This is a PowerPoint presentation for Topic 1 in the Edexcel Biology B A Level course that starts in 2015. This is a free sample, the full PowerPoint presentation is available to purchase here: https://sellfy.com/MrExham

1. A Level Biology
MAKING SENSE OF
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Copyright©2017HenryExham
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Copyright©2017HenryExham

2. Copyright © 2015 Henry Exham
• The basic unit of life is a cell.
• To really understand how it works you need to
know what it is made from.
• In this topic you will learn about the most
important molecules that are used to make
cells and other important structures in
biology.
• This is the chemistry of life!
2
Biological Molecules
Introduction

3. Biological Molecules
MAKING SENSE OF
1.1 Carbohydrates
1.2 Lipids
1.3 Proteins
1.4 DNA and Protein Synthesis
1.5 Enzymes
1.6 Inorganic Ions
1.7 Water
3

4. Copyright © 2015 Henry Exham
• Do you know the difference between
monosaccharides, disaccharides and polysaccharides?
• What is the structure of alpha and beta glucose?
• What is the structure of ribose?
• Can you explain how condensation reactions are used
to form glycosidic bonds between sugar molecules, and
hydrolysis reactions break these bonds?
• Can you state the structures and bonding of the
following molecules: sucrose, lactose, maltose, starch
and glycogen.
• How does the structure of glucose, starch, glycogen
and cellulose relate to their function?
4
1.1 Carbohydrates
Objective Questions

5. Copyright © 2015 Henry Exham
• Cells use carbohydrates as a source of energy
and a way of storing energy.
• The source of energy is usually small simple
sugars such as glucose.
• Plants can store this in the form of starch,
whilst animals store it as glycogen.
• Carbohydrates are made of three elements:
carbon, hydrogen and oxygen.
• We can organise carbohydrates into different
groups based on their size.
5
1.1 Carbohydrates
Introduction

6. Copyright © 2015 Henry Exham
Monosaccharides (one
sugar)
6
1.1 Carbohydrates
Mono, di and poly saccharides
Disaccharides (two sugars)
Polysaccharides (many sugars)
Hexose Pentose
Oligosaccharides (3-10 sugar units) Polysaccharides (more than 10)

7. Copyright © 2015 Henry Exham
• Monosaccharides are simple sugars.
• You should be familiar with the following
examples:
– Pentose Sugars (Ribose and Deoxyribose) these
have 5 carbon atoms.
– Hexose Sugars (Glucose, fructose and galactose)
these have 6 carbon atoms.
7
1.1 Carbohydrates
Monosaccharides
You must be able to describe the structure of ribose and glucose in more detail.

8. Copyright © 2015 Henry Exham
• This is the structure of the pentose sugar
ribose
8
1.1 Carbohydrates
Monosaccharides
O
CC
C C
OH
OHOH
H
HH
H
CH2OH
RIBOSE

9. Copyright © 2015 Henry Exham
• Glucose actually exists in two forms (isomers)
and you need to know both of them.
9
1.1 Carbohydrates
Monosaccharides
α-GLUCOSE β-GLUCOSE
C C
C O
CC
CH2OH
OH
H
H
H
H
H
OH
HO
OH 1
23
4
5
6
C C
C O
CC
CH2OH
H
H
H
H
H
OH
OH
HO
OH 1
23
4
5
6
• The carbon atoms are numbered to help identify the molecule.

10. Copyright © 2015 Henry Exham
• The difference is small, just the hydrogen and hydroxide
swapped over on the 1st Carbon.
• However this has a big impact when glucose forms
polymers as we will see in the polysaccharides section.
10
1.1 Carbohydrates
Monosaccharides
α-GLUCOSE β-GLUCOSE
1
23
4
5
6
1
23
4
5
6
C C
C O
CC
CH2OH
H
H
H
H
H
OH
OH
HO
OH
C C
C O
CC
CH2OH
OH
H
H
H
H
H
OH
HO
OH

