1. 1.0 MOLECULES OF LIFE BY : MDM. NURFAZLINI ISMAIL (MDM FAZ)
1.1 Water
1.2 Carbohydrates
1.3 Lipids
1.4 Proteins
1.5 DNA and RNA molecules
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1.1 WATER
At the end of this topic, students should be able to :
Explain the structure of water and properties of water molecule.
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4. Molecular Structure Of Water
Water is composed of :
2 hydrogen atoms and 1 oxygen atom.
The chemical formula is H2O.
Each H is linked to O by a single covalent bond.
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Covalent bond
Hydrogen
atoms
Oxygen atom
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Water is a polar molecule.
One end (oxygen) is slightly negative
One end (hydrogen) is slightly positive
Oxygen is more electronegative than hydrogen.
Tends to attract more electrons.
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The bond angle between the hydrogen and the oxygen is 104.5o
Producing an electric dipole.
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Polarity allows water molecules to form hydrogen bonds with each other
The slightly negative regions of one water molecule are attracted to the slightly positive regions of nearby water molecules, forming hydrogen bonds.
Each water molecule can form hydrogen bonds with up to four neighbors.
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Covalent bond
Hydrogen bond
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12. H O H  – Hydrogen bond  +  –  +  –  +  –  + —— —— Fig. 3-2
Figure 3.2 Hydrogen bonds between water molecules
 +

13. Properties Of Water Molecule
Universal Solvent ( Polar Molecule)
Low Viscosity
High Specific Heat Capacity
High Latent Heat of Vaporization
High Surface Tension
Maximum Density at 4⁰C
Due hydrogen bonding between polar water molecules
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1.2 CARBOHYDRATES
At the end of this topic, students should be able to :
State the classes of carbohydrates such as monosaccharides, disaccharides and polysaccharides.
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An organic compound containing the elements carbon, hydrogen, and oxygen.
(CH2O)n ; n = no. of carbon atom.
Most abundance class of organic compound.
Three main classes of carbohydrates:
Monosaccharides
Disaccharides
Polysaccharides
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Monosaccharides
Monosaccharide composed of one sugar unit.
Glucose (C6H12O6) is the most common monosaccharide.
Monosaccharides serve as :
major energy source for cells.
Component in the synthesis of other compound.
Major nutrients for cell.
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Monosaccharides molecule contain carbonyl group (-C=O) at only one of C atom and hydroxyl groups (-OH) at all another C atom.
Monosaccharides are classified by
The location of the carbonyl group (as aldose or ketose)
The number of carbons in the carbon skeleton
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19. (a) α and β glucose ring structures
Figure 5.7 Starch and cellulose structures
(a) α and β glucose ring structures

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Disaccharides
A disaccharide is formed when two monosaccharides joined by a glycosidic linkage.
Glycodisic linkage is a covalent bond formed by a condensation reaction between two MS.
Condensation reaction involves the removal of H atom from one sugar and –OH group from another (removal of a water molecule)
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Main disaccharides:
Maltose (glucose + glucose)
Sucrose (glucose + fructose)
Lactose (glucose + galactose)
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22. (a) Dehydration reaction in the synthesis of maltose
1–4
glycosidic
linkage
Glucose
Glucose
Maltose
(a) Dehydration reaction in the synthesis of maltose
1–2
glycosidic
linkage
Figure 5.5 Examples of disaccharide synthesis
Glucose
Fructose
Sucrose
(b) Dehydration reaction in the synthesis of sucrose

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Polysaccharides
Polysaccharides, the polymers of sugars, have storage and structural roles
The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
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POLYSACCHARIDES
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25. Storage polysaccharides
Both made up of α glucose monomers.
Starch
A storage polysaccharide of plants
Plants store surplus starch as granules within chloroplasts and other plastids
Glycogen
Is a storage polysaccharide in animals
Humans and other vertebrates store glycogen mainly in liver and muscle cells
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26. (a) Starch: a plant polysaccharide
Chloroplast
Starch
Mitochondria
Glycogen granules
0.5 µm
1 µm
Figure 5.6 Storage polysaccharides of plants and animals
Amylose
Glycogen
Amylopectin
(a) Starch: a plant polysaccharide
(b) Glycogen: an animal polysaccharide

