Cofactors Anf Enzmye Inhibiton Flashcards
some enzymes will only work if there is another non protein substance bound to them, what are these non-protein substances called?
Cofactors
What are Cofactors
Some cofactors are inorganic molecules or ions. They work by helping the enzyme and substrate to bind together. They don’t directly participate in the reaction so aren’t used up or changed in any way. For example, chloride ions (CH) are cofactors for the enzyme amylase.
Some cofactors are organic molecules, what are these called?
Coenzymes
What do coenzymes do
They participate in the reaction and are changed by it
(they’re just like a second substrate, but they aren’t called that).
They often act as carriers, moving chemical groups between different enzymes. They’re continually recycled during this process.
Vitamins are often sources of coenzymes.
What is a prosthetic group
If a cofactor is tightly bound to the enzyme, it’s known as a prosthetic group.
Prosthetic group example
For example, zine ions (Zn2+) are a prosthetic group for carbonic anhydrase Can enzyme in red blood cells, which catalyses the production of carbonic acid from water and carbon dioxide). The zinc ions are a permanent part of the enzyme’s active site.
What is a competitive inhibitor
Competitive inhibitor molecules have a similar shape to that of the substrate molecules
2) They compete with the substrate molecules to bind to the active site, but no reaction takes place.
3) Instead they block the active site, so no substrate molecules can fit in it.
How much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate.
5) If there’s a high concentration of the inhibitor, it’ll take up nearly all the active sites and hardly any of the substrate will get to the enzyme.
6) But if there’s a higher concentration of substrate, then the substrate’s chances of getting to an active site before the inhibitor increase. So increasing the concentration of substrate will increase the rate of reaction (up to a point).
What is a non competitive inhibitor
Non-competitive inhibitor molecules bind to the enzyme away from its active site.
The site they bind to is known as the enzyme’s allosteric site.
2) This causes the active site to change shape so the substrate molecules can no longer bind to it.
3) They don’t ‘compete’ with the substrate molecules to bind to the active site because they are a different shape.
4) Increasing the concentration of substrate won’t make any difference to the reaction rate - enzyme activity will still be inhibited.
Wat does it mean if inhibitor is irreversible
If they’re strong, covalent bonds, the inhibitor can’t be removed easily and the inhibition is irreversible.
Wat does it mean if inhibitor is reversible
If they’re weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed and the inhibition is reversible.
What determines if an Inhibitors is Reversible or Non-Reversible
Which one they are depends on the strength of the bonds between the enzyme and the inhibitor.
Some medicinal drugs are enzyme inhibitors, for example:
1) Some antiviral drugs (drugs that stop viruses like HIV)
transcriptase inhibitors inhibit the enzyme reverse transcriptase, which catalyses the replication of viral DNA.
This prevents the virus from replicating.
2) Some antibiotics - e.g. penicillin inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall and prevents the bacterium from regulating its osmotic pressure. As a result the cell bursts and the bacterium is killed.
What are metabolic poisons
Metabolic poisons interfere with metabolic reactions (the reactions that occur in cells), causing damage, illness or death - they’re often enzyme inhibitors. For example:
Metabolic poison examples
1)Cyanide is an irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiration reactions. Cells that can’t respire die.
2) Malonate inhibits succinate dehydrogenase (which also catalyses respiration reactions).
3) Arsenic inhibits the action of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions.
Why are some enzymes synthesised as inactive precursors?
Enzymes are sometimes synthesised as inactive precursors in metabolic pathways to prevent them causing damage to cells. For example, some proteases (which break down proteins) are synthesised as inactive precursors to stop them damaging proteins in the cell in which they’re made.
2) Part of the precursor molecule inhibits its action as an enzyme.
Once this part is removed
(e.g. via a chemical reaction)
the enzyme becomes active.
