1.2 Flashcards
What is a disaccharide?
When two monosaccharides join together to form a disaccharide
What is a polysaccharide?
When several monosaccharides join together to form a polysaccharide
3 disaccharides and what are they made of?
• Maltose (C12H22O11) is made from two alpha-glucose molecules
• Lactose (C12H22O11) is made from glucose and galactose
• Sucrose (C12H22O11) is made from glucose and fructose
3 types of polysaccharides and their functions?
• Cellulose – provides structural support in plants, made from β-glucose molecules
• Starch – storage molecule in plants, made from α-glucose
• Glycogen - storage molecule in animals, made from α-glucose
Which reaction causes the formation of disaccharides and polysaccharides?
Monosaccharides can be joined together to form disaccharides and polysaccharides via a condensation reaction
What type of bond is formed in a condensation reactions and what is released as a product?and what is it controlled by?
An oxygen bridge, called a glycosidic bond, is formed between the two monomers. Water is released as a product. The reaction is controlled by enzymes.
What is the opposite of a condensation reaction?
The opposite to condensation is hydrolysis, when water is added to break the glycosidic bond.
Testing for starch?
1)Add a few drops of yellow-brown iodine solution to a sample.
2)The iodine solution will turn blue-black is iodine is present.
3)It will remain a yellow-brown colour is starch is not present
Testing for a non-reducing sugar?
1)If the sample is not already in liquid form you must grind it up in water
2)Add another 2cm^3of the food sample being tested to 2 cm^3of dilute hydrochloric acid in a test tube
3)place the test tube in a gently boiling water bath for 5 minutes.
4)The dilute hydrochloric acid will hydrolyse any disaccharide present into its constituent monosaccharides.
5)Slowly add some sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid. (Benedict’s reagent will not work in acidic conditions.)
6)Test with pH paper to check that the solution is alkaline.
7)Retest the resulting solution by heating it with 2 cm^3of Benedict’s reagent in a gently boiling water bath for 5 minutes.
8)If a non-reducing sugar was present in the original sample, the Benedict’s reagent will now turn orange-brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.
