cofactors and enzyme inhibition

cofactors/ coenzymes

non-protein substances that are bound to enzymes to make them work

cofactors which are inorganic molecules

They work by helping the enzyme and substrate bind together. They don’t directly participate in the reaction so aren’t used up or changed in any way

cofactors which are organic molecules

• these are called coenzymes

• they participate in the reaction and are changed by it

• they often act as carriers, moving different chemical groups between different enzymes

• they’re continually recycled during this process

• vitamins are often sources of coenzymes

competitive inhibition

• competitive inhibitor molecules have similar shape to that of the substrate molecules

• they compete with the substrate molecules to bind to the active site, but no reaction takes place

• instead they block the active site so no substrate molecules can fit in

• how much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate

• if there’s a high concentration of the inhibitor, it’ll take up almost all of the active sites and hardly any substrate will get to the enzyme

• 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 a substrate will increase the rate of reaction

non-competitive inhibation

• non-competitive inhibitors molecules bind to the enzyme away from its active site at a site called the allosteric site

• this causes the active site to change shape so the substrate molecules can no longer bind to it

• they don’t compete with the substrate molecules to bind to the active site because they have a different shape

• increasing the concentration of substrate won’t make any difference

inhibitors can be reversable or non-reversable

• if they’re strong, covalent bonds, the inhibitor can’t be removed easily and the inhibition is irreversible

• if they’re weaker hydrogen bonds or week ionic bonds, the inhibitor can be removed and the inhibition is reversable

end product inhibition

• a metabolic pathway is a series of connected metabolic reactions. The product of the first reaction takes part in the second reaction and so on

• each reaction is catalysed by a different enzyme

• many enzymes are inhibited by the product of the reaction they catalyse. This is known as product inhibition

• end product inhibition is when the final product in a metabolic pathway inhibits an enzyme that acts earlier in the pathway

How are metabolic pathways regulated by end-product inhibition

• phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP

• ATP inhibits the action of phosphofructokinase - so a high level of ATP prevents more ATP from being made

• both the product and end-product inhibition are reversable. So when the level of product starts to drop, the level of inhibition will start to fall and the enzyme can start to function again meaning that more product can be made