Biochemical Tests Flashcards
What is a reagent?
A compound/mixture added to a system to start or test a chemical reaction
What is the test for starch?
- Place sample of starch into test tube
- Then add two drops of iodine solution
- Stir
- If starch is present, a colour change from orange to blue/black should occur
What is the reagent in the test for starch?
Iodine
What temperature should the test for starch be?
Room temperature
What will happen if proteins are absent from the sample?
If there are no proteins, the colour will remain blue
What is the reagent for the test for proteins?
Biuret
What is the test for proteins?
- Add sample of protein to test tube
- Add biuret to protein sample and mix
- If protein is present, a colour change from blue to purple will occur
What is the reagent for the test for lipids?
Ethanol
What is the test for lipids?
- Add lipid sample and ethanol to test ube
- Shake the tube thoroughly to dissolve and lipid in the sample
- Add water and shake gently again
- If lipids are present, a white milky emulsion will form
Why is there a cloudy appearance in the test?
A cloudy appearance occurs because the light shown through this emulsion is refracted as it passees from oil droplets to water droplets
What is a reduction reaction?
A chemical reaction involving the gain of electrons or hydrogens
Why is there a cloudy appearance?
The cloudy appearance is due to the lipid in the sample being finely dispersed in the water to form an emulsion
What is a reducing sugar?
A sugar that can donate electrons to (or reduce) another chemical
What show a higher concentration of reducing sugar in a test for reducing sugars?
If the solution is more red, like the colour of red is deep or darker, there is a higher concentration of reducing sugars
What happens when a reducing sugar is heated with Benedict’s reagent?
When a reducing sugar is heated with Benedict’s reagent it forms an insoluble red precipate of copper oxide
What is the test for reducing sugars?
- Grind up sample being tested, if not already liquid
- Add sample of reducing sugar to test tube
- Add equal volume of Benedict’s reagent
- Heat the mixture to a gentle boil
- A positive test should show a soluti
What are non - reducing sugars?
A sugar that serves as a reducing agent due to its free aldehyde or ketone functional groups in its molecular structure
What is an example of non - reducing sugars?
Sucrose
What is another reason non - reducing sugars are non - reducing? (colour)
This is because they do not change the colour of Benedict’s reagent when heated
How do you detect a non - reducing sugar?
To detect a non - reducing sugar, it must be hydrolysed into its monosaccharide components
What is the test for non - reducing sugars?
- Grind up the sugar sample if not already liquid
- Add liquidated sample and Benedict’s reagent to a test tube
- Conduct Benedict’s test, once you receive a negative result, add dilute hydrochloric acid
- Heat test tube and bring to a gentle boil
- Allow solution to cool, then add sodium hydrogen carbonate sodium to neutralise the solution
- Retest the solution by adding Benedict’s reagent and heat the solution
- A positive test should show show a colour change from blue to brick red
