enzymes Flashcards
what are enzymes?
biological catalysts
-increase rate of reaction by lowering the activation energy required for the reaction they catalyse
-3D tertiary structured globular proteins, shape is determined by the primary sequence of amino acids
what are enzymes specific to?
the substrates that they bind to
what happens when enzymes and substrates bind?
they form an enzyme substrate complex
induced fit model
an enzyme’s structure is altered so that the active site of the enzyme fits around the substrate that it has binded to
how does temperature affect the rate of enzyme controlled reactions?
-temperatures cause reactions to speed up
-molecules move more quickly as they have more kinetic energy
-increased kinetic energy results in a higher frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to more frequent enzyme-substrate complex formation
at very high temperatures, the enzyme denatures
what does denaturing cause?
-the increased kinetic energy and vibration of an enzyme puts a strain on its bonds, eventually causing the weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break
-the breaking of bonds causes the tertiary structure of the enzyme to change
-the active site is permanently damaged and its shape is no longer complementary to the substrate, preventing the substrate from binding
how does pH affect the rate of enzyme controlled reactions?
-pH affects the enzymes shape as it can disrupt the bonds in the tertiary structure of the enzyme
-all enzymes work at different optimum pH’s, at pH’s that aren’t these, the enzymes don’t work at their best
how does enzyme concentration affect the rate of enzyme controlled reactions?
-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
how does substrate concentration affect the rate of enzyme controlled reactions?
-as concentration of substrate increases, rate of reaction increases as more enzyme-substrate complexes are formed
-beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor
competitive inhibitors
-compete with the substrate for the active site
-the inhibitor molecule has a similar shape to the substrate molecule & competes with the substrate to bind to the active site of an
enzyme
-they block the active site so the substrate cannot bind, and no ES complexes are formed
non competitive inhibitors
-non competitive do not bind to the active site
-the inhibitor molecule can bind to a site on an enzyme that is not the active site (allosteric site)
-binding of the inhibitor to the alternative site results in a change in shape of the active site
-the enzyme is no longer able to bind to its substrate
how to reverse the effects of a competitive inhibitor
increasing the concentration of the substrate, the substrate will out-compete the inhibitor for the active sites
can you reverse the effects of a non competitive inhibitor?
no, increasing the concentration of the substrate will not affect the rate of reaction because they cannot bind to the active site
tertiary structure
the 3D shape of the polypeptide chain:
-creates a specific shape due to the sequence of amino acids in the chain
-hydrogen bonds, ionic bonds and disulphide bridges (covalent bonds) form between R groups
-a change to the sequence of amino acids would affect the tertiary structure as these bonds would form in different places
-all enzymes, antibodies and some hormones have tertiary structure
