1. Enzymes Flashcards
All enzymes are what type of proteins?
Globular
What level of protein structure does the active site have?
Tertiary
What do enzymes do to the activation energy of a reaction?
Lower it - this means the reaction can happen at lower temperatures
All enzymes are ________ catalysts
Biological
The 3D shape of an enzyme’s active site is…
Complementary to the shape of the substrate
What happens in the enzyme-substrate complex?
Temporary bonds form between substrate and the amino acids that form the active site
Describe the induced fit model of enzyme action
- enzyme is flexible
* substrate binds onto it: active site slightly changes shape, moulds around substrate
What happens as the active site changes shape?
It puts strain on the substrate, distorting it and making the reaction more likely to happen
What happens to the shape of the active site once the substrate leaves?
Goes back to its original shape
Lactase balls milk practical: what are the advantages to this compared to adding the enzymes directly into a milk carton?
- Can be reused/easy to reuse - in industry this saves resources
- Slightly more temperature-stable so harder to denature
Lactase balls milk practical: why were small beads used?
Large surface area for the milk to come into contact with the beads - more lactose can be broken down
Lactase balls milk practical: what was the reason that the milk was tested for glucose?
To show that glucose is only present because it is a monomer of lactose (i.e. only present when lactose is broken down with lactase)
Two definitions of rate of reaction
- Measure speed at which substrate levels fall
2. Measure speed at which product levels rise
4 factors that affect rate of enzyme-controlled reactions
- temperature
- pH
- substrate concentration
- enzyme concentration
What determines optimum temperature?
The strength of the bonds that hold the tertiary structure together
What is the optimum temperature for enzymes in the human body (and explain)?
Over 37°C - around 40
This allows some leeway for situations like having a hot drink, fever etc
Is denaturation temporary or permanent?
Permanent!
Explain temperature (x) against rate of enzyme activity (y) graph
- temp increases → enzymes & substrates gain KE → more successful collisions → more enzyme-substrate complexes form
- optimum temp: fastest rate of reaction
- above optimum temp: enzyme denatured (tertiary structure disrupted so active site loses specific 3D shape). No longer complementary to substrate → e-s complexes can’t form
What is pH a measure of?
hydrogen ion concentration
Formula for pH
-logbase10[H+]
Explain pH (x) against rate of enzyme activity (y) graph
- optimum pH is when rate of reaction is fastest
- as pH moves away from optimum, enzyme is denatured. Shape of active site disrupted → no longer complementary to substrate → e-s complexes won’t form
How does changing the pH disrupt the active site?
Change in pH alters charge on the R group so disrupts tertiary structure (i.e. active site)
Explain substrate concentration (x) against rate of reaction (y)
- More enzymes than substrates: as substrate conc. increases, at any one time more active sites can be occupied. Substrate concentration is the limiting factor.
- When number of enzymes = number of substrate molecules, reaction is at its fastest
- More substrates has no effect on rate of reaction: at any one time all the active sites are occupied. Enzyme conc. is now the limiting factor
Define limiting factor
The factor that is present in the least favourable amount and which therefore controls rate
Explain enzyme concentration (x) against initial rate of reaction (y)
- Enzyme conc is limiting factor: more substrate than enzyme. As enzyme conc increases there are more successful collisions and more E-S complexes form.
- Same number of enzyme & substrate particles - all active sites are occupied. Rate of reaction is fastest here.
- More enzymes than substrate molecules - substrate conc is now the limiting factor. Adding more enzymes doesn’t increase rate of reaction because all the substrate molecules are in an active site already.
What is an inhibitor?
A substance that reduces the rate of an enzyme-controlled reaction by affecting the enzyme.
What is a competitive inhibitor?
Similar shape to substrate
Doesn’t react with enzyme
Binds to active site to form an enzyme-inhibitor complex, blocking substrate’s access to active site
Are competitive inhibitors usually permanently bound to the enzyme’s active site?
NO
What is a non-competitive inhibitor?
Different shape to substrate
Binds to enzyme at the allosteric site (NOT active site!!)
Change the overall shape of the enzyme –> disrupts active site –> substrate can no longer bind to it (active site no longer complementary to substrate)
Explain substrate conc (x) against initial rate of reaction (y) with non-competitive inhibitor
Non-competitive inhibitor binds to allosteric site, so reduces # of active sites that are complementary to the substrate. This reduces the chance of successful collisions between a substrate and active site, so fewer E-S complexes will form.
Plateaus at a lower level.
Explain substrate conc (x) against initial rate of reaction (y) with competitive inhibitor
Competitive inhibitor and substrate compete for the active site. Increasing substrate concentration increases the chance that the active site will be filled with a substrate rather than an inhibitor.
What is a metabolic pathway?
A series of linked chemical reactions each catalysed by its own enzyme
Describe how the final product of the metabolic pathway can act as an inhibitor of the first step
The final product acts as a non-competitive inhibitor by binding to the allosteric site of the first enzyme, so preventing any more product from being produced.
What is the advantage of this sort of end-point inhibition (i.e. when product acts as non-competitive inhibitor)?
Prevents waste
4 marker: explain the effect of a competitive inhibitor on the rate of an enzyme-controlled reaction
- binds to enzyme’s active site
- similar shape to substrate
- blocks substrate’s access & prevents the formation of enzyme-substrate complexes
- rate decreases
