2.5 Enzymes

Question 1

Enzyme

Answer 1

• A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold (i.e. a biological catalyst)

Question 2

Active Site

Answer 2

• Region on the surface of an enzyme to which the substrates bind and which catalyzes the reaction.

Question 3

Substrates

Answer 3

• Substances that enzymes convert into products in these reactions (the reactants).

Question 4

Products

Answer 4

• The end result.

Question 5

Lock and Key model

Answer 5

• The first theory of the action of an enzyme binding to a substrate.

Question 6

Induced Fit Model

Answer 6

-The current theory of the action of an enzyme binding to a substrate.

Question 7

Enzyme-substrate specificity

Answer 7

• A feature of an enzyme activity with regard to the kind of substrate reacting with an enzyme to yield a product.

Question 8

State what is meant by the term collision in enzyme catalysis.

Answer 8

• The coming together of a substrate molecule and an active site is known as a collision.

Question 9

Explain why not all collisions between enzymes and substrates result in catalysis.

Answer 9

• As not all collisions result in binding.

Question 10

Explain why the presence of water is critical for most enzyme reactions.

Answer 10

• Most enzyme reactions occur when the substrates are dissolved in water.
• All molecules dissolved in water are in random motion, with each molecule moving separately.

Question 11

Enzymes can be immobilized (e.g. embedded in cell membranes). Enzymes can also be free to move, but they tend to move more slowly than substrates, explain why.

Answer 11

• If not immobilized the enzyme can move too, however enzymes tend be larger than the substrate(s) and therefore move more slowly.

Question 12

• Effects of Temperature on Rate of Reaction

Answer 12

• Low temperatures result in insufficient thermal energy for the activation of a given enzyme-catalysed reaction to be achieved.
• Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity.
• This is because a higher kinetic energy will result in more frequent collisions between enzyme and substrate.
• At an optimal temperature (may differ for different enzymes), 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.
• This causes the enzyme (particularly the active site) to lose its shape, resulting in a loss of enzyme activity (denaturation).

Question 13

Effects of pH on Rate of Reaction

Answer 13

• Changing the pH will alter the charge of the enzyme, which in turn will protein solubility and may change the shape of the molecule.
• Changing the shape or charge of the active site will diminish its ability to bind to the substrate, halting enzyme function.
• Enzymes have an optimum pH and moving outside of this range will always result in a diminished rate of reaction.
• Different enzymes may have a different optimum pH ranges.

Question 14

Effects of Substrate Concentration on Rate of Reaction

Answer 14

• Increasing Substrate Concentration increases Rate of Reaction.
• At optimum concentration of substrate molecules, all active sites are full and working at maximum efficiency.
• Any increase in concentration beyond the optimum, will have no added effect as there are no extra active sites to be used.

Question 15

List eight common uses of enzymes in industry.

Answer 15

• Detergents.
• Food Industry.
• Paper production.
• Textiles.
• Brewing.
• Medicine & Biotechnology.
• Biofuels.

Question 16

Enzymes used in industry are commonly immobilised.

Describe the advantages of immobilising enzymes.

Answer 16

• Concentration of substrate can be increased as the enzyme is not dissolved - this increases the rate of reaction.
• 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 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 17

List three ways in which enzymes can be immobilised.

Answer 17

• Enzymes used in industry are usually immobilized. They are attached to a material so that their movement is restricted. Common ways of doing this are:
• Aggregations of enzymes bonded together.
• Attached to surfaces, e.g. glass.
• Entrapped in gels, e.g. alginate gel bead.

Question 18

Outline the process by which lactose-free milk is produced by immobilized enzymes.

Answer 18

Production of Lactose-free milk:

• Lactase obtained from commonly from yeast (bacteria is an alternative).
• 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 and does not affect the quality of the lactose free milk.

Question 19

State the three other commercial reasons that lactose free milk is produced.

Answer 19

• As a means to increase the sweetness of milk (glucose and galactose are sweeter in flavour), thus negating the need for artificial sweeteners.
• As a way of reducing the crystallisation of ice-creams (glucose and galactose are more soluble than lactose).
• As a means of shortening the production time for yogurts or cheese (bacteria ferment glucose and galactose more readily than lactose).