(U1) Enzymes Flashcards
What are the stages in enzyme action? (4)
- substrate attaches to active site
- enzyme-substrate complex formed
- enzyme-product complex formed
- products leave active site separately
What are the 2 forms of metabolic reaction?
- catabolism (cut)
- anabolism (add)
What is activation energy? (2)
- the minimum amount of energy
- required for a reaction to occur
Why does high and low pH affect enzyme active sites? (2)
- active sites have their shape due to bonds in tertiary protein structure
- changes to pH affect ionic bonds, thus changing the shape of the active site
How does an enzyme actually breakdown a substrate? (3)
- enzyme puts pressure on bonds in the substrate
- weakens bonds
- bonds break
Explain the lock and key model (2)
- enzyme has an exactly complementary active site to the substrate
- collisions between the two result in an enzyme-substrate complex
Explain the induced fit model (4)
- enzyme active site not totally complementary to substrate
- active site undergoes a conformational change in shape
- active site now precisely fits the substrate
- enzyme-substrate complexes now form on collisions with the substrate
What is the effect of increasing substrate concentration on enzyme activity? (4)
- enzyme activity increases, then levels off
- greater concentration increases chance of collisions between active sites and substrates
- therefore more enzyme-substrate complexes are formed
- at high conc, enzyme concentration becomes limiting - all active sites occupied
What is the point at which the substrate concentration / enzyme activity graph levels off at called?
Point of saturation
What is the effect of increasing enzyme concentration on enzyme activity? (5)
- enzyme activity increases, but can level off
- greater concentration increases chance of collisions between active sites and substrates
- therefore more enzyme-substrate complexes are formed
- at high conc, substrate concentration can become limiting - all active sites occupied
- if in excess, the trend just continues - increasing activity
What is the effect of changing pH on enzyme activity? (4)
- deviation from optimum causes decrease in enzyme activity
- ionic bonds in tertiary structure of enzyme disrupted
- active site undergoes a conformational change in shape - becomes denatured
- less enzyme-substrate complexes formed on collisions with substrates
What is the effect of increasing temperature on enzyme activity? (5)
- increasing temperature increases enzyme activity until a point where activity dramatically declines
- increases due to increased kinetic energy
- increases chance of collisions between substrates and active sites - forming enzyme-substrate complexes
- high temps, hydrogen bonds broken in tertiary structure of the enzyme, causing a conformational change in shape of active site (denaturation)
- active site no longer complementary - no more enzyme-substrate complexes formed
What are the advantages of using enzyme immobilisation in industry? (4)
- production can occur continuously
- product is enzyme free, reducing purification costs
- enzymes easily reused
- stability of enzyme improved: active over greater range of pH and temps (thermostable)
What are the 5 methods of immobilisation?
- absorption onto an inert support (e.g. collagen matrix)
- covalent bonding onto a solid support (e.g. cellulose fibres)
- cross-linking via a binding chemical (e.g. glutaraldehyde)
- encapsulation in a semi-permeable membrane (e.g. nylon)
- entrapment inside a gel (e.g. silica gel)
Where are enzymes used in industry?
in terms of machinery
Flow-column reactors
What are the advantages and disadvantages of absorption immobilisation? (4)
(enzymes)
Advantages:
- easy to immobilise, therefore cheap
- no gel barrier diffusion neccessary
Disadvantages:
- enzymes easily washed away - unreliable
- active sites may be made inaccessible (blocked by material)
What are the advantages and disadvantages of covalent bonding immobilisation? (7)
(enzymes)
Advantages:
- enzymes not washed away - reliable
- resistant to pH and temp changes
- active sites must be exposed
Disadvantages:
- relatively expensive
- active sites may be made inaccessible (blocked by material)
- long term regeneration of enzyme is impossible
- high activity can’t be obtained
Most widely used method
What are the advantages and disadvantages of cross-linking immobilisation? (7)
(enzymes)
Advantages:
- enzymes not washed away - reliable
- resistant to pH and temp changes
- active sites must be exposed
Disadvantages:
- relatively expensive
- active sites may be made inaccessible (blocked by material)
- long term regeneration of enzyme is impossible
- high activity can’t be obtained
What are the advantages and disadvantages of encapsulation immobilisation? (3)
(enzymes)
Advantages:
- active sites must be exposed - activity not adversely affected
Disadvantages:
- diffusion of substrate across matrix reduces rate of activity
- some enzymes “leak out”
What are the advantages and disadvantages of entrapment immobilisation? (4)
(enzymes)
Advantages:
- active sites exposed - reliable - activity not adversely affected
- enzymes can’t “leak out”
Disadvantages:
- slow diffusion across matrix reduces rate of activity
- slow diffusion of products out of matrix
What is a cofactor that allows an enzyme to function effectively called?
An activator
What do cofactors do? (2)
- Attach to an enzyme’s active site or elsewhere
- influencing the shape of the enzyme or participating in enzymatic reactions
What are the differences between cofactors and coenzymes? (2)
- cofactors are non-protein (prosthetic groups), coenzymes are organic molecules
- coenzymes are temporary, cofactors can be permanent
What are the 2 types of inhibitor?
What do each mean?
- competitive: resembles the shape of substrate:
- competes for the active site
- Doesn’t remain permanently
- non-competitive: doesn’t resemble the shape of the substrate, either:
- Binds temporarily to allosteric site, temporary change in shape
- Binds permanently to allosteric site, 3D conformational change in shape
