Enzyme Properties, Kinetics and Regulation Flashcards
What are Enzymes?
They are biological catalysts that speed up reactions without altering the final equilibrium and they aren’t used up
Substrate Specificity?
Allows enzymes to only catalyse one type of reaction which is usually determined by the active
Oxidoreductases?
Add O2 or remove H2 (Lactate Dehydrogenase)
Transferases?
Transfer of functional group within the same molecule (Amino transferase)
Hydrolases?
Cleaves bond by addition of water (Trypsin)
Lyases?
Breaks the bond between a carbon atom and another atom
Isomerases?
Isomerisation reactions (Isomerase)
Ligases?
Uses ATP to catalyse the formation of new covalent bonds (DNA ligase)
What stabilises proteins?
H-bonds, electrostatic salt links and hydrophobic actions
Induced fit model?
a change in shape of he enzyme when substrate binds to active site
Michaelis Menton Equation?
Km = K2 + K-1 / K1 K1 = Enzyme substrate forming K-1/K2 = Getting rid of ES
Determining Initial Velocity?
When [S] «_space;Km, rate depends linearly on [S], so [S] is rate limiting
When [S]»_space; Km, rate is independant of [S], [E] is rate limiting
Rate (v) is kinetically dependant on [E] total at any given value of [S]
Limiting velocity?
Vmax = K2 [E]total is the limiting velocity of the reaction at any given concentration
Obtained at saturating levels of substrate
Referred to as the maximum velocity
Michaelis Constant?
When [S] = Km, V = 1/2 Vmax, so Km is the substrate concentration at half the limiting velocity
Km is a measure of the lifetime of the ES complex and indicates concentration required for significant catalysis to take place
Kcat = Vmax/[E]total and Ka = Kcat/Km
Types of Inhibitors?
Reversible inhibitors - bind to enzyme and can dissociate
Irreversible inhibitors - bind permanently
Competitive, non-competitive and incompetitive inhibitors?
Competitive bind directly to active site
Non-Competitive bind away from site altering enzyme shape
Incompetitive - Only binds to E-S complexes to stop product from forming
Inhibitors effect on Km and Vmax?
Competitive inhibitors increase Km and dont effect Vmax. it can be overcome by increasing [S] as when [S]»_space; Km, the rate is independent of Km
Non-Competitive reduces Vmax but Km is not affected. Inhibition is independent of [S] as rate always depends on Vmax
What is allosteric regulation?
Where a molecule binds to an enzyme someplace other than the active site (allosteric site)
Allosteric Enzymes?
They have multiple active sites and when an inhibitor binds, all active sites are changed slightly so they dont work as well. Allosteric activators can cause an increase in function.
What are Modulators?
They change enzyme structure making the enzyme either less or more active (T or R state)
What is feedback inhibiton?
A sequence of enzymes produce a product which inhibits initial enzymes used to start the reaction
