5) enzyme action and inhibition

Enzymes facts

Enzymes are tertiary structure proteins which catalyse reactions by lowering the activation energy

Known as biological Catalysts

They are large molecules

Only a small part of the enzymes attaches to a substrate to catalyse a reaction ( sitenknown as active site)

Active site facts

Is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein

Due to this specific active site, enzymes can only attach to substrates that are complimentary in shape producing an ENZYME SUBSTRATE COMPLEX

Two models of enzyme action

All reactions require a certain amount of energy before they occur known as activation energy

When enzymes attach to substrate they can lower the activation energy needed for the recation to occur, and therefore speed up rate of reaction

2 models that explain this are lcok and key model and induced fit model

Lock and key model

The enzyme is like a lock and the substrate is like a key that fits in due to it complimentarity in shape

The enzyme active site is a fixed shape

Due to random collisions the substrate can collide and attach to the enzyme. This forms an ENZYME SUBSTRATE COMPLEX

Once enzyme substrate complex has formed, the charged groups within the active site distort the substrate and therefore lower the activation energy

The products are then released and the enzyme active site is empty and ready to be reused

Induced fit model

The enzyme is like a glove and the substrate is you hand

( The empty glove is not exactly complimentary in shape to your hand, but when your hand enters it envales the glove to mould around your jand and become completely complementary)

The enzyme active site is induced, or slightly changes shape, to mould around the substrate

When the enzyme substrate complex pccurs, due to the enzyme moulding around the substrate it puts strain on the bonds and therefore lowers the activation energy

The products are then removed and the enzyme active site returns to its original shape

What are enzymes?

Proteins

Factors affecting enzymes

Enzymes which are proteins are sensitive to certain conditions

Temperature

pH

Substrate concentration

Enzyme concentration

Inhibitors

Describe temperature as a factor affecting the rate of enzymes

If the temperature is too low, there is not enough kinetic enegrybfor successfull collisions between the enzyme and the substrate

If the temperature is too high, enzymes denature, the active site chabges shape because tertiary structure bonds break and enzyme substrate complexes cannot form

Optimum temperature - temperature at which the rate of reaction happensfastest (curve)

Explain pH as a factor affecting rate of enzymes

Too high or low pH will interfere with the changes in the Amino acids in the active site

This can break the bonds holding the tertiary structure in place and therefore the active site changes shape

The enzyme denatures and few enzyme substrate complexes can form

Different enzymes have a different optimal pH

Explain how substrate and enzyme concentration can affect the rate of enzymes

If there is insufficient enzymes, then the enzyme active sites will become saturated with substrate ( too much) and not be able to work any faster

Explain how competitive enzyme inhibitors affect the rate of enzymes

1) compeititve inhibitors are similar in shape to the substrate and can bind to the active site

2) This preventd the substrate from binding and the reaction ocurring

3) if you add more substrate this will flood/ outcompete the inhibitors, lnocking them out of the active site

Explain how non- competitive enzyme inhibitors affect the rate of enzymes

1) non- competitive inhibitors bind to the enzyme away from the active site, the allosteric site

2) this causes the active site to change shape, and therefore, the substrate is no longer complimentary in shape and can no longer bind to the active site, regardless of how much substrate is added

What does the graph look like for the rate of reaction against the substrate concentration with no inhibitors, competitive inhibitors and non competitive inhibitors?

And why does the graph plateaus?

Plateaus because not enough enzymes to continue