Topic : 2 Molecular Biology

Active site

Active site: The area or the pocket on the enzyme where the substrate binds.
Enzyme: Proteins that catalyze chemical reactions (increase the rate by lowering the activation energy)
Each enzyme catalyzes a specific reaction for a specific substrate
Enzymes are not used up during the chemical reactions
Enzymes are very specific, because both the enzyme and the substrate possess specific complementary shapes that fit into one another. (lock-and-key)
The binding of the substrate to the enzyme causes the chemical bonds of the substrate to weaken.
This eventually causes the reactions that take place that form the products.
After the products are released, the enzyme can bind to another substrate, because enzymes are not used up in these chemical reactions.
The substrate and active site match each other in two ways: structurally and chemically.
Structurally: The 3D structured of the active site is specific to the substrate. Substrates that don’t fix won’t react.
Chemically: Substrates that are not chemically attracted to the active site won’t be able to react

Enzyme catalysis involves molecular motion and the collision of substrates with the active site

The coming together of a substrate molecule and an active site is known as a collision.
Most enzyme reactions occur when the substrates are dissolved in water.
All molecules dissolved in water are in random motion, with each molecule moving separately.
If not immobilized the enzyme can move too, however enzymes tend be larger than the substrate(s) and therefore move more slowly.
Collisions are the result of the random movements of both substrate and enzyme.
The substrate may be at any angle to the active site when the collision occurs.
Successful collisions are ones in which the substrate and active site happen to be correctly aligned to allow binding to take place.
Successful reactions only occur if the substrate and the active site of the enzyme are correctly aligned and the collide with sufficient KE

Denaturation of proteins

The three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of amino acids within the molecule. Most of these bonds and interactions are relatively weak and they can be disrupted or broken. This results in a change to the conformation of the protein, which is called denaturation and is permanent.
Enzymes are proteins and denaturation is a key to how enzyme activity is affected by temperature and pH.
Heat can cause denaturation: vibrations within the molecule break intermolecular 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

Explain the effect of certain factors on enzyme activity
Temperature :

Increasing temperature increases the kinetic energy of enzyme and substrate, leading to more frequent collisions and a higher rate of activity.
At a certain temperature an optimum rate of reaction is achieved.
Above this temperature the enzyme starts to denature and the rate of activity decreases.

pH:

Enzymes have an optimal pH for activity
At a higher or lower pH enzyme activity will decrease
This is because changing pH can alter the charge, shape and solubility of the protein molecule

Substrate Concentration:

Increasing substrate concentration increases the frequency of enzyme-substrate collisions, resulting in a higher rate of enzyme activity
When all enzymes in solution are reacting (i.e. substrate saturation), energy activity increases.
Substrate concentration will have no further effect and rate of reaction will reach plateau.

Immobilized enzymes are widely used in industry

Detergents contain proteases and lipases to help breakdown protein and fat stains.
Enzymes are used to breakdown the starch in grains into biofuels that can be combusted.
In the textiles industry enzymes help in the processing of fibres, e.g. polishing cloth to make it appear shinier.
In the brewing industry enzymes help a number of processes including the clarification of the beer.
Paper production uses enzymes to helping in the pulping of wood.
Enzymes are widely used in the food industry, e.g. fruit juice, pectin to increase the juice yield from fruit; fructose is used as a sweetener, it is converted from glucose by isomerise; rennin is used to help in cheese production.

Reasons for using enzymes:

Convenience – only small amounts of proteins dissolve in the reactions leaving only solvent and the products. This means the enzymes and products can be easily separated
Economics – The immobilized enzymes can be easily removed and recycled from the solution, saving money. Eg. Particular useful in the removal of lactase in the production of Lactose Free Milk.
Stability – Immobilized enzymes generally have a greater thermal and chemical stability than the soluble form of the enzyme
Reaction rate is faster because substrates can be exposed to a higher concentration of enzymes

Explain the use of lactase in the production of lactose-free milk

Lactose is a disaccharide sugar present in milk composed of monosaccharides glucose and galactose.
Lactase is the enzyme that breaks down lactose into its two monosaccharides.
Humans are born with the ability to digest milk (lactase produced) but as we grow older, most humans lose the ability to produce lactase in significant amounts.
If the lactose is broken down in milk before it is consumed, people that are lactose intolerant can drink the milk.
Some types of yeasts produce lactase.
Biotechnology companies can culture these yeasts and remove the lactase.
Milk is treated with lactase before distribution, allowing lactose intolerant people to consume milk and milk products.
Milk is passed (repeatedly) over the beads
The lactose is broken down into glucose and galactose
The immobilized enzyme remains to be used again and does not affect the quality of the lactose free milk
Lactose-free products are useful for lactose-intolerant individuals and limit the need for artificial sweeteners

Topic : 2 Molecular Biology – 2.5 Enzymes