1.3: Carbohydrates- disaccharides and poly

Question 1

What are the names of

Glucose + glucose

or glucose + fructose

or glucose+ galactose

Answer 1

Two monosaccharides in a pair form a disaccharide

Maltose

sucrose

lactose

Question 2

What is the bond between two monosaccharides?

How is it formed

Answer 2

Glycosidic bond

Formed in a condensation reaction so a molecule of water is removed

Question 3

What happens when water is added to a disaccharide

Answer 3

Hydrolysis: it breaks the glycosidic bond holding the monosaccharides together

Question 4

How do 2 alpha glucose bond together

Answer 4

Glycosidic bond

The OH of one, with the H from the OH of another

OH—-H (O)

Question 5

What element acts as the glycosidic bond holding two monosaccharides together

How do u draw it

Answer 5

Oxygen is left over from the OH where only the H bonded but not the oxygen

|——o—–|

|

Question 6

How do you know if a sugar is non reducing

Answer 6

.They don’t change colour with Benedict’s solution when heated with it.

Question 7

How to know if there is a non reducing sugar

Answer 7

. Make it liquid form eg ground up with water
. Add equal amounts of food sample to benedict’s reagent in a test tube and filter
. Place in boiling water bath for 5 minutes, if it doesn’t change colour it’s non reducing.

Question 8

Test for a non reducing sugar

Answer 8

. Add 2cm of food sample with 2cm dilute HCL in a test tube and put in boiling water for 5 mins
. The HCL will hydrolyse any disaccharide present into its monosaccharides

. Slowly add sodium hydrogen carbonate solution to test tube to neutralise HCL
(as Benedict’s reagent doesn’t work in acidic conditions).
Test with PH paper to make sure its alkaline

. Then retest by heating it with Benedict’s solution in boiling water bath

. If non reducing sugar is present, it turns orange/brown due to reducing sugars produced from hydrolysis of non reducing sugar

Question 9

What are polysaccharides

Answer 9

Polymers, formed by combining together many monosaccharide molecules

The monosaccharide molecules are joined together by glycosidic bonds that were formed in condensation reactions.

Question 10

Why are polysaccharides good storage molecules

Answer 10

. They’re insoluble due to them being very large molecules.
. This makes them suitable for storage

Question 11

What happens when polysaccharides are hydrolysed

Answer 11

. They break down into disaccharides and monosaccharides

C6-C6-C6-C6-C6-C6 poly

C6-C6 C6-C6 C6-C6 di

C6 C6 C6 C6 C6 C6 mono

Question 12

How do you test for starch

Answer 12

. Place 2cm of sample into test tube, or add 2 drops into a depression of spotting tile

. Add 2 drops of iodine solution, and shake or stir

. Presence of starch is labelled by a blue black colouration, turning from a yellow colour previously

Carry out at room temp