Cofactors and Inhibitors
Looking at enzymes more closely
Cofactors
•  Nonprotein helpers that help catalyze
reactions
•  Can either bind loosely or permanently
on the substrate
•  If the cofactor is organic, it is considered
a coenzyme
Vitamins are coenzymes
Vitamins are coenzymes
Scurvy
Vitamin C (Ascorbic Acid) Assists in the development of
Healthy immune system
Folic Acid - assist in the development of
spinal cord during embryonic stage
Spinal bifida
Vitamin D- helps the
absorption of calcium in
blood, and production of
phagocytes
Rickets disease
Enzyme Inhibitors
•  Selectively inhibits activity of certain
enzymes
•  Can have a permanent effect on the
enzyme, and can be irreversible.
•  There are two types: competitive and
non-competitive
Competitive Inhibitors
•  Resembles much like the substrates
•  Blocks substrates from binding to active
sites of enzymes
•  How do you think you can reverse this?
Take an enzyme supplement
Noncompetitive Inhibitors
•  Impede enzymatic reactions by binding
on a part of the enzyme
•  Causes enzyme to change shape.
•  How does this affect catalytic reactions?
It can slow down, or won’t happen at all
because the enzymes are denatured.
Example of
noncompetitive inhibitor
•  Sarin, a nerve gas
Serine, found on the active site
of acetylcholinesterase, an
enzyme of the nervous system
Example 2 of
noncompetitive inhibitor
Penicillin
Development of penicillinase
DD-transpeptidase
Homework Today:
Let’s Review
Respond to the following question using the notes you took in class:
Enzymes that work inside cells are sometimes affected by noncompetitive inhibitors. Explain how a non-competitive inhibitor affects
the activity of an enzyme.
If the inhibitor attaches to the enzyme the enzyme will change shape
making it denatured and so the reaction will not occur. And example of
a non competitive inhibitor is Sarin. Sarin is a nerve gas and if inhaled
in large amounts, can be deadly. Sarin paralizes your muscles making
it impossible for breathing, and you brain won’t be able to send
messages to your heart to pump blood.
DDT as a
noncompetitive inhibitor
Do Now (Not Later)
•  Pick up today’s handout at the front of
the room
•  Copy homework due Thursday: Study
for Exam on Thursday
•  Note in Schedule: ALL IB Bio Classes
for NEXT Thursday (12/10) report to
see Group 4 Presentations – you will be
accountable for an assignment on it
afterwards.
•  This is when a protein’s function at one
site is affected by the binding of a
regulatory molecule.
An enzyme prone to allosteric regulation has 2 or
more protein subunits
Each subunit has an active site
If one unit changes, everything else does too
Active Form
This type of enzyme oscillates between 2 different shapes,
depending on what types of ligand that binds to it
These ligands are usually
ATP or ADP molecules
Non-Active form
This type of enzyme oscillates between 2 different shapes,
depending on what types of ligand that binds to it
Ligand Regulator
Enzyme
Substrate
The ligand can stimulate
catalytic activity in the enzyme
by binding to the substrate,
which forces the enzyme to activate
through induction.
Hemoglobin functions
through cooperativity
Oxygen binding on just
one subunit can increase
the infinity to oxygen for
all other subunits.
This is why there are more
hemoglobin in areas of the
body where respiration is
needed most
•  Allosteric regulation makes sure that our body
does not produce too much of one thing.
•  How it works: the product itself attaches to
the first enzyme in the chain and inhibits the
chain of reactions until they need to produce
more of that product.
•  Noncompetitive inhibition can be positive or
negative depending on the type of ligands
(ex: external ligands vs. internal ligands).
Homework Assignment
•  Complete both worksheets. Use today’s and
yesterday’s notes to help you, as well as
pages in the textbook.
•  Bring materials for your enzyme lab
tomorrow.
•  If there is a snow day tomorrow, homework
will be due on Thursday. Check your email for
any class updates.
When you have finished copying down homework,
put everything away. We need to talk about something
serious.