the final battle part 3 Flashcards
how is a benedicts test for reducing sugars carried out
1) place the sample to be tested in a boiling tube and grind up or blend it with water
2) add same volume of benedicts reagent
3) heat the mixture gently in a boiling water bath for 5 mins
how does the benedicts test work
reducing sugars will react with copper ions in Ben.Reagent
this will cause the addition of electrons to the blue Cu2+ ions reducing them to brick red Cu+ ions
the more precipitate formed, the more reducing sugars present and less blue Cu2+ ions left in
qualitative
non-reducing sugars dont react with benedict reagent so it remains blue eg) sucrose
however if sucrose boiled with dilute hydrochloric acid it gives positive result as sucrose has been hydrolysed by acid to glucose and fructose which are both reducing sugars
how is starch tested for
a few drops of iodine dissolved in potassium iodide mixed with sample. if goes black starch present
how are reagent strips used
used to determine the concentration of reducing sugars
what is colorometry
a quantitative method measuring absorbanceor trasmission of light by coloured solution
how is a colorometer callibrated
using distilled water
Slide the Colorimeter lid closed. Press the CAL button on the Colorimeter to begin the calibration process. Release the CAL button when the red LED begins to flash. When the red LED stops flashing, the calibration is complete.
why is a colorometer callibrated
Like with any piece of equipment or machinery, color measurement instruments need maintenance to assure that they continue to work correctly and with a predictably high degree of accuracy. Calibration allows us to set a baseline for the instrument and make sure that the baseline is maintained over time.
what are biosensors
another quanitative method used to determine the concentration of molecules like glucose
analyte is the compound under investigation
Moleculuar recognition- protein immobilised to surface or a single strand of DNA, on eg a glucose test strip which will interact and bind to molecule inquestion
Transduction- interaction causes a change in the transducer which detects changes in eg pH and responds by release of immobilised dye on test strip or electric current in glucose testing machine
Display-this then produces a visible qualitative or quantitative signal such as a colour on a test strip or reading machine
how is an emulsion test for lipids carried out
sample mixed with ethanol and resulting solution is mixed with water and shaken. if white emulsion forms as a layer on top of solution it indicates presence of a lipid but if clear is negative
how is a biuret test carried out
- set concentration of lipid sample mixed with equal volume of 10% sodium hydroxide
- copper sulfate solution added a few drops at a time until solution blue
- solution mixed and left for 5 mins
Yellow-orange = negative Purple-black = positive
thin layer chromatography how is it carried out
- handle plate by edges and draw pencil line 2cm from bottom of plate
- put amino acid solution on the line spaced out and allow to dry then do again
- then on rest of line put know solutions of amino acids
- place into jar containing solvent and close lid as fumes dangerous
- leave until solvent has reached 2cm from top and take out and draw pencil line along solvent front
- spray with ninhydrin spray in fume cupboard
what are the 2 phases of TLC
stationary phase- silaca gel used
mobile phase- organic solvent
what does the rate that different amino acids move through silaca gel in organic solvent depend on
interactions (hydrogen bonds)
and solubility in mobile phase (organic solvent)
how is the Rf value calculated
dist. moved by solute/ dist. moved by solvent
how is DNA extracted
> grind sample in pestle and mortar to break down cell walls]
mix sample with detergent to break down cell membrane and release cell contents into solution
add salt to break hydrogen bonds between DNA and water molecules
add protease enzyme to break down proteins asssoicated with DNA in the nuclei
add layer of ethanol to cause DNA to precipitate out of the solution
pick out DNA strands with rod
