Enzymes: Baker Flashcards
What is an enzyme?
It is a biological molecule that increases the rate of reaction by lowering the activation energy without being used up.
What is the induced fit model?
The active site, which is a similar shape, molds around the substrate to form the enzyme-substrate complex.
What is the enzyme-substrate complex?
Binding of the enzyme and the substrate
What is the lock and key theory?
A substrate is specific to one enzyme because of the specific shape of its active site (like a key fitting a lock)
What is a co-factor?
A substance that must be present to ensure that an enzyme catalysed reaction takes place
What is a prosthetic group?
A permanently bonded, via a covalent bond, non-protein co-factor to an enzyme
What is an example of a prosthetic group?
Haemoglobin contains a haem prosthetic group, which in turn contains iron to bind to oxygen via oxidation
What is a co-enzyme?
Small molecules that temporarily bind to the active site of an enzyme just before/when the enzyme binds, to help lower the activation energy. They are chemically changed during the reaction.
What are examples of inter-cellular enzymes?
- Amylase (a carbohydrase) - this breaks down starch and is found in the saliva glands, the small intest and the pancreas
- Protease - this breaks down protein and is found in the stomach, the pancreas and the small intest
- Lipase - this breaks down lipids into fatty acids and glycerol, and is found in the pancreas and the small intest
- Catalase - this is found in the liver and catalyses the breakdown of hydrogen peroxide into water
What is an example of an intra-cellular enzyme?
- DNA-polymerase this links together nucleotides to form long strands of DNA molecules
How can substrate or enzyme concentration affect the rate of reaction?
-It increases the rate of reaction as there is a higher enzyme/substrate concentration so more enzyme-substrate complexes can form
-As the concentration of one starts to increase further, the rate at which the rate of rection increases, starts to decrease
-This will eventually plateau and reach the Vmax, the maximum rate of reaction that can be reached (it will be different depending on the reaction occurring) as the other reactant concentration, enzyme or substrate depending on the question, becomes the limiting factor and no new E-S complexes can form
How does temperature affect enzyme activity?
-Enzymes and substrate molecules will have kinetic energy
-As the temperature increases so does the kinetic energy of both the substrate molecules and the enzymes
-This results in more successful collisions between substrate and enzyme, forming more enzyme-substrate complexes, so the rate of reaction increases
-After a certain temperature, the kinetic energy of the enzymes starts to break the weak hydrogen bonding in the enzymes tertiary structure, causing the enzymes shape to be changed, and by extension the shape of the active site
-This is called denaturing and means that the shape of the active site is not complementary to the substrate and so no more enzyme-substrate complexes can form and the rate of reaction drops to 0
How does pH affect enzyme activity?
-If the pH of the surrounding environment deviates (increases or decreases) from the optimum pH (different for every enzyme) it will cause the enzyme to denature
-This is because the H^+ ions/OH^- ions disrupt the ionic and hydrogen bonding in the enzymes tertiary structure, causing the bonds to break
-This changes the shape of the tertiary structure of the enzyme and therefore that of the active site
-The shape of the active site is no longer complementary to that of the active site and so no enzyme-substrate complexes form (this will taper off evenly to either end of a graph)
Note: Any enzymes that have a very high or low optimum pH will contain more disulphide bridges in their tertiary structure
What are enzyme inhibitors?
Substances or molecules that decrease the rate of reaction of an enzyme controlled reaction by preventing the substrate from binding to the active site.
What are competitive inhibitors?
Molecules that bind to an enzymes active site, so preventing the similarly shaped substrate from binding, and forming an inhibitor-enzyme complex. This is usually reversible and the normal Vmax of the enzyme can be reached if the concentration of the substrate is increased, but at a lower rate, due to the higher likelihood of the enzyme binding with the substrate.
What are non-competitive inhibitors?
A molecule that changes the shape of the enzymes tertiary structure and therefore the shape of the active site by binding to a separate part of the enzyme, not the active site. This lowers the Vmax of the enzyme as certain enzymes can no longer form any enzyme-substrate complexes, and as the inhibitors do not compete with substrate molecules for the active site.
What is a reversible inhibitor?
An inhibitor that can both bind and unbind from an enzyme, allowing the rate of reaction to increase or decrease without actually stopping.
What is an irreversible inhibitor?
An inhibitor that produces a permanent change in the enzyme by either not unbinding or changing its shape, causing the rate or reaction to halt as the enzyme is rendered useless.
