1.4.2 Enzymes Flashcards
how do enzymes act as
biological catalysts?
-each enzyme lowers activation
energy of reaction it catalyses
-to speed up rate of reaction
what do enzymes catalyse
-a wide range of intracellular and extracellular reactions that determine structures and functions from cellular to whole-organism level
describe the induced-fit model of enzyme action
- substrate binds to (not completely complementary) active site of enzyme
- causing active site to change shape (slightly) so it is complementary to its substrate
- so enzyme-substrate complex forms
- causing bonds in substrate to bend / distort, lowering activation energy
describe how models of enzyme action have changed over time
● initially lock and key model (now outdated)
○ active site a fixed shape, complementary to one substrate
● now induced-fit model
explain the specificity of enzymes
- specific tertiary structure determines shape of active site
○ dependent on sequence of amino acids (primary structure) - active site is complementary to a specific substrate
- only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
describe and explain the effect of enzyme concentration on
the rate of enzyme-controlled reactions
● as enzyme concentration increases, rate of reaction increases
○ enzyme concentration = limiting factor (excess substrate)
○ more enzymes so more available active sites
○ so more enzyme-substrate complexes form
● at a certain point, rate of reaction stops increasing / levels off
○ substrate concentration = limiting factor (all substrates in use)
describe and explain the effect of substrate concentration on
the rate of enzyme-controlled reactions
● as substrate concentration increases, rate of reaction increases
○ substrate concentration = limiting factor (too few substrate molecules to occupy all active sites)
○ more enzyme-substrate complexes form
● at a certain point, rate of reaction stops increasing / levels off
○ enzyme concentration = limiting factor
○ as all active sites saturated / occupied (at a given time)
describe and explain the effect of temperature on the rate of enzyme-controlled reactions
● as temperature increases to optimum, rate of reaction increases
○ more kinetic energy
○ so more enzyme-substrate complexes form
● as temperature exceeds optimum, rate of reaction decreases
○ enzymes denature - tertiary structure and active site change shape
○ as hydrogen / ionic bonds break
○ so active site no longer complementary
○ so fewer enzyme-substrate complexes form
describe and explain the effect of pH on the rate of enzyme-controlled reactions
● as pH increases / decreases above / below an optimum, rate of reaction decreases
○ enzymes denature - tertiary structure and active site changes shape
○ as hydrogen / ionic bonds break
○ so active site no longer complementary
○ so fewer enzyme-substrate complexes form
describe and explain the effect of concentration of competitive inhibitors on
the rate of enzyme-controlled reactions
● as concentration of competitive inhibitor increases, rate of reaction decreases
○ similar shape to substrate
○ competes for / binds to / blocks active site
○ so substrates can’t bind
○ so fewer enzyme-substrate complexes form
● increasing substrate concentration reduces effect of inhibitors (dependent on relative concentrations of substrate and inhibitor)
describe and explain the effect of concentration of non-competitive inhibitors on the rate of enzyme-controlled reactions
● as concentration of non-competitive inhibitor increases, rate of reaction decreases
○ binds to site other than the active site (allosteric site)
○ changes enzyme tertiary structure / active site shape
○ so active site no longer complementary to substrate
○ so substrates can’t bind
○ so fewer enzyme-substrate complexes form
● increasing substrate concentration has no effect on rate of reaction as change to active site is permanent
