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Unit 1.1 Molecules
Biology Department
Watford Girls Grammar School
Introduction
 For
each of the following you should be
able to:
 Describe the properties
 Know the general formulae & structure
 Understand the role in animals & plants
•Water
•Proteins
•Carbohydrates
•Nucleic acids
•Lipids
H +
Water
-
O
H
 Water
is a polar molecule
 It forms weak hydrogen bonds
 It remains a liquid over a wide
temperature range
 Water molecules stick to one another =
cohesion (surface tension)
 Water molecules stick to other
substances = adhesion (capillarity)
+
Water
has a high specific heat capacity – so
water can maintain a reasonably
constant temperature (homeostasis)
 It has a high latent heat of vaporisation
– so animals use water to cool
themselves
 It is less dense as a solid (ice)…
 … and ice is a poor conductor
 Water is a good solvent
 It
Carbohydrates


Contain the elements Carbon
Hydrogen & Oxygen
There are 3 types:



Monosaccharides
Disaccharides
Polysaccharides
Monosacharides
 (CH2O)n
 If
n=3, triose (glyceraldehyde)
 If n=5, pentose (fructose, ribose)
 If n=6, hexose (glucose, galactose)
 Monosaccharides are used for
 Energy
 Building
C
blocks
C
O
C
C
C
C
Isomerism
 They
can exist as isomers:
 &  glucose

OH
OH

Disaccharides
 Formed
from two monosaccharides
 Joined by a glycosidic bond
 A condensation reaction:
+ glucose  maltose
 glucose + galactose  lactose
 glucose + fructose
 sucrose
 glucose
Condensation reaction
C
C
C
O
C
C
C
C
C
C
O
OH
OH
C
C
C
Condensation reaction
C
C
C
O
C
C
C
C
C
C
O
OH
OH
C
C
C
Condensation reaction
C
C
C
O
C
C
C
C
C
C
O
O
H2O
C
C
C
Condensation reaction
C
C
C
O
C
C1
C
C
C
O
4C
O
C
C
A disaccharide
1,4 glycosidic bond
C
Polysaccharides
 Polymers
formed from many
monosaccharides
 Three important examples:
 Starch
 Glycogen
 Cellulose
Starch
Insoluble store of glucose in plants
formed from two glucose polymers:

Amylose
-glucose
1,4 glycosidic bonds
Spiral structure

Amylopectin
-glucose
1,4 and some 1,6
glycosidic bonds
Branched structure
Glycogen
 Insoluble
compact
store of glucose in
animals
 -glucose units
 1,4 and 1,6
glycosidic bonds
 Branched structure
Cellulose
 Structural
O
O
O
O
polysaccharide
in plants
 -glucose
 1,4 glycosidic bonds
 H-bonds link adjacent
chains
O
Lipids
 Made
up of C, H and O
 Can exist as fats, oils and waxes
 They are insoluble in water
 They are a good source of energy
(38kJ/g)
 They are poor conductors of heat
 Most fats & oils are triglycerides
Triglycerides
 Formed
by esterification…
 …a condensation reaction between 3
fatty acids and glycerol:
H
C
O H
Glycerol
H
C
O
H
H
C
O
H
Fatty acids
 Carboxyl
group (-COOH)
 attached to a long non-polar
hydrocarbon chain (hydrophobic):
H
O
C
O
H
H
H
C
H
C
H
C
H
H
C H
C
H
C
H
C
H
H
H
H
H
A saturated fatty acid (no double bonds)
O
C
H
H
C
C
H
O
H
H
H
C
H
C H
C
C
H
C
H
H
H
H
H
A monounsaturated fatty acid
O
C
O
H
H
H
H
C
C
C
H
H
H
C H
H
C
C
C
H
H
H
A polyunsaturated fatty acid
Esterification
H
C
O H
H
C
O
H
C
O
H
H
H
O
C
O
H
C
H
C
H
H
C
H
C
H
H
Glycerol
Fatty acid
H
Esterification
H
C
O H
H
C
O
H
C
O
H
H
H
O
C
O
H
C
H
C
H
H
C
H
C
H
H
Glycerol
Fatty acid
H
Esterification
H
C
O H
H
C
O
H
C
H
H
O
C
O
H
C
H
C
H
H
C
H
C
H
Glycerol
H
O
H
Fatty acid
H
Esterification
H
C
O H
H
C
O
H
C
H
H
O
C
O
Ester bond
H
O
H
water
H
C
H
C
H
H
C
H
C
H
H
Esterification
 This
happens three times to form a
triglyceride:
glycerol
fatty acids
Phospholipids
 One
fatty acid can be replaced
by a polar phosphate group:
hydrophilic
phosphate
glycerol
Hydrophobic fatty acids
Functions of lipids
 Protection
of vital organs
 To prevent evaporation in plants &
animals
 To insulate the body
 They form the myelin sheath around
some neurones
 As a water source (respiration of lipids)
 As a component of cell membranes
Proteins
Made from C H O N & sometimes S
 Long chains of amino acids
 Properties determined by the aa
sequence

