required practical 1

Question 1

what is required practical one

Answer 1

investigation into the effect of a named variable on the rate of an enzyme-controlled reaction

Question 2

what influences rate of reaction of an enzyme controlled reaction is influenced

Answer 2

• temperature
• pH
• concentration of the substrate
• concentration of enzyme

the effect of each can be determined by changing a single variable and measuring its effect on the reaction

important to keep all other variables constant - so does not influence the results

Question 3

practical 1 equipment list

Answer 3

powdered milk suspension

trypsin solution - 0.5%

distilled water

hydrochloric acid - 0.1M

5cm^3 syringes

flat bottomed tubes

water bath

timer

Question 4

practical 1 method - control sample

Answer 4

make two control samples

• take two flat bottomed tubes
• add 5cm^3 of milk suspension to each tube
• add 5cm^3 of distilled water to one tube- this control will indicate the absence of enzyme activity
• add 5cm^3 of hydrochloric acid to the other - this control indicates the colour of a completely hydrolysed sample

Question 5

practical 1 method - main experiment

Answer 5

take 3 test tubes and add 5cm3 of milk to each - place in water bath at 10C for 5 minutes to equilibrate

add 5cm3 trypsin to each and start timer

record how long it takes for the milk samples to completely hydrolyse and become colourless

repeat steps at 20C, 30C, 40C and 50C

find the mean time for the milk to be hydrolysed at each temperature and use this to work out for the rate of reaction

rate of reaction = 1 / mean time

Question 6

practical 1 risks

Answer 6

broken glass - cuts

hydrochloric acid - irritation

hot liquids - scalding

enzymes - allergies

Question 7

practical 1 - results and conclusions

Answer 7

plot a graph of rate of reaction against temperature
(temp on bottom as IV)

• milk contains a protein called casein which, when broke down causes the milk to turn ​colourless​​. ​Trypsin​​ is a​ protease enzyme​​ which ​hydrolyses the casein protein
• the temperature increases from 10°C,​ kinetic energy increases​​ so more enzyme-substrate complexes ​​form. This means that the rate of reaction increases​​ up to the optimum temperature
• temperatures beyond the optimum, ​bonds​​ in the enzyme ​tertiary structure break​​, which changes the shape of the​ active site​​. This means that the substrate and enzyme are no longer ​complementary​​