Chapter 3 Biological Tests Flashcards
What is the test for Sugars and positive result?
Benedict’s
Blue to Red
How does Benedict’s work?
Monosaccharides and some disaccharides are reducing sugars, reduce Cu 2+ ions in CuS04 to Cu +, blue to red
Add HCl non-reducing sugars to hydrolyse to monosaccharides
Green a mix of the Cu+ and Cu2+
What is the test for starch and positive result?
Add Iodine
Changes from yellow/orange to blue/black
How do you use a colorimeter when testing for sugars?
Make known concentrations of the sugar being tested, perhaps with serial dilutions
Use the colour opposite on the colour wheel to the starting solution colour, here as Benedict’s is blue, use red
Zero with water
Test the known concentrations for absorbance upon heating with Benedict’s and centrifuging to remove the filtrate. Plot a calibration curve
Hydrolyse (acid catalyst) your sample, neutralise, and add Benedict’s. Centrifuge your sample to remove the precipitate. Test the absorbance of the filtrate, compare to the calibration curve for concentration
If needed, control variables
What is the test for lipids and positive result?
Emulsion test
Add ethanol and shake, if turns cloudy, positive
How does the emulsion test work?
Lipids insoluble in water, but dissolves in alcohol
Ethanol soluble in water
Ethanol sinks, lipids form cloudy layer
What is the test for proteins?
Bieuret
Blue to purple
Forms complex with Amide bond, more bonds, darker colour
What type of disaccharide is sucrose?
A non reducing disaccharide
How do you test for sucrose?
Add HCl to hydrolyse sucrose into its constituent monomers Glucose and Fructose, heat
Add Carbonate to neutralise
Add Benedict’s and reheat, noting any colour changes
What are the steps for the extracting DNA practical? Why are these steps carried out?
Grind/crush the fruit to break down the cell walls.
Add detergent to break down cell membranes to release the cell contents into the solution
Add salt to break the hydrogen bonds between DNA and water molecules
Add an enzyme, protease, to break down the histones associated with the DNA
Add a layer of cold ethanol to form a precipitate with the DNA, which can be spooled out with a glass rod
How do you know which colour to use for colorimetry?
Use the colour opposite on the colour wheel for the starting solution
e.g Benedict’s originally blue, so use red
How did Stahl’s experiment prove that DNA replication was a semi conservative process?
DNA originally heavy Nitrogen 15, but then placed in light Nitrogen 14
Gen 0 contained the heavy isotope, they were the lowest in the tube as the density
Gen 1 had DNA only above Gen 0, as each DNA molecule had one heavy and one light strand
Gen 2 had DNA at the same height as before, 1 new and 1 old, but higher as well, which is DNA with only light Nitrogen
This process repeats generations, but the new DNA strands only contain Nitrogen 14, but the two strands of Nitrogen 15 still remain, there will always be two DNA molecules with 1 heavy, 1 light
How do biosensors detect glucose?
A protein or DNA is immobilised to the surface of the test strip
This will interact with glucose and cause the transducer to produce a current or release dye on the test strip
The results can then be analysed as a colour or digital signal
How do reagent strips work for testing glucose?
Place the sample of the test strip
If glucose is present, there will be a colour change
This can be compared to a colour chart to determine concentration
What does the Rf value tell you about the size of an amino acid?
Smaller Rf, less soluble in the mobile phase
So a larger molecule
