Chapter 3: Enzymes Flashcards
Describe the structure of an enzyme.
An enzyme is a globular protein which has hydrophilic R groups on the outside of its spherical shape ensuring its solubility and hydrophobic groups facing inwards. Enzymes also possess a cleft/depression known as the active site of the enzyme.
What are enzymes?
Enzymes are globular proteins which act as biological catalysts.
What is a catalyst?
A catalyst is a molecule which speeds up a chemical reaction but remains unchanged at the end of the reaction.
What is the lock and key hypothesis?
The idea that enzymes have specific active sites that are complementary to the shape of the substrate is known as the lock and key hypothesis.
What is the induced fit hypothesis?
The induced fit theory states that the enzyme and sometimes the substrate, can make conformational changes in order to ensure a perfect fit. This make catalysis even more efficient. So, as the substrate enters the active site, the enzyme can conform to form the enzyme-substrate complex.
What happens to the substrate after the enzyme-substrate complex?
It can either help in the formation of a product from one or more substrates or break down a substrate to make one or more products.
How do enzymes lower activation energy?
They lower activation energy by holding the substrate(s) in such a way that their molecules can react more easily.
What is activation energy? ref. enzymes
Activation energy is the minimum amount of energy required in a chemical reaction to break the bonds in reactant molecules. The enzyme lowers the activation energy of the reaction which they catalyse. However, the overall energy at the end of the reaction is maintained.
When is the rate of an enzyme-controlled reaction the fastest and what is it called?
At the beginning and it is known as the inital rate of reaction.
How can you work out that the differences in reaction rate of various solutions are caused by differences in enzyme concentration?
This can be determined by working out the initial rates of reactions for each of the solutions by calculating the gradient of the curve a given period after the beginning of the reaction.
Describe the course of an enzyme-controlled reaction. ref. rate
Initially, there are a large number of substrates and every enzyme has a substrate in their active site. This is the initial rate of reaction where the rate is always fastest. The rate at which reaction occurs depends on how many enzyme molecules there are and the speed at which the enzyme can convert the substrate into product. However, as more and more substrates are turned into products, there are fewer and fewer substrates. This reduces the rate of a reaction as the enzymes have to wait for substrate molecules to meet their active sites, until the reaction eventually stops.
What are the factors the affect the rate of a reaction?
Enzyme concentration, substrate concentration, pH, temperature
Describe how enzyme concentration has an effect on the rate of a reaction.
As the enzyme concentration is increased, there are more active sites to which substrate molecules can bind to. This means that there are more enzyme-substrate complexes formed and hence more products for a given period of time as compared to a solution with a lower enzyme concentration. The limiting factor is the enzyme concentration. Once all substrates have formed enzyme-substrate complexes, a further increase in concentration will have no effect on the rate of reaction. At this point, the limiting factor is the substrate concentration.
What is the effect of the substrate concentration on the rate of a reaction?
As the substrate concentration increases, there will be more enzyme-substrate complexes forming and more products, effectively increasing the rate of the reaction. The limiting factor is the substrate concentration. This is because as the substrate concentration increases, there comes a point when all the enzyme active sites are working continuously. If more substrate is added, the enzyme cannot work faster i.e. the substrate molecules are waiting for an active site to become vacant. The increase in substrate at this point will have no effect on the rate of reaction. The limiting factor at this point is the enzyme concentration. The maximum rate at which enzymes are working and occupied is known as Vmax.
What is the effect that temperature has on the rate of a reaction? ref. bonds
As temperature increases, the kinetic energy and enzyme activity increases as the frequency of collisions of the substrate with the active site increases. This pattern is seen until the optimum temperature is reached. This is when the maximum rate of reaction is achieved. If the temperature continues to increase beyond the optimum temperature, the rate of reaction begins to decrease. This is due to the enzymes becoming denatured. The denaturation of enzymes occurs due to the kinetic energy breaking the hydrogen bonds in the secondary and tertiary structure of the enzymes. This changes the shape of the enzyme and active site and causes the substrate to no longer fit.
