This IBDP Biology Blog is a recap of the previously learnt topic of enzymes, including additonal information such as how enzymes are used in the industry, let's get started!
Enzyme-Substrate specificity
Enzymes make it easier for a reaction to take place.
A substrate is a molecule upon which an enzyme acts. It binds to a specific area of an enzyme called the active site.
The substrate fits into the active site of the enzyme as a key fits into a lock. This is called the lock and key model of enzyme action. Shown below.
The 3 dimensional structure of a protein (ENZYME IS A PROTEIN) determines the shape of the active site. The substrate fits into the active site and reaction proceeds.
If a molecule has the "wrong" shape it cannot fit into the active site and will not react.
Therefore an enzyme only works with a specific substrate and only catalyzes a specific reaction.
Enzyme specificity is due to the complementary shape of the active site and the substrate
a) large globular protein enzyme
b) active site
c) substrate
d) Activated complex - substrate is weakened to allow the reaction
e) unchanged enzyme - can be reused at low concentrations
f) product of the reaction
The effects of temperature, pH and substrate concentration on enzyme activity
- how fast does the substrate dissapear?
- how fast is the product formed?
- Biological reactions are slow without the help of enzymes, so measuring the speed of the reaction also measures enzyme activity.
Temperature:
- Enzymes have an optimum temperature where activity is at it's highest. Usually around 37 degrees
- when temperature increases the kinetic energy of the substrate and enzyme molecules also increases, there are more collisions of the substrate with the active site.
- Almost all enzymes denatures above 60 degrees.
pH:
- Every enzyme works best at a certain pH, usually depending on the location
ie. Pepsin (stomach) - pH 2
Salivary amylase - pH 7.2
Blue curve = pepsin (a)= pH3, Red curve =salivary amylase (b)= pH 7.2
Concentration of substrate:
- Using a given amoutn of enzyme the reaction will go faster if the substrate is more concentrated
- at some point the enzyme active site is fully saturated and adding more will not increase rate of reaction.
Use of lactase in the production of lactose-free milk
Lactose - dissacharide (glucose + galactose) milk sugar
When a lactose intolerant person consumes a reasonable amount of milk, they will suffer from excess gas production and diarrhoea.
Food industry found a way to produce milk that contains almost no lactose.
It is done by:
1. attaching the enzyme lactase to a large molecules and then bringing it in contact with milk.
2. The lactose present breaks down into glucose and galactose by the lactase
3. Milk will taste sweet but will not cause problems for lactose intolerant people.
- lactase is
immobilised in alginate beads
- beads are placed in container over which milk can be
passed
- circulation
is maintained until all lactose has been converted.
- this means lactase can be
recovered and reused
- effecient conversion of lactose to glucose + galactose
That's it !
Drafted by Venetia (Biology)