ENZYMES

Enzymes

molecules that are organic catalysts, they speed up chemical reactions by lowering the activation energy of chemical reactions

Enzymes and Substrates

enzymebind to a molecule called a substrate (reactant), which upon binding the substrate undergoes a chemical reaction and forms a product, which then leaves the enzyme which remains unchanged and free to catalyse further reactions

Features of enzymes

1. reusable

2. specific

3. reversible

4. speed up, not create

5. have an active site

6. are proteins

7. are a subset of catalysts

8. act on entire biochemical pathways

9. end in ‘-ase’

10. above the arrow

Enzyme-catalysed reaction

each enzyme has an active site, which is were the substrate binds to as they are complementary in shape. when a substrate binds to an enzyme’s active site, together they form an enzyme-substrate complex, with the active site undergoing a conformational change to accommodate the substrate

Activation energy

the input of energy required to start a chemical reaction (enzymes need to collide with each other with enough energy to overcome the activation energy of the reaction)

Enzymes and biochemical pathways

chemical reactions often occur in a sequence called biochemical pathways. one enzyme will function to catalyse a substrate into a product, which will then become the substrate of the next reaction, which will need a different enzyme

Temperature

chemical reactions speed up as temp increase, as this gives molecules (eg. enzymes) more kinetic energy and they collide with each other more often

Optimal temperatures

each enzyme has its own optimal temp at which its activity is greatest, meaning that the enzyme and substrate bind most frequently

What happens when its too hot?

since enzymes are mostly proteins, they can denature if under temps that are too hot, where the bonds that create its tertiary and quaternary structures are broken down. denaturation causes an irreversible conformational change in the active site of the enzyme, causing the substrate to no longer fit

What happens when its too cold?

at very low temps, enzymes experience little to no activity and can freeze, but is reversible as they just slow down (the enzyme and substrate molecules move slower and collide less frequently)

Tolerance ranges

outside of the enzymes tolerance range, it is likely to denature or slow down/freeze

pH

enzymes have optimal pHs at which they function best. enzymes will denature is exposed to an environment that is above or below the optimal pH

Substrate concentration

if the enzyme concentration remain constant while the substrate concentration increase, then the rate of reaction will increase. a saturation point will be reached where there are so many substrate molecules that continuously occupy all active sites, that increasing the substrate concentration further will no longer increase the reaction rate

Limiting factors

a factor that prevents an increase in reaction rate. when the limiting factor is a reactant, it is called a limiting reagent. if you increase the amount of a limiting reagent, the reaction rate will increase.

Enzyme concentration

an increase in enzyme concentration can increase the rate of reaction, due to the large number of active sites for the substrate to bind to . a point will be reached where enzymes are in excess and the graph plateaus making enzyme concentration no longer a limiting factor

Inhibition

enzymes can be prevented from functioning properly by molecules know as inhibitors

Competitive inhibitors

`bind to an enzymes active site, blocking it so that the substrate is no longer able to attach. they must have a shape complementary to the active site

Non-competitive inhibitors/ allostreric inhibitors

bind to an enzyme at a site other than the active site (the allosteric site), causing a conformational change in the active site which prevents the substrate form binding

Reversible inhibitors

bind to the enzyme with bonds that are weak enough to be broken, meaning their effects are not permanent and can be reversed by being overcome from increasing the amount of substrate present

Irreversible inhibitors

bind to the enzyme with bonds that are strong and cannot be broken (regardless of how much extra substrate is present)

Inhibition of biochemical pathways

enzyme inhibitors play an important role in regulating a range of biochemical pathways. this can occur if the final product of the pathway acts as an inhibitor at an earlier stage (know as a self-regulating pathway)

Coenzyme

some enzyme require assistance from a cofactor to catalyse their reactions. coenzymes are a type of cofactor that are organic, non-protein molecules. coenzymes bind to the active site and donate energy (protons or electrons) and then cannot be immediately reused, after the reaction it leaves the enzyme and is recycled by accepting more energy so that it can assist in more reactions (the cycling of coenzymes)