1.3 - Carbohydrates - disaccharides and polysaccharides Flashcards
What is a disaccharide?
Two monosaccharides joined via glycosidic bond,
Which disaccharide do two glucose monomers form?
Glucose + Glucose = Maltose
Which disaccharide does fructose and glucose form?
Fructose + Glucose = Sucrose
Which disaccharide does galactose and glucose form?
Galactose + Glucose = Lactose
What is the bond that is formed when two monosaccharides join?
Glycosidic Bond
What reaction joins two monosaccharides?
Condensation Reaction.
What reaction splits two monosaccharides?
Hydrolysis Reaction
What are non-reducing sugars?
Non reducing sugars do not change the colour of Benedict’s reagent when they are heated with it.
Give an example of a non-reducing sugar.
Sucrose.
How do you test for a non reducing sugar?
- If Benedict’s reagent does not change colour, then a reducing sugar is not present.
- Add another 2cm³ of food sample to 2cm³ of dilute HCL in a test tube and gently boil for 5 mins. The HCL will hydrolyse any disaccharides present.
- Slowly add sodium hydrogencarbonate solution in order to neutralise the acid. Test with PH paper.
- Re test with benedict’s solution, if a non reducing sugar was present there will now be a colour change.
What is a polysacchride?
Polymers made by joining many monosaccharide molecules.
Give features of polysaccharides.
- Large
2. Insoluble
Give uses of polysaccharides
- Good for storage (large and insoluble)
2. Structural support
Give an example of a polysaccharide.
Starch found in plants in form of starch grains. Made of many ⍺-glucose molecules.
What is the test for Starch?
Starch is easily identified by its ability to change the colour of iodine from yellow to blue/black.
