2.5 enzymes

Question 1

define enzyme and substrate

Answer 1

enzyme: a globular protein that speeds up the rate of a chemical reaction by lowering the activation energy (a biological catalyst)

substrate: a compound that binds to an enzyme’s active site and is converted into a product (the substrate is complementary in shape and chemical properties to the active site)

Question 2

outline the steps in enzymatic binding and catalytic activity with the aid in f the following diagram

Answer 2

1. enzyme and substrate collide in an appropriate orientation (substrate binds to the enzyme’s active site)
2. enzyme and substrate form a complex, leading to catalysis (enzyme-substrate interaction shows specificity)
3. substrate is converted into a product (enzyme may stress the bonds within the substrate to catalyse this process)
4. enzyme and product dissociate (enzyme is not consumed by the reaction and may be re-used)

Question 3

identify factors that can affect an enzyme’s molecular motion and collision with a substrate

Answer 3

temperature- increases the kendrick energy of particles, leading to more frequent collisions

substrate concentration- increases frequency of collisions with enzyme

enzyme concentration- increases fréquence of collision with substrate

Question 4

distinguish between the mock and the key and induced fit models of enzyme specificity

Answer 4

L and K model:
substrate and active site are complementary in both shape and chemical properties

means that enzymes are specific for the reaction they catalyse

induced fit model:
active site is not a perfect fit, but undergoes a conformational change in shape to accommodate substrate

this stresses bonds in the substrate (promoting catalysis) and gives rise to broad specificity

Question 5

explain the effect of different factors on enzyme activity

Answer 5

temperature:
-at low temperatures there is insufficient activation energy for reaction to proceed
-as temperature increases the rate of reaction increases (higher kinetic energy-more collisions)
-at a certain optimum temperature, the rate of reaction will plateau (peak efficiency)
-above this temperature, the enzyme will begin to denature and rate of reaction will decrease

pH:
-enzymes have an optimal pH at which the rate of reaction is the highest
-at higher and lower pH levels, activity will decrease (leading to a bell shaped curve)
-this is because the pH affects the charge and solubility of the enzyme
-the change in the enzyme’s chemical properties causes it to denature (loss tertiary structure)

substrate concentration:
-enzyme activity increases as substrate concentration increases
-this is because there are more substrate particles, leading to a higher rate of successful collisions
-at a certain point, the rate of enzyme activity will plateau
-this is because all enzyme active sites are occupied (the solution is saturated)

Question 6

explain the benefits of immobilized enzymes in industry, with examples

Answer 6

immobilized enzymes have been fixed to a static surface in order to increase enzyme efficiency

enzyme concentrations are conserved, as the enzyme is not dissolved - hence it can be re-used

product is more easily separated from enzyme, as the enzyme is fixed in position

examples of mobilized enzymes in industry include in food production, medicine and biofuel production

Question 7

outline the production of lactose-free milk and it’s advantages

Answer 7

lactose is fixed to agarose beads (lactose purified from yeast or bacteria)

milk is passed over the immobilized enzyme, becoming lactose free

advantages:
-provided a source of milk and other diary products for lactose-intolerant individuals
-increases sweetness in the absence of artificial sweeteners (monosaccharides are sweeter in taste)
-reduces the crystallization of ice creams (monosaccharides are more soluble, less likely to crystallize)

Question 8

suggest ways of measuring the following enzyme-catalyzed reactions

Answer 8

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