2.5: Enzymes Flashcards
enzyme definition
A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold without being used up themselves (i.e. a biological catalyst)
substrate definition
reactant in a biochemical reaction
active site
region where substrate binds to enzyme and catalyses the reaction
lock and key hypothesis
will only react if:
structurally: 3d structure matches perfectly
chemically: chemically attracted to each other
why lock and key hypothesis is not true
means only one type of reaction can be formed by each enzyme but in reality more than one can occur
induced fit model
enzymes can catalyse multiple reactions
- when substrate approaches enzyme, induced conformational chnage in active site
- stress on substrate from this reduces activation energy of reaction
- enzyme reverts to original shape when substrate is released
collision
coming togetehr of substrate molecule and active site
random motion
when molecules are dissolved in water, each molecule is speratelt moving
collisions ar ethe result of
random movemtns of both substrate and enzyme
successful collisions
occur only when substrate and active site are aligned correctly
immobolized enzymes definition
are those that are attached to a material so that it stays in place
how do immobollized enzymes stay in place
- Bound to solid or porous materials
- Mixed in with a matrix
- Embedded in a soluble membrane
- Aggregations of enzymes bonded together
- Attached to surfaces, e.g. glass
- Entrapped in gels, e.g. alginate gel beads
examples of immobolized enzymes
- carbon capturing: polluted air is passed over enzymes, which traps CO2 for storage, reduces emissions from factories
- detergents: proteases and lipases to help breakdown protein and fat stains
Advantages of enzyme immobilization:
- Concentration of substrate can be increased as the enzyme is not dissolved
- Recycled enzymes can be used many times, immobilized enzymes are easy to separate from the reaction mixture, resulting in a cost saving
- Separation of the products is straight forward (this also means that the reaction can stopped at the correct time).
- Stability of the enzyme to changes in temperature and pH is increased reducing the rate of degradation, again resulting in a cost saving.
lactose intolerance?
not having enouhg lactase enzymes, can cause allergies
production of lactose free milk
- Lactase obtained from commonly from yeast
- Lactase is bound to the surface of alginate beads
- Milk is passed (repeatedly) over the beads
- The lactose is broken down into glucose and galactose
- The immobilized enzyme remains to be used again many times
Other uses of lactose free milk?
- sweetness of milk (glucose and galactose are sweeter in flavour)
- reducing the crystallisation of ice-creams (glucose and galactose are more soluble than lactose)
- shortening the production time for yogurts or cheese (bacteria ferment glucose and galactose more readily than lactose)
Denaturation of proteins?
three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of amino acids within the molecule are relatively weak and they can be disrupted or broken
- results in a change to the conformation of the protein, called denaturation
- does not normally return to its former structure – the denaturation is permanent. Soluble proteins often become insoluble and form a precipitate
causes of denaturation?
- Heat can cause denaturation: vibrations within the molecule breaks intramolecular bonds or interactions.
- Extremes of pH can cause denaturation: charges on R groups are changed, breaking ionic bonds within the protein or causing new ionic bonds to form.
denaturation of enzymes causes?
- change in structure means a change in the active site. If the active site changes shape the substrate is no longer able to bind to it
effect on temperature on enzyme activity
- Low temperatures result in insufficient thermal energy (lower activity)
- Increasing the temperature will increase the speed and motion of both enzyme and substrate (higher activity)
- optimal temperature: the rate of enzyme activity will be at its peak
- Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the hydrogen bonds holding the enzyme together (could also denaturize)
effect of pH on the rate of enzyme activity
- pH alters the charges on the active site of an enzyme and the surface of the substrate
- This can reduce the ability of both molecules to bind to each other
- optimum pH (peak), moving outside of this range (diminished rate of reaction)
- normally reversible when environment returns to optimal pH (ionic charges on active site are restored and enzyme can resume normal function)
effect of substrate concentration on enzyme activity
- rate of an enzyme catalyzed reaction increases in direct proportion to the substrate concentration until the reaction reaches a maximum rate
- not enough enzymes (enzymes become limiting factor) causes more competition for active sites, maximum efficiency, enzymes are saturated beyond here
- graph logs
effect of ENZYME concentration on enzyme activity
- enzyme concentration is increased, the rate of the enzyme
- assuming there is always excess of substrate, it is directly proportional
- linear positive graph
- substrate becomes limiting factor if not excess, becomes beyond the max rate of reaction
