Session 4.4a - Lecture 2 - Enzymes Flashcards
Slides 1 - 28
Enzyme activity: kinetics and inhibition
- Role of enzymes
- How enzymes work
- Why they’re important
- How we can study enzymes
Enzyme activity:
- kinetics
- measurement
- inhibition
- measuring inhibition
Role of enzymes (start to introduce what proteins do)
Answer these for ILO.
What are enzymes?
Biological catalysts that increase the rate of chemical reactions by lowering the activation energy.
What is a chemical reaction simplistically?
A chemical reaction is where we’re starting with a substrate and ending with a product. In many cases this can be REVERSIBLE, we can go in the opposite way.
Which normally has lower energy - the substrate or the product?
The product
What is the energy change for reactions commonly measured in?
Gibbs free energy (the change in free energy)
What causes the energy change in substrate to product creation?
Making and breaking bonds
When we look at energy diagrams there is a barrier we need to get across. What is this known as?
The activation energy
What is the activation energy?
The minimum amount of energy a substrate molecule must have to form our product.
“Minimum energy S must have to allow reaction”
What is the transition state?
The state of a chemical midway between the substrate and product.
“High energy intermediate that lies between S and P”
(e.g. think about breaking a stick in two - the original stick is the substrate; when it is flexed in half to break it is the transition state; the final two pieces are the product)
Draw a simple chemical reaction.
S P
Fig. 2
Label this graph.
x-axis: Progress of the reaction –>
y-axis: Free energy, G
beginning: S Ground state
end: P Ground state
middle: Transition state (+)
- -> delta G+ S–>P (how much energy it takes to go from S to P)
- -> delta G+ P–>S how much energy it takes to go from P to S)
Draw an energy diagram for an enzyme.
See Fig. 2
x-axis: Progress of the reaction –>
y-axis: Free energy, G
beginning: S Ground state
end: P Ground state
middle: Transition state (+)
- -> delta G+ S–>P (how much energy it takes to go from S to P)
- -> delta G+ P–>S how much energy it takes to go from P to S)
What happens to the rate of chemical reaction without a catalyst?
The rate of chemical reaction will not be very fast as not many molecules will have the activation energy.
How can you increase the rate of reaction?
- Temperature
2. Concentration
Why does increasing the temperature increase the rate of reaction?
It increases the number of molecules with activation energy
- We give the molecules more energy so more of them are more likely to have the activation energy so they can overcome this intermediate state.
Why does increasing the concentration increase the rate of reaction?
Increases chance of molecular collisions
- pack in more molecules, if there’s more of them there’s more chance of them interacting so more chance for reaction to occur
Why is it difficult to use temperature to increase the rate of reaction in humans?
If I took you and heated you up to 50 degrees, your reactions might occur faster, but then you’d also be dead …
Why is it difficult to use concentration to increase the rate of reaction in humans?
E.g. glycolysis
- usually a few mM glucose in the cell
- could whack it up to 1 M glucose
- be much faster BUT
- much more serious problems because cells would explode
Why do cells explode if you take in too much glucose?
Because the cells would take in so much water and hence explode
Why can’t we change temperature or concentration to increase the rate of reaction in a biological system?
The cells/you would die due to HOMEOSTASIS
What is the idea of homeostasis?
To keep things as constant as possible (yes, there are small changes in concentration, metabolism etc., but not by many orders of magnitude).
If we can’t increase the rate of reaction by temperature and concentration, how can we?
By binding catalysts, or enzymes.
How do enzymes increase the rate of reaction?
They lower the activation energy (catalysed reactions over uncatalysed reactions)
What does lowering the activation energy do in reactions?
It means more molecules are likely to have enough energy to react - this is the basis of what an enzyme it.