Enzyme Inhibitors / Cofactors / Prosthetic groups Flashcards
(23 cards)
What are enzyme inhibitors?
A substance that slows down or stops the activity of an enzyme by interacting with the enzyme.
Why are enzyme inhibitors useful?
Inhibitors are needed in controlling the activity of enzymes - ensures the correct steps in the reaction pathway take place and regulates the rate and quantity of product formation.
What are competitive inhibitors?
An inhibitor with the same shape as the substrate combines with the active site, blocking access for the substrate.
They form enzyme-inhibitor complexes which are catalytically inactive.
How does concentration affect enzyme inhibition?
The amount of inhibition depends on the relative conc. of both substrate and inhibitor molecules.
- more inhibitor molecules = greater effect of inhibition.
Most enzyme inhibition is reversible by increasing substrate conc. If competitive inhibitors bind irreversibly to the AS, they are known as inactivators.
What are non-competitive inhibitors?
An inhibitor which combines with an allosteric site on the enzyme - changes the tertiary structure (conformational change) so the AS can no longer accept substrate.
What is meant by an allosteric site?
An area of the enzyme away from the active site.
How do non-competitive inhibitors impact rate of reaction?
The reduce the maximum rate of reaction - adding more substrate does not return the rate to it’s uninhibited maximum. The more inhibitor molecules, the greater the reduction in rate.
Non-competitive inhibitors can be reversible or irreversible.
What are reversible inhibitors?
The inhibitor combines temporarily with the enzyme - enzyme becomes active once more when the inhibitor is no longer attached.
How do reversible inhibitors work?
They form weaker hydrogen bonds / weak ionic bonds with the enzyme.
Their effect can be reversed by a change in the environment of the enzyme.
What are non-reversible inhibitors?
Inhibitors that combine permanently with an enzyme, completely inactivating it.
How do non-reversible inhibitors work?
They form strong covalent bonds with enzymes - e.g. metal ions form covalent bonds with sulphur containing R groups.
The cell must produce more of the enzyme - genes must be active to synthesise them.
What is end-product inhibition?
When the product of a reaction acts as an inhibitor to the enzyme that produces it.
- example of negative feedback
End product inhibition is reversible and non competitive.
Why are multi-enzyme complexes useful?
They increase the efficiency of metabolic reactions without increasing substrate conc.
What is an example of end product inhibition?
Breakdown of glucose:
- two phosphate groups added to glucose molecule
- phosphofructokinase catalyses breakdown of molecule
- ATP produced inhibits PFK enzyme.
What is meant by inactive precursors?
Enzymes can be secreted as inactive precursors to prevent them from causing cell damage e.g. protease - prevents autolysis.
Part of the precursor molecule is removed by a chemical reaction, activating the enzyme.
Give some examples of poisons / drugs which act as enzyme inhibitors:
- Poisons - cyanide, malonate, arsenic
- Drugs - penicilin , aspirin, statins, antivirals
What are enzyme cofactors?
Inorganic molecules or ions that are required by an enzyme for it to function. They may be permanent or temporary.
How do cofactors work?
They help the enzyme and substrate bind together but don’t directly participate in the reaction.
e.g. CL- ions are required for amylase to digest starch.
What are coenzyme?
Small, organic, non-protein cofactors.
They participate in the reaction and are changed by it e.g. B vitamins.
How do coenzymes work?
They often act as carriers - moving chemical groups between enzymes and can donate or accept hydrogen ions.
What is a prosthetic group in the context of enzymes?
A cofactor is known as a prosthetic group if it’s bound tightly to the enzyme - it contributes to the 3D shape of the enzyme.
e.g. Zn2+ ions are a prosthetic group for carbonic anhydrase and Fe2+ ions are a prosthetic group for Hb.
How do cofactors contribute to precursor activation?
Precursor enzymes need to undergo a conformational change to the AS structure to be activated.
- precursor enzyme before cofactor added = apoenzyme
- after cofactor added = haloenzyme
What is meant by zymogens / proenzymes?
These are precursor enzymes which undergo a conformational change due to change in environment rather than the addition of a cofactor.
