1.4.2 Enzymes Flashcards
What do enzymes do generally?
Act as catalysts without undergoing permanent change themselves
What are enzymes made of in terms of type of protein?
Globular proteins
What are enzymes structure?
Very specific precise tertiary structure
How many substrates fit an enzyme?
One enzyme for one type of substrate
Where does the substrate bind to the enzyme?
The active site
What is the active site? How is it formed?
A hollow depression on one side
Formed by the peptide, hydrogen, ionic and di-sulfide bonds in the tertiary structure
What describes the substrate shape compared to the active site?
Complementary
Why are enzymes needed in the body?
The activation energy of the majority of reactions are too high at the temperature in which living organisms exist
What is activation energy?
The least amount of energy required for a reaction to be able to take place
How do enzymes affect activation energy?
They reduce the activation energy
How do enzymes reduce activation energy?
Anabolic - The enzymes hold the substrate in such a way that they react more easily
Or
Catabolic - They put a strain on the bond that will more easily break
What are the two theories that describe the way enzymes work?
Lock and key
Induced fit
What is the lock and key hypothesis?
The enzyme and substrate appear perfectly complementary
They form and enzyme-substrate complex and then produces products
What does the lock and key theory suggest?
The structure of an enzyme is rigid when it isn’t
What is the induced fit hypothesis?
When the substrate enters the active site it induces a slight change in the shape of an enzyme due to temporary ionic bonding - this allows the enzyme-substrate complex to form
As the active site changes the enzyme puts a strain on the substrate molecule allowing products to be formed
What is denaturation?
When the active site changes due to changes in the tertiary structure of the molecule (usually hydrogen bonds - occasionally ionic if pH change) and so it is no longer complementary to the substrate
Enzyme-substrate complexes cannot form
What factors affect the rate of an enzyme controlled reaction?
Temperature
pH
Enzyme concentration
Substrate concentration
How do you express the rate of the enzyme controlled reaction?
The speed that the enzyme works in the turnover number
This is the number of substrate molecules which one enzyme molecule can turn into product per minute
How can rate be measured?
Increase in product over time
Or
Decrease in substrate over time
How do you work out the rate of reaction off a graph based on volume collected and time?
Draw a tangent to the curve of the graph and work out the gradient by doing Y / X
What do you have to do to acquire the results for the affect of temperature?
You have to do lots of experiments for different temperatures
What happens as temperature increases?
As more energy is added the enzyme and substrate molecules have more kinetic energy
Therefore there are more frequent successful collisions above the activation energy
More enzyme-substrate complexes form
More product produced
Faster rate of reaction
What is the optimum temperature for enzymes? Why?
37 degrees
Enzyme-substrate complexes form at the fastest turnover number before denatured as they have the most kinetic energy
What happens as temperature is increasing past 37 degrees or optimum temperature?
The enzyme becomes denatured
The high energy causes the hydrogen bonds to break
The tertiary structure will break down as the polypeptide chain unravels
The active site is changed
The substrate is no longer complementary
Fewer enzyme-substrate complexes form
The rate of reaction decreases
How can pH reduce the rate of reaction?
The change in concentration of hydrogen ions disrupts the ionic bonding holding the tertiary structure together
It affects the charges in R-groups therefore the ionic temporary bonds with the substrate no-longer occur
Shape of the active site changes (denatures)
Substrate is no longer complementary
Fewer Enzyme-substrate complexes form
The rate of reaction decreases
How does substrate concentration affect the rate of enzyme reactions?
Initial increase in rate of reaction
Gradual increase to plateau
Eventual plateau as there are only so many enzymes to form enzyme-substrate complexes therefore the rate of reaction can only go so far
As the volume of enzyme is reduced why does the rate of reaction decrease?
There are less enzymes therefore less active sites available to deal with the substrate
There will be less enzyme-substrate complexes and less products reduced
Why does the product produced always stay the same - when changing the enzyme concentration?
There’s always the same amount of substrate to break down
It just takes longer with fewer active sites available
What are the two types of inhibitors?
Competitive
Non-competitive
How do competitive inhibitors work?
They combine with the enzyme molecules at the active site as they have a similar and complementary shapes to the substrate
They compete with the substrates for the active site - they are not permanently bound
This forms enzyme-inhibitor complexes
They reduce rate of reaction
Example of competitive inhibitors at work?
Antibiotics and other drugs can destroy bacteria by combining with the enzymes that allow bacteria to function
How do non-competitive inhibitors work?
The inhibitor binds to the enzyme somewhere other than the active site
This affects the hydrogen and di-sulfide bonding which alters the tertiary structure
The active site is changed and the substrate is no longer complementary
No enzyme-substrate complexes can form
In a question if a substrate and a random molecule is shown what should you recognise?
That the two are complementary and so the molecule is likely to be an inhibitor of the other
What is the control of metabolic pathways?
End-point inhibition
The end product of a series of reactions can prevent its own production
