82 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
Immobilised enzyme (Key-Term)
Enzyme molecules bound to an inert material, over which the substrate molecules move.
How are enzymes immobilised?
Enzymes are immobilised when they are fixed, bound or trapped on an inert matrix such as sodium alginate beads or cellulose microfibrils.
How are immobilised enzymes packed?
These can be packed into glass columns.
What happens when substrate is added to the top of an immobilised enzyme column?
Substrate is added to the top of the column.
As it flows down, its molecules bind to the enzyme molecules’ active sites, both on the bead surface and inside the beads as the substrate molecules diffuse in.
What are the advantages of immobilised enzyme column?
Once set up, the column can be used repeatedly.
The enzyme is fixed and does not contaminate the products. The products are therefore easy to purify.
Where are immobolised enzymes used?
Why?
Immobilised enzymes are used widely in industrial processes, such as fermentation.
They are used because can readily be recovered for reuse.
What is the advantage of using smaller beads rather than larger beads when making immobilised enzymes?
If a given volume of material is used to make large beads, there will be a smaller total surface area than if the same volume had been used to make small beads.
So if small beads are made, the substrate molecules will have easier access to enzyme molecules and so they will produce a higher rate of reaction.
Why are enzymes that are free in solution not widely used?
Enzyme instability is one factor preventing the wider use of enzymes that are free in solution.
Organic solvents, high temperatures and extremes of pH can all denature enzymes, with a consequent loss of activity.
What is the advantage of immobilising enzymes with a polymer matrix?
Immobilising enzymes with a polymer matrix makes them more stable.
It creates a microenvironment allowing reactions to occur at higher temperatures or more extreme pHs than normal.
Trapping an enzyme molecule prevents the shape change that would denature its active site, so the enzyme can be used in a wider range of physical conditions than if it were free in solution.
What is the difference in the rate of reaction between enzymes immobilised in beads versus enzymes immobilised in membrane?
Enzymes immobilised in beads have a lower rate of reaction than those immobilised on a membrane, if all other factors are constant.
This is because some of the active sites are inside the beads and the substrate takes time to diffuse to them.
Enzymes on a membrane are readily available for binding, so they give a higher reaction rate.
Why are enzymes used in industry rather than inorganic catalysts?
Enzymes, rather than inorganic catalysts, are used widely in industry because they are more efficient.
They:
1. have a higher turn-over number
2. are very specific
3. are more economical as they work at lower temperatures.
Compare the effect of temperature on a free and immobilised enzyme.
High temperature can denature enzymes.
Immobilising enzymes with a polymer matrix makes them more stable.
It creates a microenvironment allowing reactions to occur at higher temperatures
Draw a diagram of an immobilised enzyme in a framework of cellulose microfibrils
Draw a graph showing the effect of temperature on the rate of reaction of an enzyme in the free and immobilised state