11. Copyright © 2015 Henry Exham
• Disaccharides are made up of two
monosaccharides that have been joined
together by a glycosidic bond.
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1.1 Carbohydrates
Disaccharides
Disaccharide Monosaccharides Found in
Maltose α-glucose + α-glucose Germinating seeds
Sucrose α-glucose + fructose Sugar cane (table sugar)
Lactose α-glucose + β galactose Milk

12. Copyright © 2015 Henry Exham
• A condensation reaction occurs in order to form a
glycosidic bond between two monosaccharides.
• For example here are two α-glucose molecules.
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1.1 Carbohydrates
Disaccharides
O
HH
OH
HO
1
23
4
5
6
O
HH
OH
HO
1
23
4
5
6
• In a condensation reaction water is removed to form the
bond.
• In this case this would form a 1,4-glycosidic bond because it is
between carbon 1 on one molecule and 4 on the other.
O
HH
HO
1
23
4
5
6
O
HH
OH
O
1
23
4
5
6

13. Copyright © 2015 Henry Exham
• You can do the opposite reaction to split
disaccharides into monosaccharides.
• This is called a hydrolysis reaction and water is put in.
13
1.1 Carbohydrates
Disaccharides
O
HH
HO
1
23
4
5
6
O
HH
OH
O
1
23
4
5
6
O
HH
O
HH
O
1
23
4
5
6
O
HH
OH
HO
1
23
4
5
6
HydrolysisCondensationH2O H2O

14. Copyright © 2015 Henry Exham
• If you continue joining together
monosaccharides with glycosidic bonds you
can make very long chains of sugars.
• Thee are called polysaccharides.
14
1.1 Carbohydrates
Polysaccharides
• They are perfect for storing sugar in a cell
because:
– They are insoluble so do not affect water potential
in the cell.
– They are compact and take up little space.

15. Copyright © 2015 Henry Exham
15
1.1 Carbohydrates
Polysaccharides

16. Copyright © 2015 Henry Exham
STARCH
• Starch is the energy store used by plants.
• When the plant makes glucose in
photosynthesis it stores it as starch because
starch is insoluble and compact.
• Starch is made up of two compounds.
– Amylose
– Amylopectin
16
1.1 Carbohydrates
Polysaccharides

17. Copyright © 2015 Henry Exham
STARCH-Amylose
17
1.1 Carbohydrates
Polysaccharides
AMYLOSE
Made of between 200-5000 α-
glucose molecules all joined by
1,4-glycosidic bonds.
This causes the molecules to coil
up into a spiral.

18. Copyright © 2015 Henry Exham
STARCH-Amylopectin
18
1.1 Carbohydrates
Polysaccharides
AMYLOPECTIN
Branched polymer of α-glucose made up
from a combination of 1,4-glycosidic
bonds and 1,6-glycosidic bonds.
This branching changes
the properties of the
molecule.
The side chains can be
easily broken off when
energy is required.

19. Copyright © 2015 Henry Exham
GLYCOGEN
19
1.1 Carbohydrates
Polysaccharides
GLYCOGEN
This is the energy store for animals and
fungi.
Made of many α-glucose molecules and
a combination of 1,4-glycosidic bonds
and 1,6-glycosidic bonds.
Basically the same as
amylopectin but with even
more branching!

20. Copyright © 2015 Henry Exham
CELLULOSE
• You have probably come across cellulose
before when learning about plant cells.
• It is a very strong substance used for making
cell walls.
• In order to achieve this is has a very specific
structure.
20
1.1 Carbohydrates
Polysaccharides

21. Copyright © 2015 Henry Exham
CELLULOSE
• Made of β-glucose molecules joined by 1,4-glycosidic
bonds.
• Alternate molecules are inverted so the bonding can
take place.
• Because of the glycosidic bonds pointing up and then
down it makes a straight chain rather than a coil like
in amylose.
21
1.1 Carbohydrates
Polysaccharides

22. Copyright © 2015 Henry Exham
CELLULOSE
• But also because of this the strands can form cross-
links with other strands.
22
1.1 Carbohydrates
Polysaccharides
=Hydrogen bonds
• These cross links are made from hydrogen bonds and
they give cellulose its great strength.

23. Copyright © 2015 Henry Exham
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