (v0) be calculated?
if we have excess substrate (initial substrate conc. doesn’t change)
what is Vmax?
maximum reaction velocity (reaction can’t proceed faster)
what does the Michaelis-Menten equation represent? (calculates initial velocity)
- proposed model to account for hyperoblic curve when you plot V0 ( initial velocity) over substrate concentration
- describes how reaction velocity varies with substrate concentration
what does the first part of the M-M equation form and what type of reaction is it?
ES (enzyme/substrate complex) ; reversible reaction
what does the second part of the M-M equation form and what type of reaction is it?
E + P ( enzyme and product made) reversible and slow
what is the overall rate of reaction proportional to?
the amount of ES (enzyme/substrate complex)
More ES would cause what to the rate of reaction?
it would increase rate of reaction ( and vice versa)
what is the steady state?
when rate of formation of ES= rate of breakdown of ES
synthesis rate=degradation rate
what is the rate limiting step of an enzymatic reaction?
breakdown of the ES complex to give free enzyme and product (since the more ES complex there is, the faster the second part of the reaction)
what is the definition of Km (Michaelis constant)?
Km is the equivalent to the substrate concentration at which the initial reaction rate/velocity is half of the maximum reaction rate (1/2 Vmax)
what is the better way of experimentally defining Vmax and Km?
drawing a Lineweaver- Burk plot (using the same data that was used to draw the M-M hyperbolic curve)
what does Lineweaver-Burk plot show?
determines whether Vmax has been achieved, determine the Km and mechanism for enzyme inhibitors ( a straight line is obtained)
what does a larger Km imply about ES complex?
less stable ES complex, less affinity between enzyme and substrate (bad affinity)
what does a smaller Km imply about ES complex?
more stable ES complex, more affinity between enzyme and substrate (good affinity)
the higher the Vmax, the higher the…
rate of enzyme ( faster the enzyme) and vice versa
