7.6 Enzymes Flashcards
Describe a chain pathway
Moves from one reaction to the next (linear). Each product is the substrate in the next reaction. Each substrate has it’s own enzyme. The final product is called the end product.
Describe a cyclic pathway
Initial substrate is fed into a cycle where the final product is reacted with the initial substrate.
Describe the induced fit model
When enzymes and substrates bind, undergoes a conformational change to better fit the substrate. The induced fit model explains how an enzyme may be able to bind to, and catalyse, several different substrates (broad specificity).
Define activation energy
The minimum energy required for reaction to take place.
Describe how enzymes speed up reactions
Enzymes provide an alternative reaction pathway which requires a lower activation energy.
Describe competitive inhibition
Competitive inhibitors mimic the substrate, competing for the active site.
Describe non-competitive (allosteric) inhibition
Non-competitive inhibitors bind to the enzyme’s allosteric site, altering the shape so that the active site no longer functions.
Give an example of a competitive inhibitor
Penicillin blocks the active site of enzyme bacteria use to make their cell walls.
Give an example of a non-competitive inhibitor
Cyanide alters the shape of cytochrome oxydase in the electron transport chain, preventing ATP production through aerobic respiration.
Define the allosteric site
An alternative site on an enzyme where an additional substance can lock in.
Describe an allosteric enzyme
It has two sites: the active site where it binds with it’s substrate, and an allosteric site where it can bind with an additional substance.
Outline end-product inhibition
As the product molecules accumulate, the steps in their production are switched off. This is because the final product inhibits the enzyme that catalyses the first step in the pathway. However, these products become substrates in subsequent reactions. They are used up, and production of more molecules will recommence.
Give an example of end-product inhibition
ATP inhibits phosphofructokinase (an enzyme in glycolysis), so that when ATP levels are high, glucose is not broken down (but instead stored as glycogen). When ATP levels are low, phosphofructokinase is activated and glucose is broken down to make more ATP.
Outline how enzymes catalyse reactions
- Activation energy is energy needed to overcome energy barriers that prevent a reaction
- Enzymes increase the rate of chemical reactions by lowering activation energy
- They remain changed at the end of the reaction
- Substrate joins to enzyme at active site to form enzyme-substrate complex
- Enzymes are specific for a particular substrate
- Enzymes make the substrate more reactive
