Transcript Enzymes - Madison Public Schools

Enzymes
Unit 3: Bioenergetics
Honors Biology
Monkemeier
Lowering Activation Energy!
 Catalysts in living systems, lower the
activation energy to speed up chemical
reactions.
 The agents that carry out most of the
catalysis in living organisms are called
enzymes.
 The chemical reactions within living
systems are regulated by controlling the
points at which catalysis takes place.
RNA?
 Most enzymes are proteins, although
increasing evidence indicates that
some enzymes are actually RNA
molecules!
 In 1981, Thomas Cech at the
University of Colorado reported that
reactions involving RNA molecules
appear to be catalyzed by RNA itself.
 RNA catalysts are called RIBOZYMES!
Ribozymes!
 Research has revealed at least two
kinds of Ribozymes.
 Intramolecular catalysis: Ribozymes
that have folded structures that
catalyze reactions on themselves.
 Intermolecular catalysis: Ribozymes
that act on other molecules without
being changesd themselves.
CONNECTING CONCEPTS!
 The ability of RNA to act as a catalyst
appears to provide a potential answer
to the question – Which came first,
the protein or the nucleic acid?
 It now seems at least possible that
RNA may have evolved first and may
have catalyzed the formation of the
first proteins!
Enzymes (as Proteins)
 The unique three-dimensional shape of an
enzyme enables it to stabilize a temporary
association between substrates.
 The area on the enzyme that matches the
shape of its substrate(s) is known as the
ACTIVE SITE.
 By bringing two molecules together in the
correct orientation, or by stressing
particular chemical bonds of a substrate,
the enzyme lowers the activation energy.
Enzyme – Substrate Complex
Induced Fit- enzyme changes shape
slightly to accommodate or match
shape of substrate.
Multi-enzyme Complexes
 Often several enzymes catalyzing different
steps of a sequence of reactions are
associated with one another in noncovalently bonded assemblies called
multienzyme-complexes.
 An example of a multi-enzyme complex is
the bacterial pyruvate dehydrogenase
multienzyme complex.
 This assembly of enzymes in bacteria is
involved with cellular respiration.
Benefits of Multienzyme Complexes
They increase catalytic efficiency by
 In a series of sequential reactions, it makes
it easier for the product of one reaction to
become the reactant of the next reaction.
 Since the reactant never leaves the
complex, it eliminates unwanted side
reactions and keeps the needed chain of
reactions moving in one direction.
 All reactions that take place within the
multienzyme complex can be controlled as
a unit.
Environmental Factors that Affect
Enzyme Function
 Every enzyme has its own SPECIFIC
range of temperature and pH at
which it will perform at its maximum
activity level.
 Temperatures and pH outside the
optimum range for an enzyme can
denature or change the shape of the
enzyme thereby altering its activity
level.
Optimum Temperature and pH
Ranges
Inhibitors
 A substance that binds to an enzyme and
decreases its activity is called an inhibitor.
 There are two kinds of inhibitors:
 Competitive Inhibitors bind to the active site
and do not allow the substrate to bind.
 Noncompetitive Inhibitors bind to a site on
the enzyme known as the allosteric site. The
binding of the inhibitor to the allosteric site
causes the enzyme to change shape and
renders it inactive
Inhibitors: Competitive and
Noncompetitive
Allosteric Site
 A substance that binds to the
allosteric site and reduces enzyme
activity is known as an allosteric
inhibitor.
 A substance that binds to the
allosteric site and increases enzyme
activity is known as an allosteric
activator.
Cofactors
 Enzyme function is often assisted by
additional chemical components known as
cofactors.
 These can be metal ions that are often
found in the active site participating in
catalysis.
 Cofactors are different from coenzymes.
Coenzymes are typically vitamins that act
with the enzyme to perfom the catalysis.
Cofactors, Coenzymes, etc
Enzymes and Metabolism
 The sum of all chemical reactions in a
cell constitutes its metabolism.
 This is usually arranged in pathways
where sequential reactions either
build up increasing complex
molecules or break down complex
molecules in steps.
 These pathways are regulated and
controlled by enzymes.