Biology topic =disaccharides and poylsaccharides(1.3)

What are pairs of monosaccharides called?

disaccharides

What are many monosaccharides called?

polysaccharides

Glucose+glucose

maltose joined by an aplha1-4 glycosidic bond

\
(enzyme that breaks it up= maltase)

Glucose+fructose

Sucrose joining by an Alpha 1-4 glucosidic bond

\
(enzyme that breaks it up= sucrase)

glucose+galactose

lactose joined by a beta 1-4 glycosidic bond

(enzyme that breaks it up= lactase)

what happens when these monosaccharides join?

a molecule of water is removed and the reaction is called a =condensation reaction
=bond is called glycosidic bond

what happens when water is added to a disaccharide?under suitable conditions

it breaks the glycosidic bond releasing the constituent monosaccharides.=called hydrolysis

Testing for non-reducing sugars

We can't use Benedict test because they do not change colour when heated.

in order to detect it must be hydrolysed into its monosaccharide components by hydrolysis.components

method:

1)if sample is not ready in liquid from, it must be first be ground up in water.

2)add 2cm cubed of the food sample being tested to 2cm cubed of Benedict regent in a test tube and filter.

3)place the test tube in gently boiling water for 5 minutes.if the Benedict regent does not change colour(remains blue=no reducing sugar present).

4) add another 2cm cubed of the food sample to 2cm cubed of dilute hydrochloric acid in a test tube and place the test tube in a gently boiling water bath for 5 min. The dilute hydrochloric acid will hydrolyse any disaccharide present into its constituent monosaccharide.

5)slowly add some sodium hydrogen carbonate solution to the test tube in order to neutralize the hydrochloric acid. Test with pH paper to check solution is alkaline.

6) re test the resulting solution bye hating 2cm cubed of ben reagent in gently boiling water for 5m.

7)=if a non-reducing sugar was present in the original sample, the Benedict regent will now then orange/brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.

What are polysaccharides?

-formed :combining many monosaccharides together.
Bonds:the monosaccharides are joined by glcosic bonds that were formed by condensation reactions.
-very large
-they are insoluble=makes them suitable for storage
-and as structural components of cells.

what happens when polysaccharide are hydrolysed?

break down into disaccharides or monosaccharides.

Examples of polysaccharide

Cellulose =not used for storage but give structural support to plant cells.
-starch
-glycogen

test for starch?

-place 2cm cubed of the sample being tested into a test
-add 2 drops of iodine solution and shake/stir
-the presence of starch is indicated by a blue-black colouration.