enzymes

Question 1

definition of a catalyst?

Answer 1

a chemical which increases the rate of reaction without being used up itself in the reaction

Question 2

2.10 enzymes are __________ __________

Answer 2

biological catalysts

Question 3

true or false: catalysts change after a reaction and so can’t catalyse more reactions

Answer 3

false

Question 4

explain the lock and key theory for how enzymes work

Answer 4

• substrate & enzyme collide
• substrate binds to active site of enzyme
• binding to active site strains chemical bonds in substrate molecules & so the reaction occurs by an alternative pathway with a lower activation energy
• once reaction occurred, products don’t fit active site’s shape as well as substrates did, so they’re released
• after reaction, enzyme molecule free to catalyse next reaction

Question 5

why can each enzyme only catalyse one reaction?

Answer 5

because active site of a particular enzyme has a specific shape which is complementary to the shape of the substrate(s)

Question 6

2.11 understand how temperature changes can affect enzyme function, including changes to the shape of active site

Answer 6

• all proteins held together by forces between diff. parts of amino acid chain
• high temps & changes of pH disrupt these forces, so shape changes
  –> protein denatured
  –> in enzymes, active site changes shape so no longer complementary to substrate

Question 7

2.12 practical: investigate how enzyme activity can be affected by changes in temperature

Answer 7

• add 5cm³ starch solution to test tube & heat to a set temp using beaker of water w Bunsen burner
• add drop of iodine to each of the wells of a spotting tile
• use syringe to add 2cm³ amylase to the starch solution and mix well
• every minute, transfer a droplet of solution to a new well of iodine solution (which should turn blue-black)
• repeat this transfer process until the iodine solution stops turning blue-black (this means the amylase has broken down all the starch)
• record time taken for the reaction to be completed
• repeat the investigation for a range of temperatures (from 20°C to 60°C)

Question 8

2.13 understand how enzyme function can be affected by changes in pH altering the active site

Answer 8

• if pH too high/low, bonds that hold amino acid chain together to make up protein disrupted/destroyed
• this’ll change shape of active site, so substrate can’t fit into it, reducing rate of activity
• moving too far away from optimum pH will cause enzyme to denature & activity will stop

Question 9

2.14B practical: investigate how enzyme activity can be affected by changes in pH

Answer 9

• add drop of iodine to each of the wells of a spotting tile
• use syringe to place 2 cm³ of amylase into a test tube
• add 1cm³ of buffer solution (at pH 2) to test tube using syringe
• use another test tube to add 2 cm³ of starch solution to amylase & buffer solution, start stopwatch whilst mixing using a pipette
• every 10 seconds, transfer a droplet of the solution to a new well of iodine solution (which should turn blue-black)
• repeat this transfer process every 10 seconds until the iodine solution stops turning blue-black (this means the amylase has broken down all the starch)
• record time taken for reaction to be completed
• repeat investigation w buffers at different pH values (ranging from pH 3.0 to pH 7.0)