2.5: Enzymes

Question 1

enzyme definition

Answer 1

A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold without being used up themselves (i.e. a biological catalyst)

Question 2

substrate definition

Answer 2

reactant in a biochemical reaction

Question 3

active site

Answer 3

region where substrate binds to enzyme and catalyses the reaction

Question 4

lock and key hypothesis

Answer 4

will only react if:
structurally: 3d structure matches perfectly
chemically: chemically attracted to each other

Question 5

why lock and key hypothesis is not true

Answer 5

means only one type of reaction can be formed by each enzyme but in reality more than one can occur

Question 6

induced fit model

Answer 6

enzymes can catalyse multiple reactions
- when substrate approaches enzyme, induced conformational chnage in active site
- stress on substrate from this reduces activation energy of reaction
- enzyme reverts to original shape when substrate is released

Question 7

collision

Answer 7

coming togetehr of substrate molecule and active site

Question 8

random motion

Answer 8

when molecules are dissolved in water, each molecule is speratelt moving

Question 9

collisions ar ethe result of

Answer 9

random movemtns of both substrate and enzyme

Question 10

successful collisions

Answer 10

occur only when substrate and active site are aligned correctly

Question 11

immobolized enzymes definition

Answer 11

are those that are attached to a material so that it stays in place

Question 12

how do immobollized enzymes stay in place

Answer 12

• Bound to solid or porous materials
• Mixed in with a matrix
• Embedded in a soluble membrane
• Aggregations of enzymes bonded together
• Attached to surfaces, e.g. glass
• Entrapped in gels, e.g. alginate gel beads

Question 12

examples of immobolized enzymes

Answer 12

• carbon capturing: polluted air is passed over enzymes, which traps CO2 for storage, reduces emissions from factories
• detergents: proteases and lipases to help breakdown protein and fat stains

Question 13

Advantages of enzyme immobilization:

Answer 13

• Concentration of substrate can be increased as the enzyme is not dissolved
• Recycled enzymes can be used many times, immobilized enzymes are easy to separate from the reaction mixture, resulting in a cost saving
• Separation of the products is straight forward (this also means that the reaction can stopped at the correct time).
• Stability of the enzyme to changes in temperature and pH is increased reducing the rate of degradation, again resulting in a cost saving.

Question 14

lactose intolerance?

Answer 14

not having enouhg lactase enzymes, can cause allergies

Question 15

production of lactose free milk

Answer 15

• Lactase obtained from commonly from yeast
• Lactase is bound to the surface of alginate beads
• Milk is passed (repeatedly) over the beads
• The lactose is broken down into glucose and galactose
• The immobilized enzyme remains to be used again many times

Question 16

Other uses of lactose free milk?

Answer 16

• sweetness of milk (glucose and galactose are sweeter in flavour)
• reducing the crystallisation of ice-creams (glucose and galactose are more soluble than lactose)
• shortening the production time for yogurts or cheese (bacteria ferment glucose and galactose more readily than lactose)

Question 17

Denaturation of proteins?

Answer 17

three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of amino acids within the molecule are relatively weak and they can be disrupted or broken
- results in a change to the conformation of the protein, called denaturation
- does not normally return to its former structure – the denaturation is permanent. Soluble proteins often become insoluble and form a precipitate

Question 18

causes of denaturation?

Answer 18

• Heat can cause denaturation: vibrations within the molecule breaks intramolecular bonds or interactions.
• Extremes of pH can cause denaturation: charges on R groups are changed, breaking ionic bonds within the protein or causing new ionic bonds to form.

Question 19

denaturation of enzymes causes?

Answer 19

• change in structure means a change in the active site. If the active site changes shape the substrate is no longer able to bind to it

Question 20

effect on temperature on enzyme activity

Answer 20

• Low temperatures result in insufficient thermal energy (lower activity)
• Increasing the temperature will increase the speed and motion of both enzyme and substrate (higher activity)
• optimal temperature: the rate of enzyme activity will be at its peak
• Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the hydrogen bonds holding the enzyme together (could also denaturize)

Question 21

effect of pH on the rate of enzyme activity

Answer 21

• pH alters the charges on the active site of an enzyme and the surface of the substrate
• This can reduce the ability of both molecules to bind to each other
• optimum pH (peak), moving outside of this range (diminished rate of reaction)
• normally reversible when environment returns to optimal pH (ionic charges on active site are restored and enzyme can resume normal function)

Question 22

effect of substrate concentration on enzyme activity

Answer 22

• rate of an enzyme catalyzed reaction increases in direct proportion to the substrate concentration until the reaction reaches a maximum rate
• not enough enzymes (enzymes become limiting factor) causes more competition for active sites, maximum efficiency, enzymes are saturated beyond here
• graph logs

Question 23

effect of ENZYME concentration on enzyme activity

Answer 23

• enzyme concentration is increased, the rate of the enzyme
• assuming there is always excess of substrate, it is directly proportional
• linear positive graph
• substrate becomes limiting factor if not excess, becomes beyond the max rate of reaction