Enzyme Kinetics Flashcards
what is Vmax?
the maximum velocity of an enzymes - when it cannot work any faster
what is the Km?
the substrate concentration at Vmax over 2
what is the V a measure of?
the moles of substrate converted to product per second
the michaelis - menten is a _____ shaped graph
hyperbolic
as the Km increases the affinity of the enzyme for the substrate ____
decreases
in the MM Model what does K1 represent ?
E and S forming ES
the forward rate constant for enzyme association with the substrate
in the MM Model what does K2 represent ?
ES (binding complex) forming E and P (product)
s the forward rate constant of enzyme conversion of substrate to product (P)
in the MM Model what does K-1 represent ?
ES going back to E and S
k-1 is the backwards rate constant for enzyme dissociation from the substrate.
What is the michaelis constant equation Km?
K1
basically - dissociation over association
BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not ______ - reaction velocity never quite reaches true ______ !
BIG “BUT” - It is not straightforward to determine Vmax and KM from such a graph because the kinetics are not linear - reaction velocity never quite reaches true Vmax !
the michaelis menton equation describes the ___of catalysis as a function of _____ concentration. This describes a hyperbola
describes the rate of catalysis as a function of substrate concentration. This describes a hyperbola
what is the michaelis menton equation?
Km + [S]
what is the straight line equation?
1 = Km . 1 + 1
– —— — ——–
V Vmax [S] Vmax
in the lineweaver burk plot Vmax =
Vmax = intersection of the straight line with the Y axis
in the lineweaver burk plot Km=
KM = intersection with the X axis
the lineweaver burk plot is a _____ _____ plot
double reciprocal
A ___ KM means that an enzyme
only needs a little substrate to
work at half-maximal velocity
low
A ___ KM means that an enzyme
needs a lot of substrate to work at
half-maximal velocity
high
Enzymes can display the same ___
and have different __
Vmax and Km
a clinical examples of why Vmax and Km matter would be glucose homeostasis and _____
MODY
maturity onset diabetes of the young
both ___ and ___ catalyse the reaction of glucose + ATP —-> glucose-6-phosphate + ADP
hexokinase and glucokinase
hexokinase has a ___ Km for glucose
low
what does the ____ Km for hexokinase mean it can do?
Low KM maintains energy production in red
blood cells by glycolysis even if glucose
levels fall dramatically
where is hexokinase found?
RBCs
where is glucokinase found?
liver and pancreas
glucokinase has a ____ Km for glucose
high
what does the ___ Km for glucose mean glucokinase is able to do
high, High KM enables glucose sensing & homeostasis. It’s abundance in liver is regulated by insulin. Excess blood glucose is metabolised
what happens in MODY?
get loss of glucokinase activity and this means loss of insulin-mediated glucose homeostasis
look at slides for other clinical effetc - hypoxia and stuff
.
what is revesible competitive inhibition
Inhibitor binds to the active
(catalytic) site & blocks
substrate access.
Orthosteric Inhibition - at the same site
what is reversible non - competitive inhibition
Inhibitor binds to a site other than
the catalytic centre; inhibits enzyme
by changing its conformation.
Allosteric Inhibition - at different sites
what is irrreversible non - competitive inhibition
Inhibition cannot be reversed. Usually involves formation or breakage of
Covalent bonds in the enzyme complex
in competitive inhibition the ___ does not change but the ____ varies
vmax,
Km
what happens to the Km in competitive inhibition?
it increases
what clinical example is there of competitive inhibition in treatment
methanol poisening - ethanol has a much lower Km for Alcohol dehydrogenase than methanol meaning that ADH will go down the ethanol metabolism route rather than the methanol toute
in non-competitive inhibition the ___ varies and the __ does not change
Vmas varies and the Km does not change
Inhibition of rate limiting enzymes by ___ _____ s is a common mechanism of allosteric control
end products
______ enzymes do NOT follow Michaelis-Menten kinetics
allosteric
with allosteric enzymes increasing substrate concentration results in a ___ curve instead of a hyperbola
sigmoidal
allosteric enzymes can be ___ and ___
activators and inhibitors
what is an importnat example of allosteric regulation in the body
haemoglobin
in haemoglobin the binding of oxygen exhibitis ____ ____
positive co-operativity
what is the binding of oxygen to haemoglobin controlled by? 3 things
- H+
- CO2
- 2,3 bisphosphoglycerate
a side product of glycolysis
why does myoglobin not show co-operativity ?
it can only bind one O2 at a time
