Enzymes Flashcards
Importance of enzymes
- Metabolism - sum of all chemical reactions occurring in an organism
- Enzymes control metabolic reactions, which can either be anabolic (formation of molecules from smaller units) or catabolic (breaking down of molecules)
Example of an anabolic reaction?
DNA replication, which is controlled by the enzyme DNA polymerase
Example of a catabolic process?
Digestion - the enzyme maltase breaks down maltose in two molecules of glucose
Intracellular, extracellular (enzymes)
- Intracellular - working inside cells
- Extracellular - working outside cells
Example of extracellular enzymes
- Most extracellular enzymes are catabolic
- In multicellular organisms, digestive enzymes are secreted from cells into the digestive system
- Unicellular organisms, such as yeast and bacteria, secrete digestive enzymes into their immediate environment
How do enzymes work?
- Substrates collide with the active site of the enzyme
- The shape of the active site is complementary to the substrate
- The substrate binds to the active site to form an enzyme-substrate complex (ESC)
- Bonds in the substrates are placed under strain and break; the enzyme provides an alternative reaction pathway that reduces the activation energy required for the reaction
- An enzyme-product complex is formed and the product/s is/are released
Substrate
A reactant in an enzyme-catalysed reaction
Active site
The region of an enzyme to which substrates bind
Enzyme
- Biological catalysts that facilitate chemical reactions
- Enzymes lower the activation energy of a reaction
Lock and Key hypothesis
This suggests that the shape of the active site is an ideal fit for the substrate molecule and therefore is specific to one substrate
Induced-fit hypothesis
This suggests that initially weak binding by the substrate will alter the enzyme’s tertiary structure. This strengthens the temporary bonds between the substrate and the enzyme, and weakens bonds within the substrate
Effect of temperature on enzyme activity
- A rise in temperature will increase enzyme activity up to an optimum temperature - enzyme and substrate molecules gain kinetic energy and move faster, thereby increasing the chance of successful collisions
- Above optimum temperature, further increases in temperature reduce and eventually stop enzyme activity - weak bonds (e.g. hydrogen bonds) in the active site vibrate more, strain, and break (i.e. the enzyme denatures)
Effect of pH on enzyme activity
- Enzyme activity decreases when pH moves away from the optimum (either increasing or decreasing) - changes to H⁺ ion concentrations alter the changes on amino acids in the active site, which can prevent substrate molecules from binding
- A further change in pH can stop all enzyme activity - hydrogen and ionic bonds in the active site are broken, which causes a permanent change in the enzyme’s tertiary structure (i.e. the enzyme is denatured)
Effect of substrate concentration on enzyme activity
Reaction rate increases as substrate concentration rises but eventually plateaus (when Vmax, the maximum rate of reaction, is reached). Enzyme concentration becomes a limiting factor when Vmax is reached - a higher collision rate between substrates and active sites results in enzyme- substrate complexes (ESCs) forming at a greater rate. Reaction rate plateaus when one of the factors becomes limiting
Effect of enzyme concentration on enzyme activity
An increase in enzyme concentration will raise the reaction rate to a higher Vmax (at which point substrate concentration becomes the limiting factor) - a higher collision rate between substrates and active sites results in enzyme- substrate complexes (ESCs) forming at a greater rate. Reaction rate plateaus when one of the factors becomes limiting