Enzymes- Topic 2 Flashcards
what are enzymes?
-biological catalysts that speed up the rate of reaction without being used in the reaction itself
-globular proteins that have a specific shape (tertiary)
why are enzymes specific?
-so that they are specific in the reactions that they catalyze meaning one enzyme will only react with molecules of one substrate
where is the site of reaction in enzymes?
-the active site it has a highly specific shape and other molecules of different substrates wont fit into the active site
how do enzymes work?
-a substrate is converted into a product, the substrate first binds to the active site to form an enzyme substrate complex then the substrate is converted into a product while attached to the enzyme and finally the product is released
what is the lock and key hypothesis?
-the active site is complementary to the shape of the substrate so only one active site on each molecule and one substrate that will fit together
-the substrate fits into the enzyme like a key in a lock this specificity leads to the lock and key hypothesis
what are the forces that hold the enzyme and substrates in place?
-the forces that hold the enzyme and its substrate are weak temporary bonds e.g. usually hydrogen bonds
what is the induced fit model and how does it relate to enzyme activity?
-it has been discovered that competitors for an active site which are molecules of a similar shape to the substrate could fit, this could mean that the substrate and active site are a little flexible
-when the enzyme and substrate form a complex, structural changes occur so that the active site fits precisely around the substrate
what is the transition state in relation to the induced fit model?
-when a substrate molecule binds the active site changes shape and fits itself around the molecule which distorts it into forming the transition state
according tot he induced fit model what happens the enzyme after its finished the reaction?
-once the reaction has occurred and products are formed they move away from the active site as they can no linger fit
-the flexible enzyme returns to its original shape ready to bind to the next molecule of substrate
what is activation energy?
-the energy required to start a reaction is called the activation energy
-before a substrate can change into a product the substrate must overcome an energy barrier called the activation energy (Ea)
the larger the activation energy…
-the slower the reaction will be because only a few substrate molecules will by chance have sufficient energy to overcome the activation energy barrier
what is the equation for the transition state?
-substrate A + enzyme-> enzyme substrate complex -> product + enzyme
what do enzymes do to activation energy? how do they do this?
-lower it so that most molecules can easily get over the activation energy barrier and quickly turn it into products
-enzymes lower the activation energy by stabilizing the transition state and they do this by changing the conditions within the active site if the enzyme
what is a cofactor ?
-a non- protein chemical compound that is bound to a protein and is required for the protein’s biological activity
what are coenzymes ?
-an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction
what is a holoenzyme ?
-the complete active enzyme with its cofactor
what is a apoenzyme?
-the enzyme without its cofactor
what are the 6 factors that affect the rate of enzyme reactions ?
-temperature
-pH
-substrate concentration
-enzyme concentration
-competitive inhibitors
-non competitive inhibitors
what is a denatured enzyme?
-an enzyme that has lost its 3D or tertiary structure so it is no longer able to function
why does temperature effect the rate of enzyme reactions?
-all enzymes have an optimum temp at which the work the fastest- mammalians is 40 degrees
-an increase in temp provides more kinetic energy to the substrate molecules and the number of collisions between enzyme and substrate will increase so the rare of reaction will increase
-above the optimum temp the enzymes are denatured, the bond holding the structure together are broken and the active site looses its shape and will no longer work
why does pH effect the rate of reactions in enzymes?
-they have an optimum pH at which they work the fastest for most enzymes its 7 or 8 some like protease that in the stomach can work at pH 1
-if the pH changes much from the optimum the chemical nature of the amino acids can change which can disrupt the bonds and so the tertiary structure may break down and they enzyme can become denatured
why does the substrate concentration effect the rate of enzyme reactions ?
-it effects the rate of reaction until a certain point
-at low substrate concentrations there are lots of free active sites and so the rate of reaction is slow
-when more substrates are added more enzyme substrate complexes can be formed as there are more active sites filled and the rate of reaction will increases
-eventually increasing the amount of substrates will have no effect on the rate of reaction as the active sites are saturated so no more enzyme substrate complexes can be formed
-on a graph it produces a straight horizontal line after the peak
why does enzyme concentration effect the rate of enzyme reactions?
-at low concentrations there is lots of competition for the active sites and the rate of reaction is low
-as the enzyme concentration increase there are more active sites available and so the rate of reaction increases
-eventually increasing the amount of enzymes will have no effect because the concentration of substrates will become the limiting factor
-on a graph the rate of reaction will increase linearly until a peak which then levels off
what are inhibitors ?
-they inhibit the activity of enzymes which reduces the rate of reaction sometimes this is necessary to ensure that a reaction does not proceed too fast but other times it isn’t wanted
-there are two types competitive and non competitive
-they can be found naturally but also used artificially in drugs and pesticides
