Enzymes Flashcards
What are enzymes
Biological catalysts that speed up the rate of reaction, lowering activation energy, without being used up.
They are 3rd globular proteins in a tertiary structure.
They are specific so only catalyse one type of reaction and only complementary to one substrate
They have an active site that is complementary to shape of a specific substrate
What is activation energy and how do enzymes reduce it?
The extra energy required to enable a reaction to occur. Often supplied through heat in labs.
Enzymes are biological catalysts that lower activation energy to allow reactions to proceed quickly at lower temps in the body
What are the 2 models that show enzyme action?
The lock and key model
Induced fit model
What is the lock and key model?
Model that says the shape of the active site is complementary to the shape of the substrate.
The AS and substrate form an enzyme-substrate complex (ESC) that allows bonds to break or form more easily
What is the induced fit hypothesis?
Theory that says that as the substrate enters the active site and bonds to it, creating an ESC, the active site changes shape to form a tighter bond, putting a strain on the substrate, weakening it’s bonds to make them break easier, reducing activation energy.
What is an example of induced fit
Lysozyme:
Found in tears and egg white
Antibacterial as it hydrolyses the peptidoglycan in bacteri cell walls
Does this by catalysing the hydrolysis of glycosidic bonds, so chains of beta glucose are broken.
What are the types of reactions?
Catabolic reactions - involves breaking down or hydrolysis of larger molecules into smaller ones.
Anabolic reactions - larger molecules being made by condensation of smaller ones
Where are enzymes made and where do they operate?
All enzymes are made inside cells by protein synthesis but afterwards they function as intracellular or extracellular enzymes
What are intracellular enzymes?
Enzymes which remain inside cells e.g. DNA helicase
What are extracellular enzymes?
Enzymes that are secreted from cell to function e.g. amylase
What is an enzymes turnover number?
The maximum number of substrates it can convert into product molecules per unit time
Catalase can convert approximately 5 million molecules of hydrogen peroxide to water and oxygen per second
What is the effect on enzyme concentration on rate of reaction?
As enzyme concentration increases, rate of reaction increases.
This is because more active sites are available to form more enzyme substrate complexes by there being more successful collisions, increasing ROR
However the concentration of substrate can be a limiting factor.
What is the effect of substrate concentration on ROR?
As substrate conc increases, ROR increases.
This is because more substrate leads to more successful collisions and more ESC’s forming, so ROR increases
Vmax is reached when all available active sites are occupied and enzymes working at optimum.
The substrate are queuing up for active sites.
Enzyme conc is the limiting factor
Effect of temperature on ROR
At first, as temp increases, the kinetic energy of the substrate and enzyme molecules increase.
This means there are more successful collisions so increased number of ESC’s.
Therefore more product is produced in a shorter time, so ROR increases.
- then an optimum temp is reached
- then above the optimum, the molecules vibrate to point at which the hydrogen bonds in the tertiary structure of the enzyme break, changing shape of the enzyme so active site changes and no longer complementary to substrate. It has been denatured
What is the effect of pH on ROR
Different enzymes have different optimum pH’s, which is where the enzymes function most efficiently and ROR is highest. ROR decreases away from optimum.
This is because:
- pH is a measure of H+/OH-
Acidic = high number of H+
Alkaline = high number of OH-
- H+ and OH- charges interferes with the charges which bind the active site to the substrate, thus preventing ESC’s and ROR decreases. Excess charges may disrupt gezogen bonds holding tertiary structure together
- this changes structure of enzyme and shape of active site so no longer complementary to substrate.
- this is denaturing
