Enzymes Flashcards
what is an enzyme
an enzyme is a biological catalyst
- increase the rate of reaction/make reactions faster therefore they are catalysts
speeds up reactions/speeds up breakdown
e.g. catalase - speeds up breakdown of hydrogen peroxide into water and oxygen
since they are found in living organisms
Describe the structure of enzymes
on the surface of an enzyme molecule there is a groove called the active site
on the surface, the tertiary structure of the enzyme folds into a three dimensional shape called the active site
Explain why enzymes are specific
The tertiary structure of the active site is complementary to the tertiary structure of a specific substrate molecule
the substrate molecule fits perfectly into the active site
because of this each enzyme is specific for the substrate it binds to
enzyme _______ and _______down another molecule
enzyme attaches to and breaks down another molecule
What is the substrate molecule
The molecule that the enzyme attaches to is called the substrate molecule
What are the prodcuts
The molecules that are produced (from the reaction)
what types of proteins are enzymes
Enzymes are globular proteins
Hydrophilic amino acids on their surface
have any hydrophobic amino acids are buried within the centre of the protein
- this makes globular proteins soluble in water
role of the active site
The job of the active site is to attach to the substrate molecule
active site - part of the enzyme where the substrate molecule attaches to form the enzyme-substrate complex
when the substrate molecule binds to the enzyme’s active site what is made
when substrate binds to enzyme active site - enzyme-substrate complex
what happens if a molecule with a structure which is different to the shape of active site
A molecule with a structure different to the substrate/shape of active site cannot successfully bind to the active site
what happens when the substrate binds to the active site
The amino acids on the surface of the active site can form temporary bonds with the substrate molecule
these temporary bonds help to lower the activation energy of the reaction
The enzyme then catalyses the reaction to form the enzyme-product complex
now products are released from the active site
how do enzymes increase the rate of reaction
in any reaction - molecules must have a certain amount of energy before they can react. - CALLED THE ACTIVATION ENERGY
any molecules which dont have at least the activation energy cannot react
enzymes provide a pathway for the reaction with a lower activation energy barrier
in the presence of an enzyme, the activation energy barrier is lower than it would be without the enzyme
this means that more substrate molecules now have enough energy (at least the activation energy) to cross the activation energy barrier and react
what happens to the reaction rate in the presence of an enzyme
In the presence of an enzyme , the reaction rate increases.
describe the lock and key model for enzyme function
tertiary structure of the active site is fixed and does not change shape (scientists thought)
substrate slots perfectly into the active site
shape of active site does not change when substrate binds
describe the induced fit model for enzyme function
the tertiary structure of the active site changes as the substrate molecule approaches
As the substrate starts to form bonds with the amino acids in the active site, the tertiary structure of the enzyme adjusts so that the active site moulds itself tightly around the substrate
this change in the tertiary structure of the enzyme, ensures that the active site fits perfectly to the substrate
the bonds that the substrate forms with the active site help to catalyse the reaction
tertiary structure of enzyme changes as substrate approaches so the active site moulds around the substrate
describe what would happen to molecules which are not the substrate
Molecules which are not the substrate cannot form the correct bonds to the correct amino acids in the active site
Because of this, the tertiary structure of the enzyme does not change - means that the shape of the active site does not adjust to fit the molecules
explains why enzymes are specific for their substrate
Compare the lock and key model and the induced fit model for enzyme function
shape of active site does not change when substrate binds - lock and key
tertiary structure of enzyme changes as substrate approaches so the active site moulds around the substrate - induced fit
describe what happens in an enzyme controlled reaction
in an enzymes controlled reaction, a substrate molecule is converted into a product molecule
for this to happen - the substrate molecule must collide successfully with the active site of the enzyme
https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcSMPWdqQHv0lmo5vEwUxwYcgNpEpBqWBv0cC5hc8fQykD1PgcIh
describe how the rate changes over the course of the enzyme controlled reaction
at the start, the line is steep
This means that a large amount of product is produced in a short time
so the rate of reaction is rapid initially
Rapid initial rate
however as the reaction continues, the line becomes less steep
although we are still making product, the amount of product being formed in a given time is less than at the start
this tells us that at this point, the rate of reaction has decreased
reaction slowing down
at the end, the line is horizontal
this means that no more product is being made so the reaction has stopped
draw graph of amount of product/time
draw graph amount of reactant/time
https://mmerevise.co.uk/app/uploads/2022/11/Rate-of-Reaction-Product-e1669108738140.png
https://mmerevise.co.uk/app/uploads/2023/01/mass-of-reactant.png
explain why the rate changes as the reaction proceeds
rate of an enzyme controlled reaction
rate of enzyme controlled reaction depends on the frequency of successful collisions between the substrate molecules and the active site
frequency = no. of collisions per second
at the start, there is a large amount of substrate molecules
this means that there is a high frequency of successful collisions between the substrate and the active site
this gives us a rapid initial rate of reaction
As the reaction takes place, some of the substrate is converted to product
this means that the amount of substrate molecules falls
So there is a lower frequency of successful collisions between the substrate and the active site (chance of them colliding is lower)
this is giving us a lower rate of reaction/reaction is slowing down
finally at a certain point - end of reaction
All of the substrate molecules have been converted to product
There are no more substrate molecules left to collide with the active site
frequency of successful collisions between the substrate molecules and active sire = 0
at this point, the reaction stops
describe how to calculate the rate of an enzyme controlled reaction
plotting the amount of product formed against time on a graph
then draw a tangent at the point of the reaction we are interested in
factors which affect rate of enzyme controlled reactions
Temperature
pH
concentration of substrate molecules
concentration of enzyme molecules
concentration of competitive inhibitors
concentration of non-competitive inhibitors
describe and explain the effect of temperature on enzymes
on the rate of an enzyme controlled reaction
the rate increases as we increase the temp
this is because, the kinetic energy of both enzyme and substrate are increasing
because they are moving more rapidly, the chance that the substrate will collide with the active site increases (there will be more frequent successful collisions - chance of this is higher)
This increase in the frequency of collisions between the substrate and the active site causes the rate of reaction to increase
At a certain temp., the ate of reaction is at its maximum
this is called the optimum temperature
At the optimum temperature, we have the maximum frequency of collisions between the substrate and the active site
as the temperature increases past the optimum, the rate of reaction decreases.
This is because at higher temperatures, the enzyme molecules are vibrating more rapidlyy
These vibrations cause bonds within the enzyme such as hydrogen bonds to break.
Because of this, the tertiary structure of the enzyme molecules begins to change
as the shape of the active site changes, there comes a point where it is no longer complementary to the substrate
now the substrate can no longer fit into the active site
At this point the enzyme has denatured and no longer functions.
so rate falls to 0
when an enzyme denatures due to high temperatures, it cannot renature if we cool it back down
this is because its tertiary structure has been changed so much that it cannot be reversed