BIOLOGY FORM 4 CHAPTER 4 - CHEMICAL COMPOSITION OF THE CELL PART 1

1. BIOLOGY FORM 4
CHAPTER 4

2. The Chemical Basis of Life
Living organisms
are composed of
about
25 chemical
elements

3. An element is a pure substance
containing only one kind of atom

4. C, H,O, N:
make up the
bulk of living
matter

5. Functions of elements
in animal cells and plant cells
ELEMENT FUNCTION
H, C, O, N Synthesis of organic
compounds – lipid,
protein
SULPHUR A component of some
protein
SODIUM (Na) Regulates osmotic
pressure in cells
Help transmission of
nerve impulses

6. Chemical elements
– Combine in fixed ratios to form
compounds
Sodium Chlorine
Sodium
chloride
(table salt)

7. Compounds are molecules
containing more than one
type of element.
C6H12O6

8. COMPOUNDS
 substance which consists of two or more
elements chemically combined in a fixed ratio
Compound
Organic compound Inorganic compound
IN LIVING MATTER
chemical compounds which
contain C and H
Eg. Carbohydrates, protein,
lipid
NON LIVING MATTER,
do not contain C
Eg. water, acids, bases, mineral
– not synthesised by cell
– obtained from external
environment

9. CHEMICAL COMPOUNDS IN THE CELL
Carbohydrates C, H, O
Protein C, H, O, N, S, P
Nucleic acid C, H, O, P, N
Water H, O

10. The importance of chemical compounds in the cell
Carbohydrates - Primary source of energy
1g – 17 kJ of energy
- Starch – food storage in plant cells
- Glycogen – food storage in animal and plant
tissues
- Cellulose – constituent of cell wall
Lipids - Fats and oil –source of energy
1g - 38 kJ of energy
- Layer of adipose tissue - insulation, protection
- Major constituent for plasma membrane
- Prevent water loss in plants (cuticle)
- Steroid – cholesterol, oestrogen, progesterone

11. The importance of chemical compounds in the cell
Protein - Build new cells, renew damaged tissues
- Synthesis of enzymes, antibodies,
hormones
- Component of plasma membrane
- Synthesis of haemoglobin
Nucleic
acids
- Store genetic information
- DNA, RNA

12. Nucleic Acids
 Nucleic acids - DNA (deoxyribonucleic acid)
and RNA (ribonucleic acid), are made
from monomers known as nucleotides.
 Each nucleotide has three components: a 5-carbon
sugar, a phosphate group, and a nitrogenous base.
 If the sugar is deoxyribose, the polymer is DNA.
 If the sugar is ribose, the polymer is RNA.
Nucleotide

13. NUCLEIC ACID – DNA & RNA

14. 4
nitrogenous
bases
A pairs with T
C pairs with G

15. Differences between DNA & RNA
DNA RNA
Double stranded
polynucleotide (double
helix twist)
Single stranded
polynucleotide
Found in the nucleus,
chloroplast &
mitochondrion.
Found in the cytoplasm,
ribosomes & nucleus
Contains genetic
information about an
organism.
Copies information in DNA
for protein synthesis.
Sugar - deoxyribose Sugar - ribose

16. WATER
(H2O)

17. Water and Life
The most abundant substance
in living systems
%
70
of earth’s surface
Human body = 65%
Plants = 80%
Fruits and Vegetables = 70-80%

18. H2O

19. Water is considered a polar molecule.
– It has a positive and negative end.

20. The hydrogen end of the water molecule
has a slight positive charge (delta +).
The oxygen end of the
water molecule has a
slight negative charge
(delta -).

21. Why is the water molecule said to be bipolar?
Due to the presence of a pair of electric charges
equal in magnitude but opposite polarity,
separated by some distance

22. All living organisms are dependent on
water.
The structure of water is the basis for its
unique properties.
The most important property of water is
the ability to form hydrogen bonds.

