a catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction an...
TRANSCRIPT
A catalyst Is a chemical agent that speeds up a
reaction without being consumed by the reaction
An enzyme is an organic catalyst Enzymes are proteins
Enzyme
Substrate(Reactants)
Allosteric Site
Active Site
Activator or Inhibitor
Enzymes can only work with certain substrates
The shape of the enzyme must match the shape of its substrate- The root of the enzyme’s name typically indicates the substrate which it acts upon e.g. ATPase, Amylase, Sucrase
When the substrate binds to the active site, the enzyme changes conformation (shape) to make a better fit.
Figure 8.16 (b)
Enzyme- substratecomplex
Figure 8.16
Substate
Active site
Enzyme
(a)
Sucrase
Sucrose + Sucrase Glucose + Fructose + Sucrase
http://www.youtube.com/watch?v=eMuyKN_VW3k
• The initial amount of energy needed to start a chemical reaction
The energy required to get the reactants ready to react
Fre
e en
ergy
Progress of the reaction
EA
Figure 8.14
A B
C D
Reactants
A
C D
B
Transition state
A B
C D
Products
activation energy EA
Enzymes lower the activation energy
How? Orienting substrates
correctly Putting stress on
substrate bonds Providing a
favorable environment
This increases the rate of the reaction.
Progress of the reaction
Products
Course of reaction without enzyme
Reactants
Course of reaction with enzyme
EA
withoutenzyme EA with
enzymeis lower
Fre
e en
ergy
Figure 8.15
http://www.youtube.com/watch?v=Dd1yi2aVoOc
(1) Increase the number of substrate molecules in solution (increase conc’n)
(2) Increase the number of enzymes in solution (increase conc’n)
(3) Increase the temperature of the solution (up to a certain point)
A reaction is said to be “saturated” when 100% of enzymes have their active sites filled with substrate.
Vmax is maximum velocity (speed) of rxn
If there are left-over reactants (substrates), then you could add more enzymes.
If there are no more left-over reactants (substrates), then adding more enzymes will not increase the rate.
Change the pH so it is above or below its optimal value.
This changes the enzyme’s conformation (shape) causing it to become dysfunctional
E.g. Add H2SO4(aq) (Sulfuric Acid)
Above a certain temperature, enzymes’ activity starts to decline because the enzyme begins to denature (unravel)
Reactions occur in a sequence and specific enzymes catalyze each step
Z U
V
WX
Y
(a) Z + Y U U V W W X + Y
(b) Initial Reactant: Z End product: E (desired product)
Figure 8.19 (b) Competitive inhibition
A competitiveinhibitor mimics the
substrate, competingfor the active site.
Competitiveinhibitor
A substrate canbind normally to the
active site of anenzyme.
Substrate
Active site
Enzyme
(a) Normal binding
Figure 8.19
A noncompetitiveinhibitor binds to the
enzyme away fromthe active site, altering
the conformation ofthe enzyme so that its
active site no longerfunctions.
Noncompetitive inhibitor
(c) Noncompetitive inhibition
When one activator or inhibitor bind to an allosteric site, it will have an effect on all the subunits of an enzyme
Stabilized inactiveform
Allosteric activaterstabilizes active fromAllosteric enyzme
with four subunitsActive site
(one of four)
Regulatorysite (oneof four)
Active formActivator
Stabilized active form
Allosteric activaterstabilizes active form
InhibitorInactive formNon-functionalactivesite
(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again.
Oscillation
Figure 8.20
http://www.youtube.com/watch?v=d5fDEUhjo-M
• The end product of a metabolic pathway shuts down the pathway
Active siteavailable
Isoleucineused up bycell
Feedbackinhibition
Isoleucine binds to allosteric site
Active site of enzyme 1 no longer binds threonine;pathway is switched off
Initial substrate(threonine)
Threoninein active site
Enzyme 1(threoninedeaminase)
Intermediate A
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
End product(isoleucine)
Figure 8.21
http://www.youtube.com/watch?v=c8FcZVJS1Q8