1- enzymes Flashcards
enzymes have either
tertiary or quaternary structure
enzymes have an
active site which is the area of the substrate where the substrate binds
lock and key theory
- enzymes are specific to substrates they bind to
- only one type of substrate fits into the active site of the enzyme
induced fit theory
- when the enzyme and substrate form a complex, the structure of the enzyme is distorted so that the active site of the enzyme moulds around the substrate
- this weakens the bonds in the substrate and lowers the activation energy
enzyme definition
enzymes are biological catalysts which increase the rate of a chemical reaction by providing an alternative route that requires a lower amount of activation energy
temperature affect on enzymes
- the rate increases with temperature, as higher temperature increase the kinetic energy of molecules, leading to more frequent collisions between enzymes and substrates
- however, if the temperature exceeds the enzymes optimal range, the enzyme can denature, altering its active site and reducing its activity
pH affect on enzymes
- each enzyme has an optimal pH at which it performs best
- deviations from the optimal pH can disrupt the enzymes shape (due to changes in the ionic and hydrogen bonds that maintain the enzymes structure), rendering it less effective
substrate concentration affect on enzymes
- as substrate concentration increases, the rate typically increases because there are more substrate molecules available for enzymes to bind
- however, once all enzyme molecules are occupied (saturated), further increase in substrate concentration won’t increase the rate
enzyme concentration affect on enzyme
- an increase in enzyme concentration generally leads to an increase in the rate because there are more enzyme molecules available to catalyse reactions
- this relationship is typically linear, provided there’s a surplus of substrate
- if substrate becomes limited, increasing enzyme concentration will not further increase the rate
how is the initial rate of reaction measured for enzymes
finding the gradient of a concentration- time graph at t=0
why is it important to measure the initial rate of reaction at t=0
- it is better than measuring the average rate of a reaction over a longer period of time because most reactions are rapid, and the substrate concentration quickly declines, causing the rate to slow
- valid comparisons can only be made at the start of the reaction when controlled variables are the same for all levels of the independent variable
inhibitors
substances which stop the enzyme from binding to its substrate, they may be reversible or irreversible
competitive inhibition
- competitive inhibitors compete with the substrate for the active site of the enzyme, therefore preventing the substrate from binding
- this can be reversed by increasing the substrate concentration
non-competitive inhibition
- non-competitive inhibitors bind to the enzyme at an alternative allosteric site, which alters the shape of the active site, thus preventing substrates from binding to it
- this cannot be reversed by increasing substrate concentration
end-product inhibition
the end product of a multistep reaction acts as an inhibitor to the enzyme which catalyses the initial stage of the reaction
intracellular enzymes
catalyse reactions inside a cell
catalase
breaks down toxic H2O2 into water and oxygen
extracellular enzymes
catalyse reactions outside a cell
digestive enzymes
break down large, insoluble molecules into smaller, soluble ones