23. Importance of water
in the cell

24. WATER :
 a vital chemical of living cells
 makes up 60 - 95% of the fresh
mass of an organism
Fresh mass = mass of cells + water
Dry mass = mass of cells

25. WATER:
universal solvent for many
biological molecules
is a medium for
diffusion

26. WATER: Medium for biochemical reactions.
- breaking down proteins, lipids carbohydrates
- photosynthesis
photosynthesis

27. WATER:
- Transport medium in blood, lymphatic, excretory,
digestive systems and vascular tissue of plants.

28. Water : Aid lubrication
 mucus, synovial fluid consist of
water
 mucus – assist movement of food
substances – intestinal tract
 synovial fluid – ease movement of
joint

29. WATER:
- gives support in hydrostatic skeletons e.g. in
earthworms.
TS earthworm

30. WATER:
- is needed by plant cells for cell enlargement, the
guard cell mechanism , cell turgidity & support in
plants.

31. WATER:
- has a cooling effect - sweating and panting
in animals and transpiration in plants

32. WATER:
- needed for seed germination - testa
swells and splits after water is imbibed

33. Water: Maintaining osmotic balance
- dissolved inorganic salts in water maintain the
osmotic balance in animal blood and interstitial
fluid

34. Water: Providing moisture
- respiratory gases – dissolve in moist alveolus –
before diffusing – blood capillaries

35. Water: High
surface tension
and cohesion
- maintain a
continuous flow
of water up the
the stem to the
leaf

36. Animals get water from:-
1. Drinking
2. Eating
3. Chemical reactions e.g.
respiration
food
O2
H2O
ATP

37. Elements in macromolecules & the percentage
dry mass of each macromolecule in a cell
Macromolecule Elements
% dry mass of a
cell
Carbohydrates CHO 15
Lipids CHOP 10
Proteins CHONS 50
Nucleic acids CHONP 18

38. CARBOHYDRATES

39. CARBOHYDRATES
 contain the elements:
 Carbon
 Hydrogen
 Oxygen
 Ratio H:O = 2:1
 Glucose:
 is the simplest carbohydrate (C6 H12 O6)

40. Easy to remember elements:
Food Elements
Carbohydrates C, H, O
Lipids C, H, O
Proteins C, H, O, N [sometimes
S and P]

41. Food rich in carbohydrates

42. Uses of carbohydrates:-
a) provide energy (17kJ/g)
Sugar in energy drink
equivalent to six pastries.

43. Uses of carbohydrates:-
c) to build cell walls in
plants
Cell wall
b) to store energy
e.g. starch in
potatoes or roots
Storage
organs

44. Uses of carbohydrates:-
d) fibre is important to prevent constipation
Food sources of fibre:
whole wheat, bran, fresh or
dried fruit & vegetables.
Constipated!!

45. Carbohydrates
Carbohydrates – 3 types
Monosaccharide Disaccharides
polysaccharides
Simple sugar
Glucose
Fructose
galactose
Maltose
Sucrose
lactose
starch cellulose glycogen

46. MONOSACCHARIDES
Simple sugar (C6H12O6)
Function : Main source of energy
SOURCE OF MONOSACCHARIDE:
Glucose – plants, fruits
Fructose - sweet fruits, honey
Galactose - milk
 All monosaccharides taste sweet, able to crystalline, water
soluble. Reducing sugars.

47. Disaccharides
- Consist of two monosaccharide joined together through
condensation
Condensation = process which involves removal of a water molecule
when a bond is formed between 2 molecules of monosaccharides
condensation
Glucose + glucose Maltose + water
condensation
Glucose + fructose Sucrose + water
condensation
Glucose + galactose Lactose + water
 All disaccharides taste sweet, able to crystalline, water soluble

48. FORMATION OF DISACCHARIDE
THROUGH CONDENSATION

49. Disaccharides
 Hydrolysis – chemical reaction that involves the breaking up
large molecules by adding water
hydrolysis
Maltose + water Glucose + glucose
hydrolysis
Sucrose + water Glucose + fructose
hydrolysis
Lactose + water Glucose + galactose
Sources of dissaccharides:
 Maltose – malt sugar
 Sucrose – cane sugar
 Lactose – milk sugar

