carbohydrates

Question 1

Complete the following table to show three other differences in the structures of starch (amylose) and cellulose molecules.

Answer 1

(contains) α / alpha / A /
a ,-glucose
(contains) β / beta / B / b
, -glucose ;
α / alpha / A / a 1-4
glycosidic bonds
β / beta / B / b 1-4
glycosidic bonds ;
all , monomers / AW , in
same orientation
alternate monomers at ,
180° / AW , to each other ;
granular / not fibrous fibrous / not granular ;
H bonds within molecule
/ no (H) bonds (between
molecules)
(H) bonds between
adjacent molecules

Question 2

benedict’s test for reducing sugars

Answer 2

1) reducing sugars = all monosaccharides(glucose) and some dissacharides(maltose+lactose)
2) add excess blue benedict’s reagent to a sample and heat in water bath that’s been brought to boil
blue–>green–>yellow–>orange–>brick red

the higher the conc of reducing sugar, the further the colour change + filter solution and weigh precipitate

Question 3

benedict’s test for non-reducing sugars

Answer 3

non reducing sugars must be broken down into monosaccharides

1) add dilute hcl and careful heating in water bath that been brought to a boil
2) neutralise with sodium hydrogencarbonate

Question 4

glucose test

Answer 4

1) test strips coated in reagent
2) colour change comparison to a chart confirms glucose presence
useful for diabetes urine tests

Question 5

starch test

Answer 5

1) add iodine dissolved in potassium iodide solution to sample
+ browny orange to blue black
- browny orange

Question 6

colorimetry

Answer 6

colorimeter measures strength of coloured solution via the amount of light that passes through it
aids a quantitative estimate of glucose conc via benedicts test
1) benedict’s test(same amount) + negative control(pure water)
2) remove any precipitate - leave for 2hr/centrifuge
3) use colorimeter with red filter to measure absorbance of remaining benedicts solution in each tube
4) plot calibration curve using results of absorbance against glucose conc

Question 7

serial dilution

Answer 7

1) line up 5 test tubes in a rack
2) add 10cm3 of initial 40mM glucose conc to first 5 test tubes an 5 cm3 to ither 4
3) using a pipette draw 5cm3 from first test tube and transfer to next tube
4) repeat process

Question 8

Examples (3) of monosaccharides

Answer 8

Glucose- reactant in respiration, product of broken down carbohydrates

Fructose- found in fruits + nectar, very soluble,

Galactose- not very soluble, forms glycolipids and glycoproteins

Question 9

What are the four main macromolecules?

Answer 9

• Glycogen
• Chitin
• Cellulose
• Starch

Question 10

Give examples (2) of pentose sugars;

Answer 10

• Ribose

- Deoxyribose

Question 11

What are disaccharides and give examples;

Answer 11

• two simple monosaccharides chemically joined
• maltose
• sucrose
• lactose

Question 12

Describe maltose

Answer 12

• two glucose monosaccharides

- alpha 1-4 glycosidic bond

Question 13

Describe sucrose

Answer 13

• glucose and fructose chemically joined

- alpha 1-4 glycosidic bond

Question 14

Describe lactose;

Answer 14

• galactose and glucose bond

- beta 1-4 glycosidic bond

Question 15

What does ‘amphipathic’ mean?

Answer 15

Having one hydrophilic and one hydrophobic end