enzymes Flashcards
what are enzymes? (2)
● biological catalysts
● formation of enzyme-substrate complexes lowers activation energy
explain the induced fit model of enzyme action (5)
● substrate and active site are not complementary
● active site changes and becomes complementary
● substrate binds to active site - enzyme substrate complex
● active site puts pressure onto bond and hydrolysis happens quicker
● this reduces activation energy
how have models of enzyme action changed over time? (2)
● initially lock & key model - rigid shape of active site complementary to only 1 substrate
● currently induced fit model - where enzymes are not a rigid structure and various parts of an enzyme molecule move in response to its environment
what are the 5 factors that affect rate of enzyme controlled reactions?
● enzyme concentration
● substrate concentration
● concentration of inhibitors
● pH
● temperature
how does substrate concentration affect rate of reaction? (3)
● initially, amount of substrate is limiting rate of reaction (enzymes with empty active sites)
● after point of saturation, enzyme active sites are limiting factor and increasing conc does not affect rate of reaction
● increase number of enzymes to increase rate of reaction
how does temperature affect rate of reaction? (5)
● as temp increases, more KE, more successful collisions
● more enzyme substrate complexes
● as KE increases, hydrogen and ionic bonds break between amino acids (disulphide bridges don’t break)
● tertiary structure changes
● active site no longer complementary
how does pH affect rate of reaction? (5)
● increased pH alters charge of amino acid - pH changes charge of R group
● breaks ionic bonds between R groups
● tertiary structure changes
● shape of active site no longer complimentary to substrate
● no enzyme substrate complexes formed
what do enzyme inhibitors do? (2)
● reduce rate of an enzyme catalysed reaction by interfering with enzyme in some way
● effect may be permanent or temporary
what are the types of inhibiters? (2)
● competitive - temporary
● non-competitive - permanent
how do competitive inhibitors work? (4)
● similar shape to substrate
● binds to active site
● prevents enzyme substrate complexes
● temporary
how do non-competitive inhibitors work? (6)
● binds to allosteric site (different part of enzyme)
● changes tertiary structure of enzyme
● alters active site shape
● no longer complimentary to substrate
● substrate cannot bind - permanent
● increasing substrate has no effect on rate of reaction
explain how the active site of an enzyme causes a high rate of reaction (3)
● lowers activation energy
● induced fit causes active site to change shape
● so enzyme substrate complex causes bonds to form / break
how can you tell from a graph if a substance is a non-competitive inhibitor?
increased substrate concentration does not change rate of reaction / overcome inhibition
outline how to find rate of reaction from a graph (2)
● calculate gradient of line (change in x / change in y)
● or gradient of tangent to a point