50. BREAKING DOWN OF DISACCHARIDE
THROUGH HYDROLYSIS

51. Sweet & Soluble
& reducing sugar
(except sucrose)
Monosaccharides
Disaccharides
Polysaccharides
Not sweet & Insoluble
& non-reducing sugar

52. Polysaccharides
- Consist of hundreds of monosaccharides joined together
through condensation.
polysaccharides
starch cellulose glycogen
Found in Animals &
yeast
Main carbohydrate
reserve in plants
Component of cell
wall of plants
Found in Plants
Main carbohydrate reserve
in animals & yeast

53. In what form are excess carbohydrates stored?
1) in plants:
starch
2) in animals:
glycogen
Name two places
in animals where
glycogen is stored.
Liver & muscles

54. Cellulose: is the main source of dietary fibre
Explain why although humans cannot digest
dietary fibre, it is still important.

55. Functions of roughage:-
1. adds bulk to the contents of the intestine
and keeps food moving along the gut
Gut

56. Functions of roughage:-
2. prevents constipation as fibre retains water
so that the faeces are soft
3. prevents cancer of the colon (part of the
intestine)
faeces

57. Name the monosaccharide which forms
starch, glycogen and cellulose.
Glucose
Glycogen Cellulose Starch

58. How do starch, glycogen and cellulose
differ?
The way glucose units
are linked together
Glycogen Cellulose Starch

59. Polysaccharides
Polysaccharides + Water hydrolysis Monosaccharides
condensation
Hydrolysis : Adding diluted acid or through enzymatic
reaction

60. Question:
Where in a plant would you expect to find:
i) Cellulose (1)
ii) Starch (1)
i) Cellulose – found in cell walls of plant cell
ii) Starch – found stored in roots /
storage organs

61. Question:
Give biological explanations for each
of the following statements:
The diet of athletes is usually high in
carbohydrates. (5)
Athletes need a lot of energy. Carbohydrates are
the body’s main energy source. Carbohydrates
like starch in bread are digested into glucose.
Glucose is used in respiration to release energy. If
athletes take in monosaccharides, i.e. sugars e.g.
glucose, they are provided with energy very
quickly.

62. Why is the tired athlete choosing sugar
rather than starch?
Sugars, especially
monosaccharides can
be used for respiration
right away.
Starch needs to be
digested first.

63. LIPIDS

64. LIPIDS
 a name for fats and oils
 contain the elements:- C, H, O
 Ratio H:O > 2:1
lard

65. Lipids are:
water-insoluble organic substances but
readily soluble in organic solutions e.g.
ether

66. Water is so attracted to other water molecules
that anything between them is squeezed out of
the way.
‘’;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;

67. Food rich in lipids:-
Nuts
Egg yolk

68. Types of Lipid
1. Triglycerides [Fats & Oils]
2.Waxes
3.Phospholipids
4. Steroids

69. Types of Lipid
1. Triglycerides
[Fats & Oils]
1. Waxes
2. Phospholipids
3. Steroids

70.  building blocks of a lipid molecule:
 1 Glycerol
 3 Fatty acids
A molecule of fat

71. Synthesis of a Fat

72. Formation of Triglyceride
Formation – condensation
Breakdown - Hydrolysis

73. LIPID CONDENSATION

74. LIPID HYDROLYSIS

75. What is the difference between a fat and an oil?
 fats - solid at 20C
 oils - liquid at 20C

76. Animal fat solidifies at a low
temperature

77.  excess lipids are stored:-
1) in the ADIPOSE TISSUE under the skin
2) around organs
Fat around
heart.

78. Functions of Triglycerides
1. Store energy in animals +
Yield energy

79.  uses of lipid
a) provide energy (38 kJ/g)
b) store energy

80. Comparison of energy yield from:
Triglycerides: 37 kJ g-1
Carbohydrates: 17 kJ g-1
MORE energy from
triglycerides:
Due to more hydrogen.

