Chapter 4- Enzyme Inhibitors And Cofactors Flashcards
What are inorganic 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.
Example of inorganic cofactor
Chloride ions (Cl-) are inorganic cofactors for the enzyme amylase.
What is an organic cofactor (coenzymes)
Some cofactors are organic molecules, these are called coenzymes. They participate in the reaction and are changed by it. They often act as carriers, moving chemicak groups between enzymes. They’re continually recycled during this process.
Example of coenzyme
Vitamins are often sources of coenzymes. For example, the coenzyme NAD is derived from vitamin B3.
What are prosthetic groups
If a cofactor is tightly bound to the enzyme, it is known as a prosthetic group
Example of a prosthetic group
Zinc ions (Zn 2+) are a prosthetic group for carbonic anyhydrase (an 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 are the two types of enzyme inhibition
1) competitive inhibition
2) non-competitive inhibition
What are competitive inhibitors
Competitive inhibitor molecules have a similar shape to that of substrate molecules. They compete with substrate molecules to bind to the active site, but no reaction takes place.
How much the enzyme is inhibited depends on the reactive concentrations of the inhibitor and substrate. If there is a high concentration of inhibitors, it’ll take up most of the ensyme’s active sites so the substrate cannot bind to it. However, rate will return to normal if inhibitor is removed.
What are non competitive inhibitors
Non competitive inhibitor molecules bind to the enzyme away from its active site. The site they bind to is called th allosteric site. This causes the enzyme’s active site to change shape so the substrate molecules can no longer bind to it.
Increasing the concentration of substrate won’t make any difference as enzyme activity is still inhibited.
Reversible and non-reversible inhibition
Inhibitors being reversible or not is dependant on the strength of the bonds between the enzyme and the inhibitor.
1) if they’re strong, covalent bonds, the inhibitor can’t be removed easily and the inhibition is irreversible
2) is they’re weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed and the inhibition is reversible.
Examples of medicinal drugs are enzyme inhibitors
1) some antiviral drugs eg reverse transcriptase inhibitors are a class of antiviral developed to treat HIV. They work by inhibiting the enzyme reverse transcriptase, which catalyses the replication of viral DNA. This prevents the virus from replicating.
2) some antibiotics- eg penicillin inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall and prevents bacterium from regulating its osmotic pressure. As a result the cell burst and the bacterium is killed.
What are metabolic poisons
Metabolic positions interfere with metabolic reactions, causing damage, illness or death- they’re often enzyme inhibitors.
Examples of metabolic enzymes
1) cyanide is a non competive, irreversible inhibitor of cytochrome C oxidase, an enzyme that catalyses respiration reactions. Cells that cannot respire die.
2) Malonate is a completitive inhibitor if succinate dehydrogenase (which also catalyses respiration reaction)
3) Arsenic is a non competive inhibitor of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions.
What is end product inhibition
A metabolic pathway is a series of connected metabolic reactions. Each reaction catalysed by a different enzyme. Many enzymes are inhibited by the product of the reaction they carouse. End product inhibition is when the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway. This controls the amount of end product made.
Example of end product inhibition
Phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP. ATP inhibits the action of this enzyme, so a high level of ATP prevents more ATP being made.
