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