2.5 (Enzymes) Flashcards
What is an enzyme?
A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold
What is a substrate?
Reactant in a biochemical reaction
What is the active site and what is attracted to it?
Region on the surface of an enzyme to which substrates bind which catalyses the reaction
What happens to enzymes?
Once a substrate has been locked into the active site, the reaction is catalysed. The products are then released and the enzyme is used again
Outline the lock and key hypothesis.
The substrate and the active site match each other in two ways:
Structurally- The 3D structured of the active site is specific to the substrate. Substrates that don’t fit, won’t react
Chemically- Substrates that are not chemically attracted to the active site won’t be able to react
Outline the induced fit model and why it better explains enzyme activity.
- If the lock and key model were true, one enzyme would only catalyse one reaction. In actuality, some enzymes can catalyse multiple reactions
- As the substrate approaches the enzyme, it induces a conformational change in the active site- it changes shape to fit the substrate
- This stresses the substrate, reducing the activation energy of the reaction
Discuss enzyme reactions.
- The coming together of a substrate molecule and an active site is known as a collision
- Most enzyme reactions occur when the substrates are dissolved in water
- All molecules dissolved in water are in random motion, with each molecule moving separately
- If not immobilized the enzyme can move too, however enzymes tend be larger than the substrate(s) and therefore move more slowly
- Collisions are the result of the random movements of both substrate and enzyme
The substrate may be at any angle to the active site when the collision occurs - Successful collisions are ones in which the substrate and active site happen to be correctly aligned to allow binding to take place
Discuss enzyme denaturation.
- The three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of amino acids within the molecule. Most of these bonds and interactions are relatively weak and they can be disrupted or broken. This results in a change to the conformation of the protein, which is called denaturation
- A denatured protein does not normally return to its former structure – the denaturation is permanent. Soluble proteins often become insoluble and form a precipitate
What are causes of enzyme denaturation?
- Heat can cause denaturation: vibrations within the molecule breaks intermolecular bonds or interactions
- Extremes of pH can cause denaturation: charges on R groups are changed, breaking ionic bonds within the protein or causing new ionic bonds to form
What does change in structure do to an enzyme?
For enzymes a change in structure means a change in the active site. If the active site changes shape the substrate is no longer able to bind to it
How does temperature affect the rate of activity of enzymes?
- Low temperatures result in insufficient thermal energy for the activation of a given enzyme-catalysed reaction to be achieved
- Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity
- This is because a higher kinetic energy will result in more frequent collisions between enzyme and substrate
- At an optimal temperature (may differ for different enzymes), the rate of enzyme activity will be at its peak
- Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the hydrogen bonds holding the enzyme together
- This causes the enzyme (particularly the active site) to lose its shape, resulting in a loss of enzyme activity (denaturation)
How does pH affect the rate of activity of enzymes?
- Changing the pH will alter the charge of the enzyme, which in turn will protein solubility and may change the shape of the molecule
- Changing the shape or charge of the active site will diminish its ability to bind to the substrate, halting enzyme function
- Enzymes have an optimum pH and moving outside of this range will always result in a diminished rate of reaction
- Different enzymes may have a different optimum pH ranges
How does substrate concentration affect the rate of activity of enzymes?
- At the optimum concentration of substrate molecules, all active sites are full and working at maximum efficiency
- Any increase in concentration beyond the optimum will have no added effect as there are no extra active ites to be used
What are common uses of enzymes in industry?
- Detergents contain proteases and lipases to help breakdown protein and fat stains
- Enzymes are used to breakdown the starch in grains into biofuels that can be combusted
- In the textiles industry enzymes help in the processing of fibres, e.g. polishing cloth to make it appear more shiny
- In the brewing industry enzymes help a number of processes including the clarification of the beer
- In Medicine & Biotechnology enzymes are widely used in everything from diagnostic tests tests to contact lens cleaners to cutting DNA in genetic engineering.
- Enzymes are widely used in the food industry, e.g.
fruit juice, pectin to increase the juice yield from fruit
Fructose is used as a sweetener, it is converted from glucose by isomerase
Rennin is used to help in cheese production - Paper production uses enzymes to helping in the pulping of wood
What are advantages of enzyme immobilisation?
- Concentration of substrate can be increased as the enzyme is not dissolved – this increases the rate of reaction
- Recycled enzymes can be used many times, immobilized enzymes are easy to separate from the reaction mixture, resulting in a cost saving.
o - Separation of the products is straight forward (this also means that the the reaction can stopped at the correct time).
- Stability of the enzyme to changes in temperature and pH is increased reducing the rate of degradation, again resulting in a cost saving.
