2.5 Enzymes Flashcards
Enzymes control the metabolism of the cell.
What is an enzyme?
A globular protein, acts as a biological catalyst by speeding up the rate of a chemical reaction. Enzymes are not changed or consumed by the catalysed reactions.
Typically names after the substrate & -’-ase’.’
What is an active site?
region on the surface of the enzyme which binds to the substrate molecule. Substrate and active site complement each other (shape and chemical properties), hence only a specific substrate is capable of binding to a particular enzyme’s active site.
Collision frequency
The rate of enzyme catalysis can be increased through improving frequency of collisions:
increasing molecular motion of particles (thermal - > kinetic) or increasing concentration of particles.
Reactions typically occur in aqueous solutions as the substrate and enzyme are moving randomly within the solution (Brownian motion). Enzymes may be fixed in position (e.g. membrane-bound), localising reactions to particular sites.
Enzyme catalysis
- Substrate binds to the enzyme’s active site > enzyme-substrate complex
- enzymes catalyses substrate into the product > enzyme-product complex
- enzyme and product dissociate, and the enzyme continue to catalyse reations
Effect of temperature on the rate of activity of enzymes.
low = insufficient thermal energy for the activation of an enzyme-catalyzed reaction
increasing temperature = increasing rate of reaction due to the increased motion of enzymes and substrate successful collisions
optimal temperature - rate of reaction is at its peak
high temperatures cause enzyme stability to decrease as thermal energy disrupts the enzyme’s H-bonds → causing the active site to lose shape, resulting in permanent denaturation.
*graph = increasing at an increasing rate + peaks + decreasing at a decreasing rate + 0
Effect of pH on the rate of activity of enzymes.
changing pH alters the charge of the enzyme, subsequently altering protein solubility and shape = diminishing ability to bind to the substrate - abrogating enzyme function
Moving outside of the optimal pH range rapidly diminishes enzyme activity.
*graph = similar to temp, more balance peak.
Effect of concentration on the rate of activity of enzymes.
Increased concentration = increased chance of successful collision within a given period. After a certain point, the rate of activity will cease to rise, regardless of the increase in substrate levels - the environment is saturated and all enzymes are bound and reacting (Vmax)
*graph = steep increase at an increasing rate + increasing at a decreasing rate + reaches a max concentration.
Enzymes can be denatured
The shape and chemical properties of the enzyme’s active site are highly dependent on tertiary structure.
Disruption to the chemical bonds that arenecessary to maintain the tertiary structure → changes to the structure of the active site (denaturation) = negative impact on enzyme’s capacity to bind to substrate.
Immbolised enzymes used in industry
Immobilised enzymes - fixed to a static surface in order to improve the efficiency of the catalysed reaction. Enzyme concentrations are conserved - not dissolved, retained for use. Thus, separation of product is more easily achieved
E.G. lactose-free milk production
How is lactose-free milk produced
lactose = disaccharide of glucose and galactose. The incidence of lactose intolerance is particularly high in Asian, African, and Aboriginal populations - lower in European populations due to mutation.
Method:
Can be produced by treating milk with the enzyme lactase (purified from yeast/bacteria). Lactase is bound to an inert substance (e.g. alginate beads). Milk is repeatedly passed through immobilised enzyme = lactose-free milk.
Advantages of lactose-free milk (4)
source of dairy for lactose-intolerant individuals
means of increasing sweetness without artificial sweeteners (sweeter)
reducing crystallisation of ice-creams (soluble, less likely to crystallise)
reducing production time for bacteria fermentation (e.g. cheese and yogurts)
