2.1.4.2 - Many proteins are enzymes Flashcards
Topic 1
How do enzymes act as
biological catalysts?
● Each enzyme lowers activation
energy of reaction it catalyses
● To speed up rate of reaction
(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
- Specific Substrate binds to (not completely complementary) active site of specific 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● Initially lock and key model (now outdated)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
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 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
