enzymes Flashcards
(36 cards)
what is the general role of enzymes
to catalyse biological reactions by lowering the activation energy
what does delta G have to do with reactions
-ve delta g means the reaction will occur spontaneously
+ve delta g means the reaction will occur non spontaneously
do enzymes alter the equilibrium of a reaction?
they do not alter their equilibrium concentrations
what are the 6 major classes of enzymes
1) oxoreductase
2) transferase
3) hydrolase
4) lyase
5) isomerase
6) ligase
what is a cofactor (2 classes) and what is its purpose
metal ions and co enzymes
these are other non protein factors that help to catalyse reactions
how do metal ions act as a co-factors
they act as lewis acids ( electon accepting) and can participate in acid base catalysis.
they form coordination compounds with precise geometrics, good for positioning reactants exactly where they’re needed.
how do co-enzymes act as co-factors?
They’re small organic molecules, they work as carriers ( atoms,electrons, functional groups etc)
what is reaction coupling and how do enzymes mediate this
enzymes couple spontaneous reactions to non spontaneous ones, overall making delta G -ve = a spontaneous reaction.
what are 3 features of an enzymes active site
they have amino acid side chains projecting into it
they bind substrates via multiple weak interactions
these determine the specificity of the reaction
what are the 4 types of enzyme substrate bonds and what is a feature of the bond
ionic- non covalent bonds with charged side chains
hydrogen bonds- useful for specific geometry, side chaisn or backbone often act as H+ bond donors/acceptors
van der waals- weakest of the bonds. Between protein and substrate atoms in close proximity
covalent bonds- rare bonds, much stronger. only occur if you can reverse to original state.
what does the induced fit model demonstrate
that enzymes are dynamic, active site side chains can be subtly rearranged to create a network of H+ bonds at the active site to best fit the substrate
what is covalent catalysis
a reactive, short lived intermediate that is covalently attatched to the enzyme.
what type of amino acids are likely to be involved in acid base catalysis
glu, asp- positively charged
lys- arg- negatively charged
histidine particularly suitable as its pKa is close to physiological PH so it doesn’t take much to make it a proton donor or acceptor.
What is expected to bind tightest to an enzyme: the substrate, product or transition state?
should bind more tightly to transition state then the substrate.
how is the progression of a reaction through the tranisiton state affected by the presence of an enzyme
what are the two models used to describe enzyme- substrate binding
lock and key model- enzyme and substrate fit perfectly into eachother
induced fit model- simular but small changed are made to induce the fit once they join together,
how is activation energy lowered?
1)ground state destabilisation- dont want the enzyme substrate complex to be too comfortable that it doesnt want to react
2)transition state stabilisation- by reducing the activation energy the transition state becomes more energetically favourable
3) Alternative reaction pathway- different energy transition states.
what are the three main catalytic pathways that enzymes are involved in?
proximity and orientation effects, preferential binding of transition state, acid- base catalysis
when there is an excess of substrate, reaction velocity is _______ to enzyme concentration
proportional
what does the Y intercept represent on a lineweaver- burk plot?
1/Vmax
what does the X intercept represent on a lineweaver- burk plot?
-1/ Km
what is the significance of Km
it tells us how well the enzyme grabs the substrate
it measured by the substrate needed to reach 1/2 of Vmax.
what does a high or a low Km tell us
high= the enzyme has a low affinity for the substrate
low= the enzyme has a high affinity for the substrate
if an enzyme has multiple substrates, how can we use Km to determine substrate preference?
The lower the Km value the more preference the enzyme has for that particular substrate.
