3. Cofactors & Enzyme Inhibition Flashcards
What is essential for enzymes to work
Cofactors & Coenzymes
What are cofactors
- Some enzymes will only work if theres another non-protein substance bound to them. These are called cofactors.
- Some cofactors are INORGANIC molecules or ions. Work by helping the enzyme & substrate to bind tg. They dont directly participate in the reaction so arent used up or changed in any way.
Key example of a cofactor
Chloride ions (Cl-) are cofactors for the enzyme amylase
What are coenzymes
- HOWEVER, some cofactors are ORGANIC molecules - called coenzymes.
- They participate in the reaction & are changed by it (almost like a 2nd substrate). Often act as carriers, moving chemical groups between different enzymes. Theyre continually recycled during this process.
- Vitamins are often sources of coenzymes.
see pg47 for dia of cofactors & coenzymes
What can enzyme activity be prevented by
Enzyme inhibitors
What are enzyme inhibitors
- Molecules that bind to the enzyme that they inhibit.
- Inhibition can be competitive or non-competitive
COMPETITIVE INHIBITION
- Competitive inhibitor molecules have a similar shape to that of the substrate molecules.
- They COMPETE w 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 it.
_____ - How much the enzyme is inhibited depends on the relative concentrations of the inhibitor & the substrate.
- If theres a high concentration of the inhibitor, it’ll take up nearly all the active sites & hardly any of substrate will get to the enzyme.
- BUT if theres a higher concentration of substrate, the substances chances of getting to an active site before the inhibitor increase. So increasing the concent. of substrate will increase the rate of reaction to a point.
see dia and graph on pg47 of competitive inhibition
NON-COMPETITIVE INHIBITION
- Non-competitive inhibitor molecules bind to the enzyme away from its active site
- This causes the active site to change shape so the substrate molecules can no longer bind to it.
- They dont compete w the substrate molecules to bind to the active site bc they are a different shape.
- Increasing the concent. of substrate WONT make any difference to the reaction rate - enzyme activity will still be inhibited.
see dia and graph on pg48 for non-competitive inhibition
Inhibitors can either be
Reversible or Non-reversible
Which one they are depends on the strength of the bonds between the enzyme & the inhibitor.
NON-REVERSIBLE inhibitors
- If theyre strong, covalent bonds, the inhibitors cant be removed easily & the inhibition is irreversible.
REVERSIBLE inhibitors
- f theyre weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed & the inhibition is reversible.
What is End-product inhibition
- Enzymes can be inhibited by end-product inhibition.
____ - A metabolic pathway is a series of connected metabolic reactions. The product of the 1st reaction takes part in the 2nd reaction - & 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 on in the pathway
see dia on pg48 for end-product inhibition
simple
What are metabolic pathways regulated by
End-product inhibition
Metabolic pathways are regulated by End-product inhibition
- End-product inhibition is a way of regulating the pathway & controlling the amount of end-product that is produced.
EG:
- **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.
(see dia on pg49 for more sense)
- Both product & end-product inhibition are reversible. So when the level of product starts to drop, the level of inhibition will start to fall & the enzyme can start to function again - this means that more product can be made.
