1.2 CARBOHYDRATES

Question 1

Name

3 hexose monosaccharides

Answer 1

• glucose
• fructose
• galactose

all have the molecular formula C₆H₁₂O₆

Question 2

Name

type of bond between monosaccharides

Answer 2

(1,4 or 1,6) glycosidic bond

Question 3

Name and describe

3 disaccharides and how they form

Answer 3

• maltose: glucose + glucose
• sucrose: glucose + fructose
• lactose: glucose + galactose
  condensation reaction forms glycosidic bond between 2 monosaccharides

Question 4

Describe

α-glucose stucture

Answer 4

3 -OH branches on the bottom

Question 5

Desribe

β-glucose

Answer 5

2 -OH branches on the bottom

Question 6

Describe

starch functions and features

not components

Answer 6

storage polymer of α-glucose in plant cells
* insoluble = no osmotic effect on cells
* large = doesn’t diffuse out of cells

Question 7

Describe

starch structure

Answer 7

amylose:
* 1,4 glycosidic bonds
* helix w/ intermolecular H-bonds = compact

amylopectin:
* 1,4 & 1,6 glycosidic bonds
* branched = many terminal ends for hydrolysis into glucose

Question 8

Describe

cellulose structure and functions

Answer 8

polymer of β-glucose gives rigidity to plant cell walls
* prevents lysis under turgor pressure
* holds stem up

• 1,4 glycosidic bonds
• straight-chain, unbranched molecule
• alternate glucose molecules are rotated 180°
• H-bond crosslinks between parallel strands form microfibrils = high tensile strength

Question 8

Describe

glycogen structure and functions

Answer 8

main storage polymer of α-glucose in animal cells
* 1,4 & 1,6 glycosidic bonds
* branched = many terminal ends for hydrolysis
* insoluble = no osmotic efffect & doesn’t diffuse out of cells
* compact

also found in plant cells

Question 9

Describe

Benedict’s test for reducing sugars

Answer 9

1. Add an equal volume of Benedict’s reagent to a sample
2. Heat the micture in an electric water bath at 100°C for 5 mins
3. +ive result: colour change from blue to orange & brick-red precipitate forms

Question 10

Describe

Benedict’s test for non-reducing sugars

Answer 10

1. -ive result: Benedict’s reagent remains blue
2. hydrolyse non-reducing sugars with 1cm³ and heat in boiling water bath for 5 mins
3. neutralise micture w/ sodium carbonate solution
4. proceed w/ Benedict’s test

Question 11

Describe

test for starch

Answer 11

1. add iodine solution
2. +ive: colour change from orange to blue-black

Question 12

Outline

use of colorimetry for qualitative results of sugar and starch presence

Answer 12

1. make standard solutions w/ known conc.
   record absorbance values
2. Plot calibration curve: absorbance (y-axis). conc. (x-axis)
3. record absorbance values of unknown samples
4. use calibration curve to read off conc.