2.5 Enzymes

Question 1

what is an enzyme?

Answer 1

a globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction

Question 2

why can enzymes be reused?

Answer 2

they are not changed or consumed by the reaction they ctatlyse

Question 3

what is the active site?

Answer 3

the region on the surface of the enzyme which binds to the substrate molecule

Question 4

what do the active site and the substrate have? (2)

Answer 4

they complement each other in terms of both shape and chemical properties
- only specific substrate is capable of binding to a particular enzyme active site

Question 5

what are 2 consequences of enzymes reactions typically occurring in aqueous solutions?

Answer 5

• the substrate and enzyme are usually moving randomly within the solutions (Brownian motion)
• sometimes an enzyme may be fixed in positions (eg. membrane-bound) this serves to localise reactions to particular sites

Question 6

what occurs in enzyme catalysis?

Answer 6

requires that the substrate be brought unto close physical proximity with the active site
- when a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed
- the enzyme catalyses the conversion of the substrate into product, creating an enzyme-product complex
- the enzyme and product then disassociates- as te enzyme was not consumes (it can continue to catalyse further)

Question 7

how can collision frequency increase enzyme catalysis? (2)

Answer 7

• increasing the molecular motion of the particles (thermal energy can be introduced to increase kinetic energy)
• increasing the concentration of particles (either substrate or enzyme concentrations)

Question 8

what is the indentation or cavity in which the substrate can bind with high specificity called?

Answer 8

active site

Question 9

what are the shape and chemical properties of the active site dependent on?

Answer 9

the tertiary structure of the enzyme

Question 10

how do high temperatures and extreme pHs modify the enzyme structure? (2)

Answer 10

• these factors disrupt the chemical bonds which are necessary to maintain the tertiary structure of the enzyme
• any change to the structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate

Question 11

how does temperature affect the rate of activity of the enzyme? (6)

Answer 11

• low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed
• increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity
• because higher kinetic energy will result in more frequent collisions between enzymes and substrates
• at an 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 enzyme’s hydrogen bonds
• this causes the enzyme (particularly the active site) to lose its shape resulting in the loss of activity (denaturation)

Question 12

what is the effect of pH on enzyme activity? (3)

Answer 12

• changing the pH will alter the charge of the enzyme, which will alter protein solubility and overall shape
• changing shape or charge of the active site will diminish its ability to bind the substrate abrogating enzyme function
• enzymes have an optimal pH and moving outside this range diminished enzyme activity

Question 13

how effect does substrate concentration have on substrate specificity? (4)

Answer 13

• increasing substrate concentration will increase the activity of a corresponding enzyme
• more substrate means there is an increased chance of enzymes and substrate colliding and reacting within a given period
• after a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels
• this is because the environment is saturated and all enzymes are bound and reacting

Question 14

using what two ways can you measure enzyme activity?

Answer 14

• the amount/rate of substrate decomposition
• the amount/rate of product formation

Question 15

what are the main factors which will affect the activity of an enzyme on a given substrate that you can use for an experiment? (4)

Answer 15

• temperature (use water bath to minimise fluctuations)
• pH (acidic or alkaline)
• substrate concentration (choose range to avoid saturation)
• presence of inhibitor (type of inhibitor will be enzyme-specific)

Question 16

why are immobilised enzymes field to a static surface to improve the efficiency of the catalysed reaction? (2)

Answer 16

• enzyme concentrations are conserved as the enzyme is not dissolved - hence it can be retained for reuse
• separation of the product is more easily achieved as the enzyme remains attached to the static surface

Question 17

what 5 industrial practices are immobilised enzymes used in?

Answer 17

biofuels - enzymes used t breakdown carbohydrates to produce ethanol-based fuels
medicine - enzymes are used to identify a range of conditions, including certain diseases and pregnancy
biotechnology - enzymes are involved in a number of processes including gene splicing
food production - enzymes are used in the production and refinement of beer and dairy products
- textiles - enzymes are used in processing fibres

Question 18

what is lactose?

Answer 18

lactose is a disaccharide of glucose and galactose which can be broken down by enzyme lactase

Question 19

how can lactose-free milk be produced? (2)

Answer 19

• lactase is purified from yeast or bacteria and bound to inert substances (eg alginate beads)
• milk is then repeatedly passed over the immobilised enzyme becoming lactose-free

Question 20

how are scientists trying to create transgenic cows which produce lactose-free milk?

Answer 20

• involves splicing the lactase gene in cow’s genome so the lactose is broken down prior to drinking

Question 21

what are 4 advantages of lactose-free milk?

Answer 21

• as a source of dairy for lactose-intolerant individuals
• means of increasing sweetness in absence of artificial sweeteners (as monosaccharides are sweeter tasting)
• as a way of reducing crystallisation of icecream (monosaccharides are more soluble, less likely to crystalise)
• as a means of reducing production time for cheeses and yoghurts (bacteria ferment monosaccharides more readily)