Chapter 6- ENZYMES Flashcards
What are enzymes
These are globular proteins and biological catalysts that speed up reactions without undergoing permanent change.
These are specific; an enzyme only binds with a single type of substrate since their active site has a specific and complimentary shape to only one type of substrate. Different enzymes bind to different type of substrate.
They are needed to catalyse reactions at a cellular and whole organism level.
How are enzymes effective?
The energy required to break the original bonds, so that a reaction can proceed, is called the activation energy.
Enzymes speed up reactions by reducing the amount of activation energy needed.
The stages of substrate to product
Substrate + enzyme -> enzyme-substrate complex -> enzyme-product complex -> products
Lock and Key hypothesis
The shapes of the substrate and the active site of the enzyme is complimentary and specific. The substrate fits the active site of the enzyme like a fitting key does in a lock.
The interactions of the R groups within the active site and the substrate stabilise the enzyme-substrate complex.
What are the two types of enzyme reactions?
Catabolic and anabolic reactions
Catabolic reaction breaks down the substrate into two products
Anabolic reaction joins two substrates into one product
How does a catabolic reaction occur
The formation of the enzyme-substrate complex causes conformational changes in the shape of the substrate. This weakens the bonds holding together.
Less activation energy is now needed to break the bonds and for the reaction to proceed.
Why do the products leave the active site of the enzyme?
The products no longer fit into the active site so they move away, allowing the enzyme to be reused.
How does an anabolic reaction work
ATP is required to change the shape of the substrate and synthesise a larger molecule or product.
This product leaves the enzyme’s active site since it no longer fits
Why does each enzyme’s active site have a specific shape?
An enzyme is a globular protein which is formed at the tertiary structure.
The DNA structure determines the sequence, number and type of amino acids, forming the primary structure. This then determines the folds of the beta pleated sheets and the alpha helix, in the secondary structure. This then influences how this structure folds more to form the globular shape; as well as the position of the disulphide bonds, hydrogen bonds and the hydrophobic/hydrophilic interactions
How does the graph of rate of reaction look like
X axis- time (secs)
Y axis- Amount of product
The rate of an enzyme-catalysed reaction is higher at the start because the concentration of substrate molecules higher at start
At this stage, this is a higher chance of substrate molecules entering the active site.
This soon decreases and then levels off because active sites are occupied
So increasing the substrate conc has no effect
So enzyme conc is the limiting factor
What is the Q10 temperature coefficient
This is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 degrees centigrade.
A temperature increase of 10 degree centigrade is equal to the Q10 coefficient for that enzyme and can be used to compare the rate of reaction for different enzymes.
This is the ratio between the rates of that process at two different temperatures.
Temperature coefficient= rate of reaction at (x+10) degrees centigrade / rate of reaction at x degrees centigrade
Where x is any given temp
What is the Brownian Motion
Molecules, in solution move randomly and continuously, colliding with each other.
How does increasing the temperature affect the particles
Heat increases the kinetic energy of molecules, they move faster and collide more often and with a greater force
How is glucose produced
In a solution of water molecules and maltose molecules, add maltase enzyme molecules
This will cause all of these three types of molecules to continually collide with each other.
the collision between the water molecule and a maltose molecule with the active site of a maltase enzyme molecule, a reaction will take place and the product glucose will be produced.
Exam question: how does optimum temperature affect enzyme activity
Increased kinetic energy
Increased number of collisions and successful collisions ( those reaching activation energy) in a given time
More successful collisions means more enzyme-substrate complexes are formed. Maximum rate of reaction is achieved
more product
What does an optimum temp give you
At optimum temperature, the maximum rate of reaction is occuring
Why does an enzyme denature at a high temperature (above optimum)
Heat vibrates molecules straining bonds
Weak H bonds and ionic interactions break first, breaking the tertiary protein structure
Eventually the active site loses its 3D conformational shape; the tertiary structure unravels.
The enzyme is denatured and its irreversible
The heat does not affect the primary structure; the covalent peptide bonds are not broken
Exam question: how does a higher temperature affect the enzyme activity
Molecules have more kinetic energy
Collisions occur more frequently with more energy
Molecules vibrates which strains the bonds
H bonds and ionic interactions are broken
(Covalent peptide bonds are not broken)
Tertiary structure pr globular shape altered
Active site looses its complimentary shape
Substrate molecule no longer fits active site
Enzyme is denatured
Rate decreases
Irreversible so reaction really slows down
Effect of temperature on enzyme sctivity
Slow rate of reaction or activity Less kinetic energy Molecules moving slowly Few collisions (collisions less likely) Less collisions with sufficient activation energy Few enzyme-substrate complex formed Enzyme still works; not denatured
What is pH
It is a measure of H+ ion concentration
The higher the H+ concentration the lower the pH (acidic)
What can the H+ ions do
Disrupt the H bonds keeping the secondary structure in place
Ionic bonds holding the tertiary structure together
How can H bonds disrupt the alpha helix
As the conc of H+ ions is increased, the positive charge of this ion is attracted to the electronegative atoms, NOF. This ends up replacing the hydrogen bond.
How are the ionic bonds disrupted by H+ ions
H+ ions are attracted to the negatively charged group and so ‘cluster’ around it. This interferes with binding of the substrate to the active site.
Effect of pH at optimum
The solution contains the ideal no. Of H+ ions
The ionic bonding of the enzyme is not disrupted
The shape of the active site is not changed
Substrate fits forming enzyme-substrate complexes
Product is formed
Rate of reaction is at its max
Effect of pH either side of the optimum
Change in pH either side of the optimum provides less/more H+ ions
Ionic bonding is disrupted changing the tertiary protein structure
Active site changes shape so the substrate no longer fits
No enzyme-substrate complexes formed
No product formed
Mild pH change effects are reversible
Extreme pH can cause irreversible denaturation
What is enzyme inhibitor
It is a molecule that binds to an enzyme and decreases its activity
Since blocking an enzyme’s activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors.
They are also used to pesticides.
What are competitive inhibitors
The competitive inhibitor fits into the active site and so a substrate molecule cannot enter
It has a similar shape to the substrate
So it has a complimentary shape to the active site
What affects the effect of inhibition
The relative concentration of substrate and inhibitor molecules
More inhibitor molecules means more inhibitors collide with active sites and so the effect of inhibition is greater
