Transcript Document

Metabolic Pathways
• A metabolic pathway begins with a specific molecule
and ends with a product
• Each step is catalyzed by a specific enzymeimportance of protein synthesis!
Enzyme 2
Enzyme 1
A
Reaction 1
Starting
molecule
© 2011 Pearson Education, Inc.
Enzyme 3
D
C
B
Reaction 2
Reaction 3
Product
METABOLISM = Catabolism + Anabolism
• Catabolic pathways release energy by breaking down
complex molecules into simpler compounds (Cellular
respiration, the breakdown of glucose in the presence of
oxygen)
• Anabolic pathways consume energy to build complex
molecules from simpler ones (synthesis of protein from
amino acids)
© 2011 Pearson Education, Inc.
Enzyme Review!
Briefly sketch 3 graphs that show the initial reaction
rates of enzyme catalyzed reactions with varying
temperature, enzyme concentration, and substrate
concentration. Label each graph, and compare the shape
of each curve.
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Enzyme Inhibitors
Enzyme Unit –Part 2
Inhibition
• Active site of enzyme fits perfectly to
substrate
• However, it is possible for another
molecule to bind to an enzymes active site
if it is very similar in shape to the enzyme’s
substrate
• This would inhibit the enzyme’s function
Substrate
Enzyme
Inhibitor
Enzyme Inhibitors
• Competitive inhibitors bind to the active site of an
enzyme, competing with the substrate
• Noncompetitive inhibitors bind to another part of
an enzyme, causing the enzyme to change shape
and making the active site less effective
• Examples of inhibitors include toxins, poisons,
pesticides, and antibiotics
• Cyanide poisoning
© 2011 Pearson Education, Inc.
Figure 8.17
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive
inhibition
Substrate
Active
site
Competitive
inhibitor
Enzyme
Noncompetitive
inhibitor
Allosteric
Competitive inhibition
• Usually reversible, because the inhibitor does not
permanently bind to the enzyme
• Inhibition can be reversed by increasing concentration of
substrate
Competitive inhibition examples
• ACE inhibitors – Block the pathway of hormone,
angiotensin II, from constricting blood vessel and
increasing blood pressure (Blood vessel dilate)
• ACE Inhibition animation
• Carbon Monoxide poisoning – CO vs. O2 with
hemoglobin
Non-competitive inhibition
• NON-COMPETITIVE Inhibition does not depend
on substrate concentration
• Inhibitor will STILL block enzyme function,
regardless of low/high concentration of
substrate
• Two main types
• Irreversible inhibition- *could be at ACTIVE
SITE!
• Allosteric inhibition
Irreversible inhibition
• Sometimes, inhibitor can remain permanently bonded with
the active site and therefore will cause an irreversible block to
the substrate
• No competition occurs because no matter how much
substrate is present (NON-COMPETITIVE) the active sites will
be permanently occupied by the inhibitor
• http://www.youtube.com/watch?v=PILzvT3spCQ
Non-competitive irreversible
inhibition
• Penicillin works by
permanently occupying the
active site of an enzyme
that is essential for the
synthesis of bacterial cell
wall.
• Penicillin and other βlactam antibiotics act by
inhibiting penicillin-binding
proteins, which normally
catalyze cross-linking of
bacterial cell walls.
Non-competitive allosteric inhibition
• If a molecule can bind to another site on the enzyme (besides
active site) and stop enzyme function, it is an allosteric
inhibitor
• Can disrupt the 3D shape of enzyme molecule so active site
cannot accept substrate
• Can be reversible
or irreversible
End-product inhibition
• As an enzyme converts substrate to product, it is slowed
down because the end product binds to another part of the
enzyme and slows down its function
• Called negative feedback inhibition
• The more product = slower reaction
• Controls metabolic processes to stop enzyme from “running wild”
Animation
End product inhibition
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Enzyme Inhibitors
Vioxx and other prescription nonsteroidal antiinflammatory drugs (NSAIDs) are potent inhibitors of the
cycloxygenase-2 (COX-2) enzyme. High substrate
concentrations reduce the efficacy of inhibition by these
drugs. These drugs are
a)
b)
c)
d)
competitive inhibitors.
noncompetitive inhibitors.
allosteric regulators.
feedback inhibitors.
Enzyme Quiz on Thurs. 4/9!
Concepts to know:
• Lock and Key hypothesis
• Induced fit hypothesis
• vocab: substrate, enzyme, active site,
activation energy
• reaction curves
• effects of temperature, and pH, enzyme
concentration, and substrate concentration
on enzyme controlled reactions
• Types of enzyme inhibition