Amino acids
~20 aa
 Glycine R=H
 Alanine R=CH3

R
O
H
H
N
amine
C
H
C
O H
carboxyl
Peptide bonding
H
H
R
N
C
H
C
O
O H
H
H
R
N
C
H
C
O
O H
Peptide bonding
H
H
R
N
C
H
C
O
O H
H
H
R
N
C
H
C
O
O H
Peptide bonding
H
H
R
N
C
H
C
O
H
H H
O
R
N
C
H
C
O
O H
Peptide bonding
H
H
R
N
C
C
O
H
H
R
N
C
H
C
O
O H
Peptide bond
H H
O
water
A condensation reaction
Peptide bonding
H
H
R
N
C
H
R
O
C
N
H
A dipeptide
C
H
C
O
O H
Primary structure
 The
sequence of aa is know as the
primary structure
 The aa chain is a polypeptide
Secondary structure
forms between the –COOH
and the -NH2 of adjacent aa
 This results in the chains folding:
 H-bonding
Secondary structure
-helix
-pleated sheet
Tertiary structure
 Bonding
between R-groups
gives rise to a 3D shape
 H-bonds =O HNaffected by temp & pH
 Ionic
bonds –NH3-COOaffected by pH
 Disulphide
bridge
--CH2S-SCH2affected by reducing agents
Quaternary structure
 Some
proteins have
more than one
polypeptide chain
 Each chain is held
together in a precise
structure
 eg Haemoglobin
Types of proteins
 Fibrous
proteins
 e.g.
collagen
 Insoluble
 structural
 Globular
proteins
 e.g.enzymes
 Soluble
 3D
shape
Functions of proteins
Enzymes –
 Transport –
 Movement –
 Cell recognition –
 Channels –
 Structure –
 Hormones –
 Protection –

Amylase
Haemoglobin
Actin & myosin
Antigens
Membrane proteins
Collagen & keratin
Insulin
Antibodies
Nucleic acids
 DNA &
RNA
 Made up of nucleotides:
phosphate
base
pentose sugar
Nucleotides
2
types of base:
 Pyrimidines
-
 Cytosine
C
T
 Thymine
 Purines
 Adenine
 Guanine
A
G
Complimentary base pairing
 Adenine
will only bind with Thymine
 Cytosine will only bind with Guanine
T
A
C
G
DNA structure
nucleotide
Condensation
polymerisation of the
deoxyribose nucleotides
Replication
 During
cell division the DNA must
replicate
 The DNA double helix unwinds
 The exposed bases bind to free floating
nucleotides in the nucleoplasm
 DNA polymerase binds the
complimentary nucleotides
 Replication is
semiconservative
The genetic code
 The
sequence of nucleotide bases
forms a code
 Each ‘code word’ has three letter – a
triplet code
 Each codon codes for a specific amino
acid e.g:
 GGG
= proline
 CGG = glycine
 ATG = tyrosine
 ACT = stop (no amino acid)
Protein synthesis
 The
DNA codes for
proteins
 A copy of DNA
(mRNA) is made in
the nucleus
(transcription)
 The mRNA is used
to make a protein
(translation) in the
cytoplasm
Transcription
 The
DNA polymerase
unwinds the DNA
 Free nucleotides join
onto complimentary
bases
 RNA polymerase links
adjacent nucleotides
 The completed mRNA
moves out of the
nucleus
Transcription
Amino acid activation
 transferRNA:
 tRNA binds
onto a
specific amino acid
Translation
 mRNA binds
to a ribosome
 tRNA carries an amino acid to the
ribosome
Translation
 A second
tRNA brings another aa
 The two aa’s bind
 The process repeats
Translation
 A polypeptide
chain forms
 Eventually a stop codon is reached
The Human Genome Project

A multinational project aimed at sequencing
the entire human genome
 Visit the Human Genome Web site:

www.ornl.gov/hgmis/project/about.html
 www.sanger.ac.uk
Acknowledgements

Animated cell models used by kind
permission of The Virtual Cell website:

Feel free to use this presentation for
educational non-profit making purposes.
Quiz

a)
b)
c)
d)
1. Which of the following is not an
important property of water
Its polar nature
Its low specific heat capacity
Its high latent heat of vaporisation
Its low density in solid form
Quiz

a)
b)
c)
d)
2. The general formula for a
monosaccharide is:
(CH2O)n
(CHO)n
C(H2O)n
C nH 2O n
Quiz

a)
b)
c)
d)
3. Sucrose is made up of
glucose + fructose
glucose + galactose
glucose + glucose
galactose + fructose
Quiz

a)
b)
c)
d)
4. Amylopectin is made up of:
-1,4 glycosidic bonds
-1,4 & -1,4 glycosidic bonds
-1,4 & 1,6 glycosidic bonds
-1,4 & 1,6 glycosidic bonds
Quiz

a)
b)
c)
d)
5. Formation of a triglyceride does
NOT involve:
A condensation reaction
Esterification
Polymerisation
A reaction between 3 fatty acids &
glycerol
Quiz

a)
b)
c)
d)
6. The general formula of a saturated
fatty acid is:
CnH2nO2
Cn(H2O)n
(CH2O)n
(CH2)nO
Quiz

a)
b)
c)
d)
7. Which of the following is not
responsible for a proteins tertiary
structure
ionic bonding
covalent bonding
hydrogen bonding
disulphide bonding
Quiz

a)
b)
c)
d)
8. Which of these is not an amino
acid:
alanine
cysteine
glycine
cytosine
Quiz

a)
b)
c)
d)
9. Which process involves tRNA:
transciption
translation
DNA replication
gene mutation
Quiz

a)
b)
c)
d)
10. The formation of RNA does not
involve:
ribose sugar
thymine
removal of water
phosphate