Substrate-active Site
The overall 3D structure and the enzyme's amino acid sequence of the active site is specific to the substrate
This ensures that the active site binds to the substrate molecule, holds on to it and lowers the activation energy for the reaction
The enzyme changes its shape slightly to adapt to the substrate (induced fit)
The overall 3D structure and the enzyme's amino acid sequence of the active site is specific to the substrate
--> This ensures that the active site binds to the substrate molecule, holds on to it and lowers the activation energy for the reaction
The enzyme is highly specific and the induced shape change of the enzyme and substrate upon binding results in a proper alignment of the catalytic groups on its surface allowing the reacting to occur
Induced-fit model supersedes the lock-and-key model
Enzyme activity is the catalysis of a reaction by an enzyme:
The substrate(s) binds the active site of the enzyme because of its structural and chemical specificity
While the substrates are bound to the active site, bonds in the substrate are stressed or weakened causing it to change into different chemical substances (products of the reaction)
The products are separate from the active site, leaving it vacant for substrates to bind again
While some enzymes are embedded and immobilised within a membrane most enzymes and their substrates are found in solutions (cytoplasm)
Molecular movement is needed for the substrate and an active site to join
--> substances can collide
The greater the kinetic energy of enzyme and substrate the greater the chance of collisions
When enzymes and substrates are in solutions both are doing the movement
When an enzyme is immobilised within a membrane, the substrate has to do all the movement
Immobilised enzymes are also used as a cell-free preparations industrially in the preparation of lactose free milk
Enzymes are attached to an insoluble material or membrane with the substrate moving over it
--> this allows the of enzymes and avoids having to add enzymes to the sample
The formation of an enzyme-substrate complex overall depends on three important aspects:
The molecular motion of both, enzyme and substrate, which causes random collisions between molecules
--> all metabolic reactions occur in an aqueous solution, which enables the molecule's continual motion
The correct alignment and angle between substrate and enzymes affect the success of the collision
The speed of movement which is affected by the molecules size - substrates are usually smaller than enzymes, so their movement is faster
Structure can be altered by changes in pH or temperature
If the shape of the active site has changed significantly it becomes denatured
--> won't function anymore, and the enzyme-substrate specificity is compromised
High temperature causes denaturation as the extra energy leads to increased vibration with the molecule, breaking intra-molecular bonds within the protein
Changes in pH leads to a higher or lower concentration hydrogen ions in the solution - as a consequence, hydrogen bonds within the enzyme are broken