topic 2.5- enzymes

Question 1

what are enzymes?

Answer 1

globular proteins that work as biological catalysts, speeding up chemical reactions without being altered themselves

Question 2

explain enzyme-substrate specificity

Answer 2

the shape and chemical properties of the active site and the substrate match each other- this allows the substrate to bind, but not other substances

Question 3

what does enzyme catalysis involve?

Answer 3

molecular motion and the collision of substrates with the active site

Question 4

state the 3 stages of enzyme catalysis

Answer 4

• the substrate collides with and binds to the active site of the enzyme.
• while substrates are bound to the active site they change into different chemical substances (=the products)
• the products separate from the active site, leaving it vacant for substrates to bind again

Question 5

define a successful collision between an enzyme and a substrate

Answer 5

collisions in which the substrate and the active site are correctly aligned to allow binding to take place

Question 6

give 3 factors that affect the rate of activity of enzymes

Answer 6

1. temperature
2. pH
3. substrate concentration

Question 7

how does temperature affect enzyme activity?

Answer 7

• higher KE; enzymes and substrates move around faster -> increased frequency of collisions between substrate and active site
• when enzymes are heated, bonds in the enzyme vibrate more and the chance of the bonds breaking increases, meaning the shape of the enzyme and its active site changes (= denaturation)

Question 8

how does pH affect enzyme activity?

Answer 8

most enzymes have an optimum pH- at either side of this pH, the structure of the enzyme is altered, including the active site. beyond a certain pH, denaturation occurs

Question 9

how does substrate concentration affect enzyme activity?

Answer 9

• if conc of substrates increases, substrate-active site collisions will take place more frequently and the rate of reaction will increase
• however, as it rises, more and more of the active sites are occupied at any moment, meaning a greater proportion of substrate-active site collisions will be blocked- plateaus.

Question 10

what happens during enzyme denaturation?

Answer 10

the active site is altered so the substrate can no longer bind (enzyme may also become insoluble)

Question 11

what does catalase do?

Answer 11

catalyses the conversion of hydrogen peroxide into oxygen and water

Question 12

define enzyme immobilisation

Answer 12

the attachment of enzymes to another material or into aggregations, so that the movement of the enzyme is restricted, but in such a way that it retains its full activity or most of its activity.

Question 13

state 3 ways in which an enzyme could be immobilised

Answer 13

• attaching the enzymes to a glass surface
• trapping the enzymes in an alginate gel
• bonding enzymes together to form enzyme aggregates

Question 14

state 4 advantages of immobilising enzymes

Answer 14

• enzyme can easily be separated from the products of the reaction; reaction stopped at ideal time and products not contaminated
• enzymes retrieved from reaction mixture and can be reused; saves costs
• increases stability of enzymes to changes in temperature and pH, reducing the rate at which they are degraded and have to be replaced
• substrates can be exposed to higher enzyme concentrations than with dissolved enzymes, speeding up ROR

Question 15

how is lactose free milk produced?

Answer 15

lactose —(lactase)–> b glucose + galactose

Question 16

give 4 advantages of lactose free milk

Answer 16

• some people are lactose intolerant
• galactose and glucose are sweeter than lactose, so less sugar needs to be added to sweet foods containing milk
• lactose tends to crystallise during ice cream production, giving a gritty texture- glucose and galactose are more soluble so they remain dissolved, giving a smoother texture
• bacteria ferment glucose and galactose faster than lactose, so the production of yoghurt/cottage cheese is quicker