Slides - Unit 18

In the Water: Plastic bags
clog up drains
and river beds,
and can cause

flooding.

Plastic items The When fish, birds
collect in middle problem and other animals

of oceans, with swallow plastic,
carried by plastics they cannot digest
current.
it. It fills their
stomachs, and they

die of hunger.

Fish, birds and
other animals get

tangled in
plastic waste. It
can choke them.

Tackling the Pollution:

1. Many countries have now banned plastic bags and
in some countries, shops charge customers for the
use of plastic bags.

2. In some countries, plastic materials are collected for
recycling.

3. Chemists are trying to develop biodegradable
plastics, that will break down in the natural
environment.

4. Semi-degradable plastics already exist. These
break down into small fragments over time, when
exposed to heat and moisture, or bacteria.

18.6
Natural Polymers in
Food (Part I)

Learning objectives:
■ Name two natural polymers in food, and state what

monomers they are built from
■ Draw simple diagram to show how starch formed by

condensation polymerisation

Two Natural Polymers in Food:

1. Food contains two natural polymers:
carbohydrates and proteins.

2. Plants make glucose, a sugar from carbon
dioxide and water, by photosynthesis.

3. Plants use the synthesised glucose
molecules as monomers, to make long chain
starch and cellulose.

4. Starch and cellulose are carbohydrates.

5. Plants also use glucose, plus nitrates and
other compounds from the soil, to make
amino acids.

6. Then, plants use amino acid molecules as
monomers, to make proteins.

Glucose:

1. Glucoses are monosaccharide which
contains single sugar unit.

2. These units join to form a polymer called
polysaccharide or complex carbohydrate
(e.g. starch).

From Glucose to Carbohydrate:

+++

From Glucose to Carbohydrate:

1. Glucose has five -OH groups, but only 2 of
them take part in polymerisation.

2. We draw the sugar units simply, like this, with
just two OH groups shown:

HO OH

3. How the glucose molecules join together?

i. By condensation polymerisation, with the elimination of water
molecules.

ii. H from the -OH group on one molecule combines with an -OH
group from another molecule, to form a water molecule.

glucose monomer glucose monomer

HO OH HO OH

H-OH

(water)

3. How the glucose molecules join together?

ii. A new C-O link form between the molecules.

HO OH HO OH

OO + H2O

water
molecules
eliminated

18.7
Natural Polymers in
Food (Part II)

Learning objectives:
■ Draw simple diagram to show how protein formed by condensation

polymerisation

■ Explain what hydrolysis is
■ Describe how the hydrolysis of carbohydrates and proteins can be

carried out in the lab, and name the products of complete hydrolysis

■ Describe how to carry out paper chromatography to identify products

of hydrolysis

Protein:

1. Proteins are natural polymers which contain the
amide linkage (as Nylon does).

2. Like synthetic polymers, they are built up by small
units joining together.

3. All living things contain proteins.

4. Proteins are an important constituent of food.

Amino acids:

1. Living organisms use amino acid molecules as
monomers, to make proteins.

2. Amino acids are carboxylic acids, with an amino
group (NH2) on the carbon atom next to the COOH
group.

R stands for the rest of the molecule. For example:
- in glycine, R is H
- in alanine, R is CH3

glycine alanine



3. How the amino acid molecules join together?

i. By condensation polymerisation, with the elimination of water
molecules.

amino acid 1 amino acid 2

ii. H from the -NH2 group on one molecule combines with an OH from
the -COOH group of another molecule, to form a water molecule.

3. How the amino acid molecules join together?

iii. A new C-N link form between the molecules.

iv. In protein, the amino acids are joined by amide linkage like those in
nylon.

H OH + H2O

amide linkage

Hydrolysis of Proteins and Carbohydrates:

1. Proteins can be broken down into amino acids by a
process known as hydrolysis.

2. Hydrolysis is breaking down a compound using
water.

3. Hydrolysis is the reverse reaction to the formation
of protein.

4. Water splits the amide linkages apart again to form
the original amino acids.

5. Acid is used as a catalyst.

6M HCl (catalyst)

6. The amino acids in a protein can be analysed by
hydrolysing the protein then using chromatography
to separate the amino acids present.

7. Amino acids are colourless, so they are made visible
on the chromatography paper using a locating
agent.

8. Each amino acid has a different Rf value, which
allows it to be identified.



9. As with proteins, starch and other complex
carbohydrates can be hydrolysed to give simple
sugars (e.g glucose).

10. Water molecules split the links between the sugar
units.

11. Enzymes or acids catalyse this process.

12. The products of this hydrolysis can be separated and
analysed using chromatography, in a similar way to
that used to separate amino acids from the
hydrolysis of proteins.

Exercise 1:

Polymer is a large molecule, which made from many
monomers joined together.

amide linkage
Refer to an object that can be broken down by microbes
or bacteria.

starch / cellulose / polysaccharides

n

Exercise 1:

Polymer is a large molecule, which made from many
monomers joined together.

hydrolysis
acidic condition

distance moved by substance
distance moved by solvent