3.6 Enzymes

Definition of enzyme and active site

Enzyme - globular protein that increases rate of a biochemical reaction by lowering activation energy threshold.

Active site - site on surface of an enzyme which binds to the substrate molecule.

Enzyme-substrate specificity

Enzyme-substrate specificity means that the active site and substrate complement each other in shape and chemical properties. Binding to active site brings substrate into close physical proximity, creating an enzyme-substrate complex. Enzyme catalyzes conversion of substrate into product, creating enzyme product complex.

Lock and Key Model can also be used to explain specificity. Enzymes and substrates share specificity (enzymes interact with small number of specific substrates that complement active site).

Effects of temperature, pH and substrate concentration on enzyme activity

Temperature

Higher temperature increase the kinetic energy of enzyme and substrate, meaning higher enzyme activity. At optimal temperature, rate of enzyme activity will peak. Higher temperature can also cause enzyme (bonds within) to break, resulting in denaturation in which the enzyme cannot function.

(alevelnotes.com)

pH

Changing the pH away from the optimum pH that the enzyme operates at alters the shape of the active site, which diminishes ability of enzyme to bind to substrate, abrogating enzyme function.

Enzymes have optimum pH, moving outside range will diminish enzyme function.

(wizznotes.com)

Substrate concentration

Increasing the substrate concentration increases enzyme activity; however, more substrate means enzymes and substrates will collide and react more.

However, continually increasing the concentration will have no further effect as all the substrates will be occupied by enzymes.

(rsc.org)

 

Definition of denaturation

Denaturation - structural change in protein that results in loss (permanent) of its biological properties.

Use of lactase in the production of lactose-free milk

Lactose can be broken down into glucose and galactose, which is catalyzed by lactase. Mammals sometimes are lactose intolerant and produce less lactase after weaned.

Lactose free milk produced is purified by lactase (yeast/bacteria), binding it to inert substance (alginate beads).

Milk uses immobilized enzyme which is lactose free.