Lecture 9 - Enzyme kinetics Flashcards
example of enzymes being stereospecific
usually glucose switches from its aldehyde state to alpha and beta usually
but during synthesis of cellulose, only B form is selected for by enzyme
what is delta G’º
diff between the substrates and products (ratio of S to P
- if it’s negative, then product is favoured as energy is released
- never affected by enzyme
what is delta G‡
activation energy
determines reaction rate
energy needed to get to TS‡
what is TS‡
transition state of the reaction
can only be reached with activation energy
what is the active site most complementary to
for transition state
which allows transition state stabilisation
what is the proximity effect
enzyme bringing together subsrtaetes and makes them more liekly to react
what are the 2 ways the AAs in the active site can influence catalysis
- bind via non-covalent interactions with the substrate
- some AAs have catalytic functional groups
e.g. - ionisible side chains - groups that can form covalent bonds to the substrate (nucleophiles/electrophiles)
or - metals (cofactor)
what are the 2 types of enzyme cofactors
- metal ions (loose bound or tightly bound - metalloezymes)
- coenzymes (transient carriers of atoms/functional groups)
2 types of coenzymes
- cosubstrates = loosely bound, recycled (e.g. ATP, coA)
- prosthetic groups = coenzyme is tightly bound to enzyme (e.g. haem)
what is the rate equation for enzymes
Δ[P] / Δ t = v = k[S]
v being velocity/rate of reaction
k is a rate constant specific to reaction
what is first order
linear direct correlation
so V0 = k[S]
what is zero order
when enzyme added
and it gets to a point conc of substrate doesnt matter
since all active sites are occupied
what is the fastest step in two step enzyme reaction scheme
E + S <-> ES
fast and reversible
what is the slowest step in two step enzyme reaction scheme
ES -> E + P
ie the catalytic step
what is kcat
the catalytic constant
only at when enzymes are fully saturated
for simple reactions it’s = to k2
kcat=vmax/[Et]
what is the specificity constant
kcat/km
can measure both kcat and km and then calculate using that equation
and it can be used to compare diff enzymes
(higher the result=the better the enzyme
oxidoreductases
aka dehydrogenases
catalyse redox reactions
transferases
catalyze group transfer reactions
hydrolases
catalyse hydrolysis reactions
so it’ll cleave a bond and add water to the products
lyases
catalyse lysis
cleave off a group leaving a double bond
(NOT a redox reaction or hydrolysis)
e.g. decarboxylases, aldolases, dehydratases
some will do the reverse reaction (adding to a double bond) = synthases
isomerases
caltalyse isomerism reactions
no change in molecular formula
only changes the structure
ligases
catalyse joining of two substrates
forming new covalet bond
unlike these, needs chemical energy e.g. ATP