81. Question:
Explain why one kilogram of starch crops
releases less energy when burnt, compared to
one kilogram of oil crops. (2)
Starch is a carbohydrate whilst oil is a lipid.
Carbohydrates have a lower energy content
than lipids.

82. 2. Animals store extra fat when
hibernating: acts as an insulator.
Subcutaneous fat

83. 2. Fat around organs:
 protect against bumps
 keeps them warm
Kidney surrounded
by fat

84. 3. In aquatic mammals blubber contributes
to buoyancy.

85. Test for Triglycerides
Paper becomes
translucent.

86. Chemical Test for Triglycerides
Sudan III

87. Chemical Test for Triglycerides
Emulsion Test

88. Types of Lipid
1. Triglycerides [Fats & Oils]
2.Waxes
3. Phospholipids
4. Steroids

89. Waxes: not a food source
no enzymes to break them down

90. Feathers do not
get wet – WHY?
Raindrops on
feathers.

92. Waxes are mainly for
e.g.
cutin makes up the
waxy cuticle of leaves
fruits produce a
waxy coating to
keep from drying
out

93. sebum in mammalian skin

94. wax in ears traps:
dust
sand
other foreign
particles
do not go deeper into the
ear and cause no damage

95. suberin in Casparian strips,

96. exoskeleton in insects
[contains wax]

97. waxes build elaborate structures such
as beehives

98. Types of Lipid
1. Triglycerides [Fats & Oils]
2.Waxes
3.Phospholipids
4. Steroids
5. Glycolipids
6. Lipoproteins
7. Terpenes

99. Phospholipids
• lipids with a phosphate group

100. • constituents of membranes

101. Types of Lipid
1. Triglycerides [Fats & Oils]
2. Waxes
3. Phospholipids
4.Steroids

102. Steroids
are structurally different from all other
lipids
consist of a complex carbon ring
structure
Cholesterol is a steroid.

103. Cholesterol:
• is the steroid present in the
largest amount in humans
• an important constituent of
animal plasma membranes
made in the
liver

105. Sex hormones are
Steroids

106. Why are fats and oils classified as
triglycerides?

107. C16H32O2
R
- fatty acids may be:
 saturated or
unsaturated

108. Saturated fatty acid
[Single bonds only]
Unsaturated fatty acid
[Double bonds]

109. Saturated & Unsaturated Fat
• Fats with saturated fatty acid = Saturated Fat
eg butter (solid at room temperature)
• Fats with unsaturated fatty acid = Unsaturated
Fat eg. Corn oil (liquid at room temperature)
Saturated Fat

110. Saturated & Unsaturated Fat
• Unsaturated fat with 1 double bond =
Monounsaturated fat
• Unsaturated fat with more than 1 double bond =
Polyunsaturated fat

111. Difference between saturated fats &
unsaturated fats
Saturated fats Differences Unsaturated fats
None The presence of
double bonds
between carbon
atoms in fatty acids
Minimum one
No Ability to react with
an additional
hydrogen atom
Yes
Solid Condition at room
temperature
Liquid
Increase Cholesterol level Decrease
Butter Examples Corn oil

113. Proteins are of primary importance
to the life of the cell
• by dry weight proteins are the major
components of an actively growing cell

114. PROTEINS
 contain the elements:-
 C, H, O, N (sometimes S
and P)
 food rich in proteins:-
 Meat
 Fish
 Egg white
 Cheese

115.  Uses of proteins:-
1. for growth
2. for cell repair and replacement
3. to make enzymes
4. to make antibodies

116. What are the building blocks
of proteins called?

117. How do we get the amino acids
needed to build proteins?
EATING Protein-Rich
Foods

118. Proteins ingested are digested by
enzymes called…p…r…ot…e…as…e…s …

119. From amino acids to proteins
two amino acids dipeptide
three amino acids tripeptide
more than 50 amino
polypeptide
acids
6 000-1000 000 protein

120. Amino Acid + Amino Acid --> Dipeptide
Amino Acid + Dipeptide --> Tripeptide
A.A. + A.A. + …..+ Tripeptide --> Polypeptide

