Monomers, Polymers, Carbohydrates

Define monomer. Give some examples.

smaller units that join together to form larger molecules - monosaccharides (glucose, fructose, galactose), amino acids, nucleotides

define polymer. give some examples

molecules formed when many monomers join together - polysaccharides, proteins, DNA/RNA

what happens in a condensation reaction

a chemical bond forms between two molecules and a molecule of water is produced

what happens in a hydrolysis reaction

a water molecule is used to break a chemical bond between two molecules

name the 3 hexose monosaccharides

glucose, fructose, galactose - all have the molecular formula C6H12O6

name the type of bond formed when monosaccharides react

(1,4 or 1,6) glycosidic bond - 2 monomers = 1 chemical bond = disaccharide- multiple monomers = many chemical bonds = polysaccharide

name 3 disaccharides. describe how they form

condensation reaction forms glycosidic bond between 2 monosaccharides
maltose: glucose + glucose
sucrose: glucose + fructose
lactose: glucose + galactose
all have molecular formula C12H22O11

describe the structure and functions of starch

storage polymer of a-glucose in plant cells
- insoluble - no osmotic effect on cells
- large - does not diffuse out of cells
made from amylose = 1,4 glycosidic bonds, helix with intermolecular H-bonds = compact
and amylopectin = 1,4 and 1,6 glycosidic bonds, branced = many terminal ends for hydrolysis into glucose

describe the structure and function of glycogen

main storage polymer of a-glucose in animal cells, but also found in plant cells
- 1,4 and 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis
- insoluble = no osmotic effect and does not diffuse out of cells
- compact

describe the structure and functions of cellulose

polymer of B-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)
- 1,4 glycosidic bonds
- straight-chain, unbranched molecules
- alternate glucose molecules are rotated 180 degrees
- H-bond crosslines between parallel strands form microfibrils = high tensile strength

describe the Benedict’s test for reducing sugars

1. add an equal volume of Benedict’s reagent to a sample

2. heat the mixture in an electric water bath at 100 C for 5 mins

3. positive result: colour change from blue to orange/brick red precipitate forms

Describe the Benedict’s test for non-reducing sugars

1. negative result: Benedict’s reagent remains blue

2. hydrolose non-reducing sugars e.g. sucrose into their monomers by adding 1cm cubed of Hal. Heat in a boiling water bath for 5 mins

3. neutralise the mixture using sodium carbonate solution

4. proceed with the Benedict’s test as usual

describe the test for starch

1. add iodine solution

2. positive result: colour change from orange to blue-black

outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

1. make standard solutions with known concentrations. Record absorbance or % transmission values

2. plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis)

3. record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration