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factors affecting enzyme activity (temperature (extreme temperatures (cold…
factors affecting enzyme activity
temperature
increasing temperature increases kinetic energy of particles
particles collide more frequently
more frequent successful collisions between substrate and enzyme
increase in rate of reaction
temperature coefficient - Q10 - measure of how much rate of reaction increases with a 10 degrees C rise in temperature
usually 2 for enzyme-controlled reactions - rate of reaction doubles with 10 degrees C temperature increase
denaturation from temperature
enzymes are proteins - structure affected by temperature
higher temperatures - bonds holding proteins together vibrate more
temperature increases - vibrations increase until bonds strain and break
breaking of bonds changes precise tertiary structure of protein
enzyme changes shape and is denatured
active site changes shape - no longer complementary to shape of substrate
substrate can no longer fit into active sites - enzyme will no longer function as catalyst
optimum temperature - temperature at which enzyme has highest rate of activity
enzymes denatured above optimum temperature - decrease in rate of reaction is rapid
slight change in shape of active site means it is no longer complementary to substrate
enzymes below optimum temperature - decrease in rate of reaction - enzymes are less active but have not denatured
extreme temperatures
cold environments
adapted enzymes have more flexible structures, particularly at active site - less stable than enzymes working at higher temperatures
will denature at small temperature changes
hot environments
enzymes are more stable than other enzymes - increased number of bonds, particularly hydrogen bonds and sulphur bridges in tertiary structures
shapes of enzymes and active sites more resistant to change as temperature rises
pH
proteins are affected by changes in pH
hydrogen bonds and ionic bonds between amino acid R-groups hold proteins in their precise 3D shape
bonds result from interactions between polar and charged R-groups present on amino acids forming primary structure
change in pH refers to change in hydrogen ion concentration
more hydrogen ions present in low pH (acidic) environments
fewer hydrogen ions present in high pH (alkaline) environments
active site will only be in right shape at certain hydrogen ion concentration
optimum pH
when pH changes from optimum - structure of enzyme and active site is altered
if pH returns to optimum - protein resumes normal shape and can catalyse reaction again - renaturation
when pH changes significantly - structure of enzyme is irreversibly altered and active site is no longer complementary to substrate
enzyme is denatured - substrate can no longer bind to active sites
rate of reaction is reduced
hydrogen ions interact with polar and charged R-groups
changing hydrogen ion concentration changes degree of interaction
interaction of R-groups with hydrogen ions affects interaction of R-groups with each other
increased hydrogen ions present (low pH) - fewer interactions between R-groups
bonds break and shape of enzyme changes
decreased hydrogen ions present (high pH) - more interactions between R-groups
bonds form and shape of enzyme changes
shape of enzyme changes as pH changes - enzyme will only function within narrow pH range
substrate concentration
increased concentration of substrate - number of substrate molecules, atoms or ions in a particular area or volume increases
increased number of substrate particles - higher collision rate with active sites of enzymes - more enzyme-substrate complexes formed - rate of reaction increases
enzyme concentration
increased number of enzymes - increases number of active sites available in a particular area or volume - faster rate of enzyme-substrate complexes formed
Vmax - all active sites are occupied by substrate particles - no more enzyme-substrate complexes can be formed until products released from active sites
can increase rate of reaction by adding more enzyme or increasing temperature
increased enzyme concentration - higher Vmax can be reached
concentration of substrate becomes limiting factor - increasing substrate concentration allows rate of reaction to increase