121. Structure of an
amino acid
molecule

122. R = Side group/chain [varies]
What is an ‘amino acid’?
An organic molecule possessing both carboxyl
and amino groups

123.  Two amino acids are linked by a:
Peptide bond
 Polypeptide: many amino acids are linked

124.  A protein: many polypeptides joined up

125. different amino acids occur in proteins

126. Let us discover how
two amino acids
link together

127. H2N
Amino acids are joined together by a
H
condensation reaction
Carboxyl
group
C C
H
O
OH
N
H
C C
CH3
O
OH
H2N
H
C
H
O
H H
C N C C
CH3
O
OH
Peptide
bond
Amino
group
H
H
+
H2O
A peptide bond is formed by condensation
between the -NH2 of one amino acid and -COOH
of another

128. AMINO ACID CONDENSATION

129. DIPEPTIDE HYDROLYSIS

130. Many amino acids joined together =
N-terminus
H
H H O H H O H H O H H O H H O
N C C N C C N C C
H CH3
CH2
OH
N C C
CH2
C
O
OH
N C C
CH2
CH
CH3 H3C
C-terminus
CH2
OH
H H O
N C C
H H O
N C C
H H O
N C C
CH2
SH
OH
Polypeptide chain

131. A protein molecule:
 contains 100’s and 1000’s of amino acids joined
together by peptide links into one or more
chains
3 chains in collagen (in mouse tail)

132. Polypeptide chains can be folded
in various ways

133. Proteins are unbranched, not like
carbohydrates
Branched
molecule
Unbranched
Protein molecule

134. Many different types of proteins
exist. How can this be?
MILLIONS of
Antibodies exist
A LARGE NUMBER
OF ENYZMES

135. Because any of 20 different amino
acids might appear at any position
• E.g. a protein containing 100 amino acids
could form any of 20100 different amino acid
sequences
• this is 10130, i.e. 1 followed by 130
zeros

136. Number and Sequence of amino acids
determine the protein
6 amino acids
5 amino acids
7 amino acids
6 amino acids but in
a different
sequence

137. Test for Protein: Biuret Test
Protein
present

138. Test for Protein: Biuret Test
Cheese is rich
in protein.
Add an equal amount of
NaOH to the solution
followed by 1-2 drops of
CuSO4 solution
pestle
mortar

139. When a protein reacts with copper(II) sulfate
(blue), the positive test is the formation of a
violet colored complex.
Purple / Lilac:
Positive test

140. Proteins have many functions:
enzymes
hormones
structural
proteins
What dictates the function of each protein?
The exact sequence of amino acids.

141. DNA contains the information that
determines the sequence of amino acids

142.  Two types of amino acids:
1. Essential [8 amino acids]
must be eaten as they
cannot be made by the
body
2. non-essential
can be made by the
body

143.  contain all the essential amino acids
 Source: animals : eggs, meat, fish, cheese
 deficient in one or more essential amino acid
 Source: plants

144.  For example, corn is deficient in one
amino acid
 Individuals who eat only corn would show
symptoms of protein deficiency.
• This is true from any diet limited to a
single plant source, including:
 Rice
 Wheat
 or potatoes

145.  are an exception:

146. How can protein deficiency from a vegetarian
diet be avoided?
By eating a
combination of plant
foods that complement
each other to supply all
essential amino acids.

147.  For example, beans supply the lysine that
is missing in corn, and corn provides
the methionine which is deficient
in beans.

