Module 2 Section 2 - Biochemical Tests for Molecules Flashcards
What is the biochemical test for sugars
Benedict’s test
What 2 groups can sugars be classified as
Reducing or non reducing
The Benedict’s test differs….
Depending on the type of sugars you’re testing for
What do reducing sugars include
All monosaccharides and some disaccharides
What do you add to a sample of reducing sugars to test for it
Benedict’s reagent
What other step do you do to the sample after adding the Benedict’s reagent
Heat it in a water bath that has been brought to the boil
How does the colour of the precipitate change
Blue - Green - yellow - orange - brick red
What happens if the test is positive
A coloured precipitate will form
Why do I always add excess Benedict’s solution
To make sure all the sugar reacts
What can you conclude about the test
The higher the concentration of reducing sugars the further the colour change goes
What happens if the test of the reducing sugars is negative
There still could be non reducing sugars present
What is the first step of breaking down non reducing sugars
You have to break them down to monosaccharides
How do you break down the sugar to a monosaccharide to test for non reducing sugars
Get a new sample of the test solution, add dilute hydrochloric acid and carefully heating it in a water bath that has been brought to a boil
After diluting hydrochloric acid and heating it what do you do to the sample to test for non reducing sugars
You neutralise it with sodium hydrogencarbonate and then carry the test out as you would for reducing sugars
What happens if the test is positive
It will form a coloured precipitate
What happens if the test is negative
The solution will stay blue meaning it doesn’t contain any sugars
What is glucose best tested using
Test strips coated in reagent
What happens if glucose is present
A colour change
What can the colour change be compared to
A chart which gives the indication of concentration of glucose present
What are the strips useful for
Testing a person’s urine for glucose - indicates they may have diabetes
What test is used for starch
Iodine test
What do you add to the test sample
Iodine which is dissolved in potassium iodide solution
What happens if starch is present
The sample changes colour from brown/orange to a dark blue/black colour
What happens if no starch is detected
It stays brown/orange colour
What test is used for proteins
Biuret test
What does the test solution for testing protein need to be
Alkaline
How do you make the test solution alkaline
Add a few drops of sodium hydroxide solution
After adding sodium hydroxide solution what do you add
Copper (II) sulfate solution
What happens if protein is present
The solution turns purple
What happens if there no protein present
The solution stays blue
what test is used for lipids
the emulsion test
what is the first stage of the emulsion test
shaking the test substance with ethanol for about a minute
what do you do after shaking the test substance and ethanol
pour the solution into the water
what happens if a lipid is present
the solution will turn milky
what conclusion can be made about this test
the more lipid there is the more noticeable the milky colour will be
what happens if the there are no lipids present
the solution will stay clear
what is used to determine the concentration of a glucose solution
colourimeter
how do you get a quantitative estimate for how much glucose is in a solutions
you can use benedicts reagent and a colourimeter
what is a colourimeter
a device that measures the strength of a coloured solution by seeing how much light passes through t
what does a colourimeter measure
absorbance
the more the colour of the solution is……
the higher the absorbance is
when is it easiest to measure the concentration of glucose
after the test is finished. meaning the higher the glucose concentration the lower absorbance of the solution
