1.4.2 - Enzymes Flashcards
1) What is an Enzyme?
Enzymes are proteins with a specific tertiary structure.
1) What is the active site of an enzyme and what is it’s function?
It is the functional part of the enzyme that binds to the substrate by becoming complementary to the shape of the substrate. This allows the formation of an Enzyme-Substrate Complex (E-S complex).
1) How do enzymes affect the activation energy?
Enzymes lower the activation energy, due to bending bonds, allowing chemical reactions to take place at lower temperatures than they would otherwise occur (e.g. body temperature).
1) Describe the INDUCED FIT model
● Enzymes have an active site with a specific shape.
● Before the reaction the active site is not complementary to the substrate.
● Induced fit causes the active site to change shape and becomes complementary as substrate binds
● An enzyme- substrate complex is formed
● This stresses and bends the bonds in the substrate which allows the reaction to occur
1) How might a change in the primary structure result in a non-functional enzyme?
● A change in amino acid sequence results in different R groups
● Results in a change in hydrogen / ionic / disulfide bonds
● Which results in a change in the tertiary structure
● Which changes the shape of the active site;
● Substrate is not complementary to the active site so no enzyme-substrate complexes form.
Description and explanation of the effects of temperature
As the temperature increases, rate of reaction increases
* E and S have more KINETIC ENERGY
* so there are more collisions
* more E-S complexes formed per second
When temperature exceeds optimum, the rate of reaction decreases
Because enzymes molecules have more KINETIC ENERGY so H-Bonds break so tertiary structure changes shape of active site changes no E-S complexes can form
Description and explanation of the effects of pH
- Changing pH changes the CHARGES on the R groups of amino acids
- Leads to changes in hydrogen and ionic bonds which changes tertiary structure
- Active site changes shape (is denatured) and is no longer complementary or specific to substrate
- Substrate will not bind with active site
- Fewer/ no ESCs formed
Description and explanation of the effects of substrate concentration
- As substrate concentration increases, rate increases because more E-S complexes are being made per second
- Substrate concentration is the limiting factor
- Then as substrate concentration increases further, there is no further increase in rate of reaction because ALL ACTIVE SITES are OCCUPIED
- Enzyme concentration is the limiting factor
Description and explanation of the effects of enzyme concentration
- As enzyme concentration increases, rate increases because the amount of enzyme is the limiting factor
- Then as enzyme concentration increases further, there is no further increase in rate of reaction BECAUSE the rate is limited by something else, e.g. the amount of substrate available
- Also the rate might be limited because the temperature is not high enough for the reaction to happen any faster
Description and explanation of the effects of competitive inhibitor
The competitive inhibitor has a similar shape to the substrate and is complementary to the active site. The active sites will be occupied. Fewer enzyme-substrate complexes can be formed.
The inhibitor no longer affects the rate of reaction at HIGH concentration of substrate. There is more chance of the substrate binding to the active site (instead of the inhibitor) and therefore forming E-S complexes
Description and explanation of the effects of non-competitive inhibitor
Non-competitive inhibitor binds to the allosteric site of the enzyme (not the active site).
* This changes the tertiary structure of the enzyme
* so the shape of active site has changed
* so the substrate is no longer complementary
* so fewer E-S complexes form
Even increasing the concentration of substrate does not allow the rate of reaction to reach the same rate as with no inhibitor. This is because the non-competitive inhibitor reduces the number of functional enzymes present
Describe the properties of non-competitive inhibitor
binds at allosteric site / a site away from active site
Binding causes change in the shape of active site
At high substrate concentration there will be less functional enzymes (active sites) available
At high substrate concentrations there are less enzyme-substrate collisions (as there are less available active sites)
Describe the properties of competitive inhibitor
binds to active sites of enzyme
Binding does not cause change in shape of active site
At high substrate concentration there will be functional enzymes (active sites) available
At high substrate concentrations there are more enzyme-substrate collisions (more chance of substrate colliding with active site than competitive inhibitor)
- What do we mean by ‘immobilized enzymes’?
An immobilized enzyme is when the enzyme is attached to a solid support so that it cannot mix freely with the substrate and product.
- How can enzymes be immobilized?
Enzymes can be immobilized in beads.
They can also be immobilized on things like ‘test strips’ like the ones used to test for the presence of glucose
- What are the advantages of using immobilised enyzmes?
Beads can be reused
Continuous process
Avoid end-product inhibition
Don’t need to separate the enzyme from the product
