biomolecule tests Flashcards
what is the test for starch?
iodine test
test for starch
- add a few drops of iodine to the sample
- iodide ions react with the centre of starch molecules
- turns blue black in presence of starch
what is the test for reducing sugars?
benedicts test
test for reducing sugars
- benedicts test
- add blue benedicts reagent to a sample solution
- heat in water bath
- brick red precipitate forms if reducing sugar is present
test for non-reducing sugars
- after negative result for reducing sugar (stays blue)
- add acid and boil
- wait to cool and add alkali to neutralise
- add benedict’s solution
- positive test : colour change from blue to green/yellow/orange/red
what is the test for proteins?
biuret test
test for proteins
- add biuret solution at 45 degree angle to form a layer.
- observe colour change, gently mix and observe again.
- if turns violet indicates presence of protein
what is the test for lipids?
emulsion test
test for lipids
- emulsion test
- dissolve the sample in ethanol by adding ethanol and shaking
- add distilled water
- positive test : white emulsion forms
explain the reason for the colour change in the benedicts test
copper sulphate being reduced by copper oxide
explain the colour change in the iodine test
due to the starch being digested by enzymes
explain the precipitation formation in the emulsion test
lipids dissolve in non polar substances but not polar substances like water
risk assessment of biomolecule tests
biuret reagent - dont dispose down sink
ethanol - dont use near naked flame
colorimeter method
- to get quantitative answers
- set filter
- calibrate
- insert samples
- create calibration curve
biosensors
- strand of DNA or protein is immobilised
- sample will bind to immobilised DNA/protein
- binding causes change in a transducer
- current determines concentration of sample
serial dillution
- 5 test tubes
- each contain a known concentration
- each test tube is of equal volume
- each tube has a concentration decrease of the same amount each time
- e.g. tube 1 = 10cm3 solution
tube 2 = 8cm3 solution, 2cm3 water
tube 3 = 6cm3 solution, 4cm3 water
what is the purpose of a control test tube? (2)
it acts as a blank. this is to show the impact of the manipulation of the IV in comparison to without.
how can reliability of experiments be improved (2)
- repeat
- sample each test tube twice
describe how a student could carry out a chemical test for reducing sugar and suggest how they can estimate the amount of reducing sugar in a sample (5)
- add benedicts reagent and observe any colour change
- colour change will be blue to brick red
- compare the colour with that of a known solution
- mass of precipitate formed reflects concentration
chromatography of a protein
- separate mixtures
- mobile phase flows through the stationary phase
- carries the components of the mixture with it
how to measure Rf value
distance travelled by compound ÷ distance travelled by solvent = Rf
risk assessment/evaluation of chromatography of protein
- plates from compromised powder, dont chip with pencil
- waft the plate to dry, don’t blow as spit has proteins
- no fingers on plate
