biological molecules

Question 1

3 common disaccarides

Answer 1

maltose- from 2 glucose molecules
sucrose- fructose and glucose
lactose- glucose and galactose

Question 2

test for reducing sugars

Answer 2

-these include monosaccharides and some disaccharides. eg maltose and lactose
- a reducing sugar is one that can reduce (donate electrons) to another chemical. In this case the chemical is Benedict’s reagent
-benedicts is an alkaline solution of copper (11) sulfate.
- heat solution in hot water bath for 5 mins with benedicts.
If positive should form green to yellow to orange to brick red precipitate. Higher the concentration the further along the colour change

Question 3

test for non reducing sugars

Answer 3

carbohydrates and some disaccharides eg sucrose are non reducing sugars.
- add benedicts and heat
- if no colour change then reducing sugar is NOT present
- then add HCl and heat again. The HCl will hydrolyse any disaccharide present
- then add sodium hydrogencarbonate solution the neutralise the HCl. Test with pH paper to ensure solution is alkaline
- then retest by adding Benedict’s and heating again
- if non reducing sugar then colour change will be same as benedict’s test for reducing sugar

Question 4

starch test

Answer 4

add iodine
if starch is present solution will turn blue-black

Question 5

test for proteins

Answer 5

-biuret test
- add sodium hydroxide and copper (11) sulfate to form biuret solution
- solutions turns from blue to lilac/ purple