Enzymes Flashcards
2 sites on the active site
binding site
catalytic site - reduce chemical activation energy
forces involved in binding
h bonds, hydrophobic interactions, van Der Waals, electrostatic, reversible covalent
what determines substrate specificity
side chains
allosteric sites
different from active site
binding = conformational change = change in rate of reaction
regulation
co factors
help enzyme catalyse reaction
transferases
transfer functional group from substrate to substrate
hydrolases
hydrolysis of substrate
lyases
adding or removing group to form double bond
isomerases
transfer groups within molecules
ligases
bond formation coupled with atp hydrolysis
transition state
transient molecular state that is no longer substrate or product
2 types of enzyme reaction
exergonic - spontaneous (produced more energy than input
endergonic - unfavourable (require more energy than it yields)
factors involved in enzyme catalysis
R groups
chemical complementarity
microenvironment
orientation
hydrophobic interactions
ionic bonds
h bonds
transient covalent
van der Waals
4 catalytic mechanisms
metal ion catalysis (involves metal ion cofactor)
catalysis by approximation (bring reactants closer)
covalent catalysis (share e-)
acid-base catalysis (adding either speeds up)
rate of reaction is called
velocity (V0) (amount of S covered to P per time)
unit for V0
micro mol / min
is substrate doubles V0…
doubles
if enzyme saturation occurs V0…
plateaus
rate of reactions depend o dissociation of …
product from enzyme
if enzyme doubles, V0…
doubles
Vmax
max rate of reaction
Km
substrate conc at half Vmax
(measure of enzyme affinity for substrate)
low Km =
high affinity for substrate
strong binding
greater V0
faster rate of reaction.
enzyme assays
monitors disappearance of substrate or appearance of product
measurements of enzyme assays
colour
high absorbance / fluorescence
chromatography
radiography
substrate analogues
chemical compound that is similar in structure to substrate
reversible inhibition
bind by weak covalent but don’t change shape chemically
competitive inhibitor effect on Vmax, half Vmax and Km
Vmax unchanged
Km increases - rate is reduced and affinity of enzyme reduces
half Vmax unchanged
non competitive inhibitor effect on Vmax, half Vmax and Km
Vmax reduced
Km unchanged
half Vmax reduced
uncompetitive inhibition
binds only to enzyme substrate complex
all 3 reduce
regulation of glycolysis (hexokinase)
allosterically inhibited by G-6-P
allosteric enzymes features
multi subunit (active site on each subunit = oligomeric)
cooperatively (binding = conformational change = increase affinity)
regulated via allosteric sites
allosteric enzyme graph
sigmoidal curve (rapid increase in enzyme velocity)
narrow range of s
sensitive to small changes in s
reversible covalent modification
adding or taking Pi changes tertiary structure and alters catalytic activity eg
protein kinases - phosphorylates
protein phosphatases - dephosphorylates
proteolytic activation
when hydrolysed they are active (irreversible hydrolysis of one or more peptide bond)
other methods of regulation
gene expression
breakdown as short half life
