tests for biological molecules Flashcards
what does qualitative results refer to with biochemical tests
is the substance present or absent
what does semi qualitative refer to
how much is present
what are some reducing sugars
all monosaccharides plusmaltose and lactose
galactose
glucose
fructose
maltose
what are some non reducing sugars
sucrose which is the only one i need to know. it is a disaccharide
what is the method for the benedicts rest for reducing sugars
add a fixed volume (2cm3) to the sample into a test tube.
add equal amount of benedicts reagent
boil for 5 mins in a water bath
what are the results for the benedicts test for reducing sugars
negative: the solution will remain blue
positive: will turn from blue to green then yellow, brown, brick red , red depending on the concentration
what is the principal of the benedicts test for reducing sugars
when they are heated in the presence of an alkali they get converted to enediols.
the copper 2 ions are reduced to copper 1 ions which causes the colour change
method for the modified benedicts test for non reducing sugars
add equal amount of HCL and heat for 3 mins to hydrolyse the glycosidic bond
add sodium hydrogen carbonate powder to neutralise
then the last step same as the other
what test is used for proteins
the biuret test
what are the results of the biuret test
negative- remains blue
positive- changes from blue to purple
what is a negative control for the biuret test
to use water at the same volume as the sample
what would be a positive control for the biuret test
use albumein which is the white protein in egg whites
if a sample is solid what should you always do to make it easier to test
grind it up and add water
or melt if it is a lipid
what is the method of the biuret test
add buiret reagent in a 5:1 ratio to the sample, mix and leave
what is the method and the results for the translution mark test for lipids
put a drop of the sample onto some cloth and let it dry. if it is still transulcent after then it is a lipid. if it is opaque then it isnt
what is the method for the emulsion test
mix the sample with equal volumes of ethanol and water, shake vigourously
The first step is to add 2cm3 of the fish to a dry and grease-free test tube. Next, add 5cm3 of alcohol to the sample and shake the test tube. Finally, add 5cm3 water to the sample and shake the test tube.
what are the results for the emulsion test
negative- no emulsion will form
positive- a cloudy/milky white emulsion will form
what is a positive control for the emulsion test
use a known oil
what is a negative control for the emulsion test
use water
what is the method for the iodine test
use iodine dissolved in potassium iodide,
add and mix
what are the results for the iodine test
negative- stays yellow/brown
positive- turns from yellow/brown to blue/black
what is the iodine test for
starch
how can you test for water
water has a fixed melting and boiling point
testing for the presence of oil in the fish was observed under an optical microscope. There were many lipid droplets visible. Explain why.
The non-polar regions of lipids are hydrophobic and they form micelles when added to water. When the mixture is shaken, the micelles are broken into even smaller micelles and distributed through the water. The lipid droplets visible are the micelles distributed throughout the test tube.
