Carbohydrates (reducing + Non Reducing Sugars) Flashcards
(30 cards)
Describe the reducing sugars test
- Add Benedict’s reagent (blue) to your solution and place in a water bath (>80 Celsius)
- leave in water bath for approximately 5 minutes
- After the 5 minutes, if a brick-red precipitate is present then a reducing sugar is present
Why do you get a brick-red precipitate when test is positive
- The reducing sugars have the ability to reduce the Benedict’s reagent as they can donate an electron.
- The reducing monosaccharides donate electrons to the Cu2+ ions (which are blue). This causes them to be reduced (gain electron) to form Cu+ ion (which is a solid red precipitate)
Describe the test for a non reducing sugar (sucrose)
- Add acid (HCl) to the sample you took from the negative result and heat in a boiling water bath for approximately 2 minutes.
- Remove from water bath and add Alkali (sodium hydroxide) until fizzing/bubbling stops so you know the solution is neutralised.
-Add some Benedict’s reagent to the solution (turns blue) and place back into the water bath (>80 C) - After 5 minutes remove from water bath and a solid red precipitate represents a positive test.
Why did the non reducing sugar not give a positive result to the reducing sugars test?
- Non reducing sugars, such as sucrose, do not have the ability to donate an electron
- however in the non-reducing sugar test hydrolysis occurs and breaks the glycosidic bond between the two reducing monosaccharides (alpha glucose and fructose).
-These Monosaccharides have the ability to reduce the Cu2+ ion to form the Cu+ ion (solid red precipitate)
What monosaccharides make up lactose
-Galactose
-Alpha glucose
What monosaccharides make up maltose
- 2 Alpha glucose
What Monosaccharides make up sucrose
- Fructose
- Alpha glucose
What bond forms between two monosaccharides (sugars)?
Glycosidic bonds
Define a hydrolysis reaction
When you add water to a chemical reaction to help break the bonds (glycosidic) and form 2 smaller molecules.
Define a condensation reaction
When a chemical reaction releases water as a by- product of creating bonds.
What is an isomer?
Molecules that have the same chemical formula but a different arrangement of atoms
What are the 3 types of polysaccharides
- starch
- glycogen
- cellulose
Where is Starch found
- Found in plant cells in the form of granules
What is the function of starch?
Energy storage in plants
What monomers join to form starch?
- Alpha glucose
What are the 2 different structures of starch?
- coiled e.g amylose
- branched e.g amylopectin
Why are some starch molecules coiled?
- they form more 1- 4 glycosidic bonds
Why are some starch molecules branched?
- they form some 1 - 6 glycosidic bonds
How does starch’s structure make it better adapted for its function
- coiled, compact so good for storage
- branched, faster hydrolysis of the alpha glucose molecules for respiration
- Large + insoluble, doesn’t diffuse out of cells or affect water potential
Where is glycogen found?
Found in animal cells (muscles / liver)
What monomers form glycogen?
Alpha glucose
What’s the structure of glycogen?
It has a similar structure to amylopectin but it’s more branched due to the 1- 6 glycosidic bonds (coiled and branched)
What is glycogen’s main function?
- energy storage in animals
How does glycogen’s structure make it better adapted for its function?
Branched - faster hydrolysed of glucose molecules, helps for more efficient respiration
Coiled - compact so good for storage
Large insoluble - don’t diffuse out of cells / affect water potential
