Enzyme revision (2.4) Flashcards
What are enzymes and what is their function?
Enzymes are 3D globular proteins made up of amino acids. They act as biological catalysts, as they speed up the rate of a reaction/ allow reactions to take place in conditions where it would not otherwise be possible.
What do the bonds in an enzyme do?
The amino acids that make up an enzyme interact and can form hydrogen bonds and disulphide bridges. These bonds hold the enzyme together in a specific shape, giving it its 3D structure.
What is the active site of an enzyme?
The active site is the part of the enzyme that catalyses (speeds up) chemical reactions.
What are substrates?
Substrates are the molecules that enzymes act upon
What happens when substrates bind to an enzyme?
An enzyme-substrate complex is formed.
What are the two proposed models to explain enzyme activity?
The lock and key model, and the induced fit model.
What is the lock and key model?
The lock and key model of enzyme activity state that enzymes have a particular shape that corresponds to the shape of a specific substrate.
This allows the substrate to fit perfectly into the enzyme’s active site.
The shape of the enzyme does not change to fit a substrate.
What is the induced fit model?
The induced-fit model of enzyme activity state that enzymes are flexible structures that do not have the exact same shape as their corresponding substrate before binding.
Instead, the enzyme moulds to fit the substrate perfectly, forming the enzyme-substrate complex.
When the final product is released the enzyme returns to its original shape.
What are the factors that affect enzyme activity?
Temperature Inhibitors PH Enzyme concentration Co-factors Substrate concentration (TIPECS)
How does temperature affect enzyme activity?
Every enzyme has a unique range of temperatures in which it can function.
Within this range, there’s a specific temperature where the rate of reaction is the fastest (optimum temperature).
Increasing the temperature causes the enzymes and substrates to collide more frequently with more energy. This increases the rate of reaction up to a point.
If the temperature increases too much, the bonds holding the enzyme in its specific shape will begin to break.
The enzyme will start to unfold and lose its shape. At this point, the enzyme is denatured.
If the temperature is too far below the enzyme’s optimum temperature, the frequency of enzymes and substrate collisions decreases.
This causes the rate of reaction to slow down or stop completely. Normal enzyme activity can be restored if the temperature is increased.
How does the pH affect enzyme activity?
Every enzyme has an optimum pH range.
A slight change in pH from the optimum range can disrupt the shape of an enzyme.
However, the bonds that have been disrupted by the change in pH can recover if the pH returns to the optimum level.
If changes from the optimum pH values are very extreme, the bonds within an enzyme can break, causing the enzyme to denature.
What are inhibitors and what do they do?
Inhibitors are molecules (usually poisons) that either alter the shape of an enzyme’s active site or bind to the enzyme so the active site is blocked.
When an active site is blocked, the substrate can no longer bind to the enzyme.
This slows down the rate of reaction and could prevent the reaction from taking place.
How does the concentration of enzymes affect enzyme activity?
As the concentration of enzymes of the same type increases, the rate of reaction will also increase.
This is because when there are more enzymes present, substrates will have a greater chance of successfully binding to an enzyme’s active site.
However, as the number of enzymes continues to increase, the rate of enzyme activity will eventually reach a plateau.
There will be a point where all of the available substrates will already be bound to an enzyme, meaning any new enzymes won’t have a substrate available to bind with. Therefore they will have no impact on the rate of reaction.
How does the concentration of substrates affect enzyme activity?
As the concentration of substrates increases, the rate of reaction will also increase.
This is because there are more substrates available that can successfully combine with the enzyme’s active site.
However, as the substrate concentration continues to increase, the rate of reaction will eventually reach a plateau.
This is known as a saturation point because the active sites of the enzymes are already saturated with substrate.
What are co-factors and how do they affect enzyme activity?
Some enzymes can’t catalyse their reactions by themselves and need the help of co-factors.
Co-factors are molecules that bind to an enzyme’s active site in a way that alters its shape. This helps the corresponding substrate to tightly bind with the enzyme.
Co-factors may be ions or organic molecules (co-enzymes).
Without co-factors, the substrate and enzyme would not fit together and the reaction would not take place.
