3.1.2 Carbohydrates Flashcards
(21 cards)
What is a monosaccharide
- monomers which are joined to make larger carbohydrates
Examples of common monosaccharides
Glucose, galactose and fructose (all C6 sugars)
What reaction forms monosaccharides, describe this reaction
- condensation
- new covalent bond formed = glycosidic bond
- loss of water
How is a disaccharide formed
- condensation of 2 monosaccharides
What monosaccharides from maltose
2 alpha glucose
What monosaccharides form sucrose
glucose and fructose
What monosaccharides form lactose
- glucose and galactose
Describe the structure of starch
- alpha glucose
- linear chain
- alpha 1-4 glycosidic bonds
- coiled / helical
- both branched and unbranched (Amylose = unbranched, amylopectin = branched)
Describe the structure of glycogen
- alpha glucose
- branched
- alpha -1-4- glycosidic bonds AND alpha -1-6- glycosidic bonds
Describe the structure of cellulose
- beta glucose
- linear chain
- beta -1-4- glycosidic bonds
- alternate glucose molecules inverted
- H2 bonds form between adjacent chains, forming micro fibrils
Benefits for glycogen/amylose - Polymer of alpha glucose
provide respiratory substrate (molecule that can be oxidised in respiration to release energy)
Benefits for amylose- helical
compact (more can be stored in the cell)
Benefits for glycogen- Spherical
compact (more can Stored in the cell)
Benefits for glycogen- Branched
can be hydrolysed more rapidly
Benefits of glycogen/amylose- Insoluble
does not affect movement of water into cell by osmosis
Cant diffuse out of the cell
amylose/glycogen- Large molecule so…
cannot diffuse out of the cell
Cellulose- H2 bonds between adjacent chains so…
From microfibrils = provides high tensile strength (cell wall is strong) - flexible cell walls
Cellulose- Straight chains so…
close packing, forming stronger fibres
Test for starch
- add iodine
- turns from orange to blue/black
Reducing sugar test (e.g. glucose, maltose)
- add Benedict’s solution
- heat at 85 degrees C in water bath
- turns from blue to brick red (low conc = green/yellow/orange)
Reducing sugar = Donating electrons to another chemical (copper 2 to copper 1)
Non-reducing sugar test (e.g. sucrose)
Initial Test with Benedict’s Solution: First, you test the sugar solution with Benedict’s solution. If there’s no colour change (stays blue), it indicates the absence of reducing sugars.
Hydrolysis Step: Heat the sugar solution with hydrochloric acid to hydrolyse any non-reducing sugars into their monosaccharide components.
Neutralisation: After hydrolysis, neutralise the solution with sodium bicarbonate.
Re-test with Benedict’s Solution: Add Benedict’s solution and heat again. A brick-red precipitate indicates the presence of reducing sugars formed from the hydrolysis of non-reducing sugars.
