how does cyanide work? controlling enzyme function
TRANSCRIPT
How does Cyanide work?
Controlling Enzyme Function
METABOLIC PATHWAYS So far we have looked at a single enzyme
promoting a single reaction A B
In reality, groups of enzymes catalyze multiple chemical reactions in a metabolic pathway
A B C DThe product of one reaction becomes the
immediate substrate for the next enzyme and is rapidly consumed
E1
E1 E2 E3
These pathways of enzyme-catalyzed steps ensure specific outcomes for the needs of the cell
Making the chemical building blocks (ex. amino acids) of the cell
Harnessing energy from food and sunlight
The enzymes involved in many of the multi-step pathways that are so common in metabolism are located close together in the mitochondria
The compartmentalization of enzymes also contributes to controlling enzyme function
ENZYME REGULATIONEnzyme function is controlled by molecules that
MaskBlock the active site Alter
When the molecule increases the productivity of the enzyme, it is an activator
When the molecule slows down or prevents an enzyme from doing its work, it is called enzyme inhibitionThe molecule that interrupts the enzyme is the inhibitor
There are two main kinds of inhibition: Competitive and Non-competitive
COMPETITIVE INHIBITION• Competitive inhibitors bind
reversibly to the active site and block the desired substrate from binding to the enzymeE + S ES E + PE + I EI
• The metabolic reaction is halted until the inhibitor is removed
• In extreme cases, the inhibitor binding is permanent
Eg. Cyanide is an inhibitor that binds IRREVERSIBLY to the enzyme
COMPETITIVE INHIBITION
http://www.youtube.com/watch?v=6-b9IoPzKrY
NON-COMPETITIVE INHIBITION
In non-competitive inhibition, the inhibitor binds to a regulatory site (away from the active site) on the enzyme, causing a change in shape which prevents the substrate from binding to the active site
alters the active site rather than blocks it
ALLOSTERIC REGULATIONActivator and inhibitor molecules that bind to
the allosteric site
site on an enzyme that can be bound by other molecules to manage the enzyme’s activity
– enzyme changes shape when filled
o Activators open up and stabilize the active site to receive substrates
o Inhibitors close it upThe change in shape causes the activity
(effectiveness) of the enzyme to be either increased or inhibited
A molecule that increases enzyme activity in this way is called an allosteric activator
When it inhibits enzyme activity it is called an allosteric inhibitor
A CLOSER LOOK AT CYANIDE Cyanide refers to a compound that contains a
cyano group C≡N Most are highly toxic (it is the cyanide anion CN-
that is responsible for the toxicity) The cyanide anion binds irreversibly to the
enzyme Cytochrome C Oxidase Shuttles electrons in the Electron Transport
Chain Pathway is disrupted
Cells are no longer able to aerobically produce ATP Any tissue that produces ATP aerobically will
be affected Central nervous system, heart
In the end, the cells aren’t receiving enough oxygen, and die from cyanide poisoning
This is irreversible competitive inhibition! Initial effects of poisoning - headache,
faintness, vertigo, excitement, breathing difficulty, increased heart rate, and hypertension
Later effects include coma, convulsions, paralysis,
respiratory depression, pulmonary edema, arrhythmias, bradycardia, and hypotension, death
Cyanide is rapidly absorbed from the stomach, lungs, mucosal surfaces, and
unbroken skin