Biochemical Tests Flashcards
What is the test for starch?
1)Add iodine
2)If starch is present - positive result is blue/black.
What are the 5 biochemical tests we need to know?
Reducing sugars
Non reducing sugars
Proteins
Lipids
Starch
What colour is iodine?
Orange
What is the test for reducing sugars?
1)Add Benedict’s Reagent and heat.
2)A positive test - solution turns from blue –> green,yellow,orange or brick red.
For the sugars test, what does a more red colour mean?
The higher the concentration of reducing sugar.
For sugars, why does the colour change occur at the top of the solution first?
The hotter particles of the solution are rising and thus the hottest point of the solution will be at the top. Thus, molecules will have the most kinetic energy at the top meaning more successful collisions and the reaction will be happening faster.
What is the non reducing sugar test?
1)Do Benedict’s test first.
2)Add acid and boil for atleast 2 minutes.
3)Cool the solution and add an alkali.
4)Add Benedict’s reagent and heat again.
5)A positive test = solution turns from blue –> green, yellow, orange, or brick red.
Why do we do Benedict’s test first in the non reducing sugars test?
To confirm is isn’t a non reducing sugar.
Why do we add acid and boil for atleast 2 minutes in the non reducing sugar test?
To hydrolyse the glycosidic bonds so the glucose can be broken down into glucose and fructose which are reducing sugars - acid hydrolysis.
Why do we cool the solution for non reducing sugars test?
For safety reasons.
Why do we add an alkali in the non reducing sugars test?
To neutralise the solution.
5 examples of reducing sugars?
Glucose
Fructose
Galactose
Lactose
Maltose
Example of non reducing sugar?
Sucrose
What are reducing sugars?
Reducing sugars can reduce the copper sulphate in Benedict’s reagent to copper oxide.
What are non reducing sugars?
The reducing group is involved in the glycosidic bond and thus sucrose cannot reduce copper sulphate to copper oxide. When sucrose is hydrolysed the glycosidic bond is broken and thus the reducing group becomes exposed.
