Enzymes Flashcards
What is an enzyme?
Enzymes increase the rate of reaction by lowering the activation energy of the reaction they catalyse. They are 3D tertiary structured globular proteins whose shape is determined by the primary sequence of amino acids
What is the active site?
An area of the enzyme that is made up of only a few amino acids and forms a small depression in the overall enzyme
What is the substrate?
The molecule that the enzyme acts upon
Describe the induced fit model
Enzymes are specific to substrates they bind to meaning that only one type of substrate fits into the active site of the enzyme. When the enzyme and substrate bind they form an enzyme-substrate complex, and the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate.
What are the factors affecting the rate of enzyme controlled reactions?
- Temperature
- pH
- Enzyme concentration
- Substrate concentration
- Concentration of competitive reversible inhibitors
- Concentration of non-competitive reversible inhibitors
Describe the factors affecting the rate of enzyme controlled in terms of Temperature
Rate of reaction increases up to the optimum temperature as the kinetic energy of the enzyme increases. Above the optimum temperature rate of reaction decreases beyond the optimum temperature as the enzyme becomes denatured.
Describe the factors affecting the rate of enzyme controlled in terms of pH
The pH of a solution is a measure of the hydrogen ion concentration. The pH of a solution can be calculated using the following formula: pH = -log10[H+].
A hydrogen ion concentration of 1x10-9, therefore, has a pH of 9. pH affects the enzyme’s shape as it can disrupt the bonds in the tertiary structure of the enzyme.
Like temperature, all enzymes work at different optimum pH’s e.g. pepsin in the stomach works in very acidic
conditions.
Describe the factors affecting the rate of enzyme controlled in terms of Enzyme concentration
The rate of reaction increases as enzyme concentration
increases, as there are more active sites for substrates to bind to, however increasing the enzyme concentration beyond a certain point, has no effect on the rate of reaction as there are more active sites than substrates so substrate concentration becomes the
limiting factor.
Describe the factors affecting the rate of enzyme controlled in terms of Substrate concentration
As the concentration of substrate increases, the rate of reaction increases as more enzyme-substrate complexes are formed. However, beyond a certain point, the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.
Describe the factors affecting the rate of enzyme controlled in terms of Concentration of competitive reversible inhibitors
As the concentration of competitive reversible inhibitors increases, the rate of reaction decreases as the active sites are temporarily blocked by inhibitors so substrates cannot bind to them.
Describe the factors affecting the rate of enzyme controlled in terms of Concentration of non-competitive reversible inhibitors
As concentration on non-competitive reversible inhibitors increases, the rate of reaction decreases as the shape of the enzyme (not the active site) is altered by the inhibitors.
What are intracellular enzymes?
The action occurs inside the cell, which produces the enzyme. For example, some enzymes in digestive systems are found in the cytoplasm of cells or attached to cell membranes and the reaction takes place inside the cell.
What are extracellular enzymes?
The action secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)
What is activation energy?
The minimum level of energy required to enable a reaction to take place. Enzymes work by lowering the activation energy of reactions
Name the two models of enzyme action:
The lock and key model
The induced fit model
