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BIOLOGICAL REACTIONS AND ENZYMES - Coggle Diagram
BIOLOGICAL REACTIONS AND ENZYMES
Enzyme and biological catalysts
Enzymes carry out catalysis, speeding up the chemical reactions in living organisms while being unchanged at the end of the reactions.
Being unchanged means they are able to be reused.
Enzymes are specific - each one only catalysis one reaction.
Enzyme
- A biological catalyst that speeds up the rate of a reactions by lowering its activation energy.
Catalysis
- Increasing the rate of chemical reaction by adding a catalyst.
For reaction to occur, a certain level of activation energy is required.
Enzymes enable the reaction to occur with a
lower activation energy
. Meaning that
chemical reactions can occur at high rates
even at relatively low temperatures
(enzymes found in cells of living organisms)
Enzymes can both function either inter-cellularly or extracellularly. (Extracellular enzymes include the human digestive systems)
Enzymes are globular proteins
Tertiary structures maintained by Hydrogen, Disulfide and ionic bonds.
They have a region known as the active site.
The substrate enters the active site and an enzyme-substrate complex forms.
Products form and are then released from the active site. The enzyme is unchanged and is available to catalyse another reaction
Two theories on how enzymes act
The lock and key theory
The enzyme's active site is complimentary shape to the substrate.
The substrate enters the active site and an enzyme-substrate complex is formed. The products then form and leave the active site.
The induced-fit theory
The active site slightly alters its shape to fit the substrate
When the product is formed the active site then returns to its original shape.
Example
- Lysozyme - thought to work through the induced-fit mechanism
The rate of an enzyme reaction can be found from a graph
Measuring the concentration of the substrate or product over a time allows the rate of reaction to be calculated.
On exam graphs the rate if reaction is shown by the gradient of the line.
A steeper gradients indicates a faster rate of reaction.
Any factors that increases the number of successful collisions between active sites and the substrates per unit time will increased the rate of reaction
Enzyme action is affected by temperature
Other influences to the rate on an enzyme controlled reaction:
Temperature
pH
Substrate
Enzyme concentration
Competitive and non-competitive inhibitors
In lower temperatures the enzyme and the substrate have low kinetic energy. This reduces the rate in which the molecules move in a solution.
Few successful collisions between active site and substrate. Fewer enzyme-substrate complexes are formed and therefore fewer products are formed per unit of time.
The rate of reaction is dependent on temperature.
Temperature increases the enzymes and the substrate gains more kinetic energy, increasing the rate of movement by a molecule in solution.
Increasing the chance of successful collisions between active site and substrate. Leading to the formation of more products per unit of time. Therefore rate of reaction increases.
Optimum temperature will soon occur, (temperature reaches highest peak)
After optimum temperature the reaction decreases rapidly, this is due to enzyme's active site becoming denatured.
The hydrogen bonds holding enzyme's tertiary structure will break, which causes the site to change its shape, if the active site changes shape the substrate no longer fits inside and bind with the active site. This means no more enzyme- substrate complexes are formed therefore no product formed
As well as having an optimum temperature enzymes also have an optimum pH
The rate of the enzyme-catalyzed reaction is the highest at the optimum pH. If the pH of the solution either increases or decreases from the optimum, the rate of reaction falls.
A small change from the optimum can cause the enzyme to be temporarily inactivated. This is only a temperate change if the optimum pH returns to normal the enzyme will begin to work as normal.
A large change will cause the enzymes tertiary structure to change, altering the shape of the active site and resulting in the enzyme being permanatly denatured.
Salivary amylase, a digestive enzyme, has a slightly alkaline optimum pH while pepsin, a digestive enzyme found in the stomach has an optimum pH of 2. This allows it to maintain its maximum rate of reaction in the acidic conditions found in the stomach.
Substrate concentration influences the rate of an enzyme-controlled reaction
As substrate concentration increases the rate of reaction also increases. This is because the presence of more substrate molecules increases the chance of successful collisions between active site and substrate.
The rate of reaction continues to increase as substrate concentration does until a maximum rate of reaction is reached, when further increases in substrate concentration no longer increase the rate of reaction.
A maximum rate of reaction is reached because there is a fixed concentration of enzymes. At this point all the active sites of the enzymes are constantly occupied, so the maximum number successful collisions occurring, this means there can be no more increase in product formed per unit of time. As it is the enzymes that are preventing the rate of reaction from increasing further, we can say that the enzyme concentration is the limiting factor.
The rate of reaction can be further increases if the concentration of enzymes is increases. This addition of enzymes will increase the number of available active site. The rate of reaction would continue to increase if substrate concentration were increases. However, eventually the concentration of enzymes would again become limited factors
Enzyme concentration also affects the rate on enzyme reaction
As enzyme concentration increases the rate of reaction also increases.
This means that there is always enough substrate available to fill all available active sites.
This ensures that substrate concentration is not limiting factor for the rate of reaction
If the substrate is not excess, then a maximum rate of reaction will be reached and the graph will level off.
Enzyme inhibitors can impede an enzyme activites
There are two types of inhibitors competitive and non competitive
Competitive inhibitors have a similar shape to the substrate molecule of an enzyme
By having a similar shape to the substrate molecule, a competitive inhibitor is able to enter the active site of the enzyme and prevent the substrate from binding.
As the substrate cannot bind, enzyme-substrate complexes cannot form, products are not formed and therefore the rate of reaction is not as high as it would be if the inhibitor was not present
An example of a competitive inhibitor is malonic acid.
Non-competitive inhibitors cause the active site of the enzyme to change shape
Non-competitive inhibitors bind to an area of an enzyme other than the active site, known as an allosteric site, causing the active site of the enzyme to change shape.
This means that the original substrate molecule can no longer bind to the active site.
Examples on non-competitors:
Cyanide
Mercury