Enzymes Flashcards
What type of protein is an enzyme?
Globular
Define enzyme
A biological catalyst that speeds up a reaction without getting used up, they do not experience any permanent damage.
Define activation energy
The minimum amount of energy that a chemical reaction requires to start
How do enzymes catalyse reactions?
They lower the activation energy by providing an alternative pathway for the enzymes with a lower activation energy barrier because of when the temporary bonds are formed between the substrate molecule and the amino acids on the surface of the active site
What is the shape of an enzyme the result of?
Their sequence of amino acids in their primary structure proteins, and the tertiary structure folds to form the enzymes active site
Describe the lock and key hypothesis
When a substrate molecule will only fit into a fit into the active site of one complementary enzyme.
Supported by the observation that enzymes are specific in the reactions they catalyse, the substrate will fit perfectly into the active site.
Describe a limitation of the lock and key model and how did this change enzyme models over time
Scientists observed that other molecules could bind to enzymes at sites other than the active site, altering the activity of the enzyme.
This shows that the structure of the enzyme is flexible not rigid, leading on to the induced fit model.
Describe the induced fit model for enzymes
Proposes that the active site changes as the active site and the substrate interact, the enzyme will change that forms the functional active site.
This shows the enzyme is flexible and can mould itself around the substrate. As the active site changes shape the enzyme puts a strain on the substrate distorting bonds in the substrate molecule, lowering the activation energy needed to break the bond
How would you describe the typical shape of a graph that measures rate of an enzyme controlled reaction?
At first there is alot of substrate with no products and it is very easy for the active site to come into contact with the substrate molecules. All enzyme active sites are filled constantly and the substrate is rapidly broken down to produce new products. The amount of substrate will decrease as it is broken down resulting in an increase in the amount of product, this makes it harder for substrate molecules to come into contact with enzymes because there is less substrate and products may get in the way. Takes longer for substrate molecules to be broken down so graph tails off , rate of reaction slows and graph eventually flattens
Describe the effect of temperature on enzyme actions
As temp inc kinetic energy inc meaning molecules move faster and there are more collisions between the enzyme and the substrate molecule. This means enzymes can inc the rate of reaction faster.
How is the effect of temperature on enzyme action shown on a graph?
There is a rising curve, however an extreme temp rise causes hydrogen bonds and other bonds in the enzyme molecule to break, resulting in the enzyme and the active site to change shape, at first the substrate will fit less easily into the active site slowing down the rate of reaction, at around 45 degrees, however when the enzyme is so distrupted that it stops working fully it is said to be denatured which is permanent, usually at 60 degrees
How does PH effect enzyme activity?
Change in PH changes the charges on the amino acids that make up the active site of the enzyme, as a result the substrate can no longer become attached to the enzymes active site so the complex cannot form, it may cause the bonds that maintain the enzymes tertiary structure to break so active site changes shape, enzymes may denature
What is the effect of enzyme concentration on the rate of reaction?
Increase in an enzyme conc leads to an inc in rate of reaction, because substrate molecules that were previously in excess are now being acted upon
What is a competitive inhibitor
They have a molecular shape to a substrate allowing them to occupy the active site of an enzyme
They compete with the substrate for the free active sites
The difference between the conc of substrate and the conc of the inhibitor that this determines the effect this has on enzyme activity.
If the substrate conc increases the effect of an inhibitor is reduced,
What is a non competitive inhibitor?
These attach themselves at binding sites that are not the active site of the enzyme.
When this attaches to a binding site of an enzyme, the enzymes shape will be altered so the tertiary structure will be changed so substrate molecules can no longer occupy it, less enzyme substrate complex forms
This means an inc in substrate conc does not decrease the effect of the inhibitor.
Compare the induced fit model and the lock and key theory of enzyme action
- Lock and key model is where the shape of the active site does not change when the substrate binds
- Induced fit theory is when the tertiary structure of enzyme changes as the substrate approaches so active site moulds around the substrate in order to have a specific, complementary fit
Why are enzymes described as specific in the induced fit model?
-Molecules which are not the substrate to the enzyme cannot form the correct bonds with the correct amino acids on the active site
- This means the tertirary structure of the enzyme does not change shape in order to fit with the incorrect substrate molecuke
How do competitive inhibitors reduce the rate of enzyme substrate reactions?
-The competitve inhibitor will occupy the active site for a short period of time
- This means the molecule prevents the actual substrate coliding with the active site and binding to form enzyme substrate complexes
- Because the frequency of collisions between the active site and the substrate is reduced, the effect of this molecule is to reduce the rate of reaction
- When a substrate conc inc, the effect of the inhibitor as a whole will decrease
How might a scientist stop an enzyme controlled reaction
- Boil the reaction to denature the enzyme
- Put in the freezer to lower kinetic energy so no enzyme substrate complex form
-Add a conc of enzyme inhibitor to reduce the frequency of enzyme substrate complexes forming
How does a competitive inhibitor decrease the rate of an enzyme controlled reaction?
- Inhibitor same shape as substrate
-Inhibitor binds to the enzymes active site - Prevents enzyme substrate complex forming
Describe how the structure of a protein depends upon the amino acids it contains
- Structure is determined by the relative position of amino acid interactions, this forms the primary structure
- Then the P structure forms the S structure due to hydrogen bonding between amino acids
- Then this forms the tertiary structure formed by r group interactions,
- Then this creates the specific shape of the active site on the enzyme
Explain how active site creates a high rate of reaction
It will lower the activation energy of the reaction
This is because the active site will change shape during induced fit to become complementary to the substrate molecule forming enzyme substrate complexes
This complex causes strain on bonds in the substarte breaking them lowering activation energy