27. Structural polysaccharides
The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch, cellulose is a polymer of glucose, but made up of β glucose
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28. Cell walls Cellulose microfibrils in a plant cell wall Microfibril
Fig. 5-8
Cell walls
Cellulose
microfibrils
in a plant
cell wall
Microfibril
10 µm
0.5 µm
Cellulose
molecules
Figure 5.8 The arrangement of cellulose in plant cell walls
Glucose
monomer

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1.3 LIPIDS
At the end of this topic, students should be able to :
State the types of lipids: triglycerides (fat & oil), phospholipids and steroids.
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31. General Features of Lipids
Lipids contain C, H and O but have a much smaller proportion of oxygen compared to a molecule of carbohydrate
The ratio of 0 : H is lower than carbohydrates.
The C-H bond is stronger than those in carbohydrates.
Stores large amount of energy.
Release higher energy when broken down
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Types of lipids
Triglyceride (fats and oil)
Triglycerides are constructed from two types of smaller molecules: glycerol and fatty acids
Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon
A fatty acid consists of a carboxyl group attached to a long carbon skeleton
In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triglyceride
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33. Fatty acid (palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
Figure 5.11 The synthesis and structure of a fat, or triacylglycerol
(b) Fat molecule (triacylglycerol)

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Phospholipid
In a phospholipid, two fatty acids and a phosphate group are attached to glycerol
The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head
Phospholipids are the major component of all cell membranes
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35. Choline Phosphate Hydrophilic head Glycerol Fatty acids
Hydrophobic tails
Figure 5.13 The structure of a phospholipid
(a)
Structural formula
(b)
Space-filling model

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Steroids
Steroids are lipids characterized by a carbon skeleton consisting of four fused rings
Cholesterol, an important steroid, is a component in animal cell membranes
Although cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease
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37. Figure 5.15 Cholesterol, a steroid

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1.4 PROTEINS
At the end of this topic, students should be able to :
Describe the basic structure of amino acids
State how amino acids are grouped
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39. General features of Protein
The monomer is amino acids.
Amino acids are organic molecules with carboxyl and amino groups, a hydrogen atom and R group side chain.
All are covalently linked to the same carbon atom
Amino acids are amphoteric molecules.
have both acidic (-COOH) and basic (-NH2 )
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Amino acids differ in their properties due to differing side chains, called R groups
R groups:
Non-polar hydrophobic
Polar hydrophilic
Electrically charged
Basic
Acidic
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NON-POLAR AMINO ACID
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POLAR AMINO ACID
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ELECTRICALLY CHARGED
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1.5 DNA AND RNA MOLECULE
At the end of this topic, students should be able to :
State the structures of nucleotide as the basic composition of nucleic acids (deoxyribonucleic acid, DNA and ribonucleic acid, RNA)
State the types of RNA
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46. Structure of nucleotide
Nucleotide is the basic unit for nucleic acids.
Polynucleotide is made of nucleotides
There are two types of nucleic acids:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
mRNA
tRNA
rRNA
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Nitrogenous bases
Pentose sugar
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48. (c) Nucleoside components: sugars
Deoxyribose (in DNA)
Ribose (in RNA)
Figure 5.27 Components of nucleic acids
(c) Nucleoside components: sugars

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There are two types of nitrogenous bases:
Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring
Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring
In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose
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50. (c) Nucleoside components: nitrogenous bases
Pyrimidines
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Purines
Figure 5.27 Components of nucleic acids
Adenine (A)
Guanine (G)
(c) Nucleoside components: nitrogenous bases