Enzymes Flashcards
enzymes are ….. proteins
globular
ribozymes
catalytic RNA molecules with no protein component
apoenzymes
protein component
holoenzymes
whole enzyme
active site
where the substrate binds
enzyme functions
lower activation energy
increase rate of spontaneous reactions
addition of an enzymes lower the
activation energy
delta G =
Delta H - T delta S
enzymes form non-covalent bonds with substrate molecules called the
binding energy
binding energy allows the enzymes to
take the reaction through a different path of reaction intermediates
how do enzymes reduce the activation energy?
entropy reduction
desolvation
induced fit
desolvation
weak bonds between substrate and enzymes replaced with H bonds
Vo
initial velocity
low substrate concentration gives you an
increase in Vo
when [S] becomes so large that Vo changes are vanishingly small you get
maximum reaction velocity
Vmax
E + (K1) gives ES which gives
E + P (k2)
K1 is a ……….. reaction
reversible
K2 occurs ………. than K1
slower
Study of initial rates of reaction are termed
steady state kinetics
Rate limiting step of enzymatic reactions is the breakdown of
ES complex to give free enzymes and product
Half of Vmax is
michealis constant
the substrate concentration at which the initial reaction rate is half of the maximum reaction rate
Km
the ratio of rate constant for breakdown of ES to E + S compared to the rate constant for formation of ES from E + S
Km
Larger Km indicates a
less stable ES complex
Smaller Km indicates a
more stable ES complex
Km indicates the ……. for a substrate
affinity
Glucose + ATP =
glucose-6-phosphate + ADP
Glucokinase and hexokinase catalyse
glucose to glucose 6 phosphate
Glucokinase Km and Vmax are both
high
Hexokinase Km and Vmax are both
low
what increases after a meal
glucokinase
when blood glucose is low - it is released from the liver via
gluconeogenesis
when blood sugar levels are low
Glucokinase also low
isoenzymes
different enzymes that catalyse the same reaction
hexokinase is in
muscle
Glucokinase is in the
liver
electrophoresis is useful to
separate plasma protein
elevation of CK2 indicates
myocardial infarction
Catalysing reaction with two or more substrates usually involved
transfer of groups from one substrate to the other
In an ordered sequential reaction mechanism the enzyme exists in a ………….. structure
ternary
Lactate dehydrogenase catalyses
pyruvate to lactate
co enzyme needed: NADH
example of random sequential mechanism
phosphocreatine from creatine
Allosteric enzymes are made up of
many subunits, which contain many active sites
3 things that can change the way an enzyme functions
temperature
pH
inhibitors
feedback inhibition
build up at the end product of a pathway can slow the entire pathway
allosteric effectors bind to a site that is not the ……….. which changes the enzymes structure
active site
allosteric enzymes
concerted model
each subunit exists in two different conformations
one binds substrate and the other doesn’t
allosteric enzymes
sequential model
no flipping between conformation sites
substrate binding causes a change in ONE subunit
Different ways inhibitors can effect enzymes
Competitive inhibitor
Non-competitive inhibitor
Irreversible inhibitor
Feedback inhibition
Proproteins can be cleaved to give active enzyme by
proteases