148. Excess proteins:
 cannot be stored in the body
 are broken down in the liver by a process
called DEAMINATION
 the waste product produced is called UREA
liver

149. Structure of a Protein
• four levels of organisation exist:-
1) Primary structure
2) Secondary structure
3) Tertiary structure
4) Quaternary structure

150. Structure of a Protein

151. Primary structure of a
protein:
 the number and sequence of
amino acids held together
by peptide bonds in a
polypeptide chain
 the primary structure of each
type of protein is unique

152. Secondary structure:
• the way in which the polypeptide is arranged
in space

153. Two common secondary structures are
the:
 -helix
 -pleated sheet
• bonds
present:
1. Peptide
2. Hydrogen

154. Tertiary structure:
• is when the polypeptide
chain bends and folds
extensively to form a
precise compact
• is a complex, three-dimensional shape that
determines the final configuration of the
polypeptide

155. The joining of more than one polypeptide chain
leads to the quaternary structure of proteins

157. Quaternary structure occurs in many highly
complex proteins
A huge variety of quaternary structures exist

158. Denaturation
of Protein

159. The loss of the specific three-dimensional
conformation (secondary structure) of a protein
A protein spontaneously refolds into its original
structure under suitable conditions

160. How long can the change be?
Temporary or permanent.
Is the amino acid sequence affected?
Remains unaffected.

161. Why is denaturation of proteins
considered as harmful to an
organism?
The molecule unfolds and cannot
perform its normal biological
functions.

162. Denaturation agents can be:
i) Heat
ii) Strong acids & alkalis and high
concentrations of salts
iii) Heavy metals (e.g. mercury)
iv) Organic solvents and detergents

163. i) Heat
- weak hydrogen bonds and non
polar hydrophobic interactions
are disrupted
- Why?

164. Heat increases the
kinetic energy
Causes the molecules
to vibrate so rapidly
and violently that
bonds break

165. protein
coagulates

166. ii) Strong acids & alkalis + high
concentrations of salts
ionic bonds are
disrupted
the protein is
coagulated

167. Coagulation of milk by adding salts

168. Breakage of peptide bonds may occur if the
protein remains in the reagent for a long time

169. iii) Heavy metals
cause the protein to precipitate out of the
solution
Cations (+) form strong bonds with carboxylate anions
(COOH-) and often disrupt ionic bonds

170. iv) Organic solvents & detergents
disrupt hydrophobic
interactions
form bonds with non-polar
groups
this in turn disrupts
intramolecular H-bonding

171. Why does the solution become purple when
beetroot discs are placed in detergent?
1. Proteins in cell membrane & tonoplast are
denatured.
2. Phospholipid bilayer is damaged.

172. Why is the skin wiped with alcohol before an
injection is given?
Alcohol is used as a disinfectant.
It denatures the protein of any
bacteria present on the skin.

174. Food Test
Colour
change
Starch + iodine solution Yellow to blue
black
Iodine
solution
Starch

175. Look at this picture.
Is starch present in potato? Yes.

176. Food Test
Colour
change
Protein
(Biuret test)
+ sodium hydroxide solution +
1-2 drops of copper sulfate
solution
Blue to purple
1. Sodium
hydroxide
2. Copper solution
sulfate
solution
Egg white
[protein]

177. A positive test for
protein was obtained
for…a…lb…u…m…in…

178. Food Test
Colour
change
Oil
+ ethanol + shake + water +
shake
A white emulsion
forms

179. Food Test
Colour
change
Oil rub food onto a dry piece of
filter paper
A greasy spot
forms

181. Food Test
Colour
change
Glucose + Benedict’s solution or
Fehling’s solution + heat
Blue to brick red
or orange

182. Food Test
Colour
change
Glucose + Benedict’s solution or
Fehling’s solution + heat
Blue to brick red
or orange

183. Food Test
Colour
change
Starch + iodine solution Yellow to blue
black
Protein
(Biuret test)
+ sodium hydroxide solution +
1-2 drops of copper sulfate
solution
Blue to purple
Oil
1) + ethanol + shake + water +
shake
1) rub food onto a dry piece of
filter paper
A white emulsion
forms
A greasy spot
forms
Glucose + Benedict’s solution or
Fehling’s solution + heat
Blue to brick red
or orange

184. When the food to be tested is a solid:
1. Crush the food with some water using a
pestle and a mortar.
2. Filter.
3. Add the reagents to the filtrate.
pestle
mortar

185. Credits to Dr Marthese Azzopardi

186. THE END