ENZYME ACTION!!!
What are Enzymes?
• An enzyme is a biological catalyst. It
speeds up a chemical reaction without
being used up in the reaction or becoming
part of the products.
• All enzymes are proteins with a very
specific 3-D shape.
• A substrate is the molecule that the
enzyme acts upon. The 3-D shape of the
enzyme fits a substrate molecule like a
lock and key – a perfect fit.
Induced-Fit Hypothesis
• Enzymes are flexible molecules and
research shows that enzymes will often
change the shape of the active site very
slightly so that it is an even more precise
fit for the substrate.
• This phenomenon is known as the
induced-fit model of enzyme activity.
Enzyme Action
ENZYMES IN ACTION
http://www.youtube.com/watch?v=E-_r3omrnxw
Enzyme Action
Points to Remember…
• Active Site & Substrate
• Induced-fit Model
• Activation Energy
• Enzyme-Substrate Complex
• Enzymes are Like Batman!!!
(Git R Done and Git Out!)
Is That You Robin?!?!
• Enzymes may be
assisted by cofactors
and coenzymes.
• Cofactors are nonprotein groups.
• Coenzymes are
organic cofactors.
• These entities may
bind to the active site
or the substrate to
assist in enzyme
activity.
ENZYME INHIBITION
Why End a Good Thing?
• Inhibit means stop! If enzyme action is critical
to normal health, then why would we want to
stop it?
– Energy Efficiency – It requires energy to
build molecules or break them down.
– Build up of Toxins – Some products are
great until their concentration gets too high –
then they become toxic to the cell. (Too much
of a good thing!)
Enzyme Inhibition
• There are two main categories of enzyme
inhibition – competitive and noncompetitive.
• Competitive inhibition means the active site is
being competed for by another molecule that is
not the substrate.
• The enzyme can’t grab onto the substrate
because it is occupied with a noncompetitive
inhibitor that has a similar shape as the
substrate – but not the perfect shape – no work
is done.
Competitive Inhibition
Noncompetitive Inhibition
• Noncompetitive inhibition occurs when an
inhibitor molecule binds to the enzyme at a
site other than the active site.
• This binding of the inhibitor changes the
3-D shape of the active site and renders it
useless.
Allosteric Regulation
• Allosteric regulation is a form of noncompetitive
inhibition.
• Allosteric sites on the enzyme are used by
regulatory molecules to binds to in order to
control enzyme action.
• Inhibition – Inhibitor binds to allosteric site to
stabilize inactive form of enzyme – active site
not right!
• Activation – Activator binds to allosteric site and
stabilizes the working form of the enzyme –
active site is just right!
Allosteric Regulation
ALLOSTERIC REGULATION
http://www.youtube.com/watch?v=d5fDEUhjo-M
FEEDBACK INHIBITION
• Feedback inhibition occurs when there is a chain
of reactions that must occur in order to achieve a
final product.
• When enough product has been made, some of
the surplus product goes back to an enzyme
earlier in the chain and inhibits it.
• When the surplus product is used up by the cell
– the product acting as an inhibitor will be
consumed and open the pathway again.
FEEDBACK INHIBITION
FEEDBACK INHIBITION
http://www.youtube.com/watch?v=DHZtOKyMPRY
FIN