1: BIOLOGICAL MOLECULES - ENZYMES Flashcards
What do enzymes do?
act as biological catalysts (speed up metabolic reactions) both on a cellular level and for the organism as a whole
How do enzymes speed up reactions?
by lowering activation energy needed for the reaction to happen
What are the 2 ways in which enzymes lower activation energy?
- in anabolic reactions (synthesising larger molecules) : hold substrates close together so there’s less repulsion between the molecules so they can bond more easily therefore less energy is needed
- in catabolic reactions (breaking down substrate) : fitting into active site puts a strain on bonds that hold substrate molecule together so substrate breaks down more easily therefore less energy is needed
Describe the lock and key model
enzymes have a specific shape of active site that is complementary to a specific substrate
Why did scientists modify the lock and key model?
new evidence showed that in the enzyme-substrate complex the shape of the active site changed slightly to be even more specific to the substrate molecule
Describe the induced fit model
the active site is partially complementary to the substrate but as the substrate binds to the enzyme the active site changes shape slightly in order to become fully complementary to the substrate molecule (enzyme is altered)
Explain why enzymes are highly specific and what this means (5 marks)
- specific sequence of amino acids
- specific 3D tertiary structure
- active site has a specific shape
- active site complementary to substrate
- enzyme only catalyses specific reaction
What does it mean if an enzyme’s denatured?
- bonds that maintain enzyme’s tertiary structure break
- this causes the active site to change shape which means it’s no longer complementary to the substrate
- therefore E-S complexes can no longer form
What can cause enzymes to denature?
- temp (too high)
- pH (too high/low)
- mutation in gene that codes for protein (primary structure altered)
- non-competitive inhibitor
What are the factors that affect enzyme activity?
- temp
- pH
- substrate conc
- enzyme conc
- presence of a competitive inhibitor
- presence of a non-competitive inhibitor
How does temp affect enzyme activity?
- as temp increases, enzyme activity increases due to an increase in kinetic energy which results in more frequent and successful collisions
- enzyme activity increases up until optimum temp
- after optimum temp, enzyme activity decreases as the bonds that maintain enzyme’s tertiary structure break which causes the active site to change shape which means it’s no longer complementary to the substrate therefore E-S complexes can no longer form (enzyme denatured)
How does pH affect enzyme activity?
- all enzymes have an optimum pH
- above/below the optimum pH, H^+ and OH^- ions found in acids and alkalis can disrupt ionic bonds and H bonds that maintain the enzyme’s tertiary structure which causes the shape of the active site to change (enzyme denatured)
How does substrate conc affect enzyme activity?
- the higher the substrate conc, the higher the enzyme activity
- initially, more substrate molecules = more frequent collisions between enzymes and substrates
- however after the saturation point, all active sites are occupied and increasing substrate conc makes no difference
How does enzyme conc affect enzyme activity?
- the higher the enzyme conc, the higher the enzyme activity
- more enzyme molecules = more frequent collisions between enzyme and substrate
- however if substrate conc is limited, increasing conc of enzyme will have no effect
How do competitive inhibitors affect enzyme activity?
- competitive inhibitor molecules have similar shapes to substrate molecules
- they compete with substrate molecules by binding to the enzyme’s active site
- how much of the enzyme is inhibited depends on the concs of the inhibitor and substrate molecules (high conc of inhibitor means that hardly any of the substrate molecules can bind to the enzymes whereas high substrate conc would mean that substrate molecules have a higher chance of reaching the enzyme molecules before the inhibitor conc increases)
