MOLECULE OF LIFE

BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

CHAPTER 1: MOLECULES OF LIFE

1.1 WATER

(a) STRUCTURE OF WATER MOLECULE

 A water molecule made up of one oxygen

atom and two hydrogen atoms (H2O).

 The water molecule has a bent shape with

bond angle 104.5°.

 Each hydrogen atom joined to the oxygen

atom by covalent bond (sharing electron)

 Water is a polar molecule because oxygen

and hydrogen atom of water molecule have

unequal distribution of electrons. (a) Structure of a water molecule
 Oxygen is more electronegative charge

than hydrogen. Thus, oxygen pulls

electron closer than hydrogen.
 Giving oxygen partial negative charge

(δ-) and hydrogen partial positive charge
(δ+)

 What is the effect of water polarity?
 Hydrogen bond form when partial
positive charge (δ+) of hydrogen atoms
attracted to partial negative charge (δ-) of

oxygen atoms of nearby water (b) Two water molecules joined together

molecules.
 Each water molecule can form hydrogen

bond with a maximum of four

neighboring water molecules.
 Hydrogen bond responsible for

unique properties of water.

(c) A water molecule forms hydrogen bonds
with four other water molecules.

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

1. Universal solvent (b) SIX PROPERTIES OF WATER
 Water able to dissolve many substances because it is able to
attract and surround the polar molecules. E.g.: NaCl.
 It is due to polarity of water.

2. Low viscosity *Hydration shell : The sphere of water molecules around a
(Viscosity: Measure of dissolved ion
resistance to flow or  Water has low viscosity (easy to flow or move due to low
measure of fluid friction)
resistance).
 It is due to hydrogen bonds between water molecules

continously break and reform.

3. High specific heat  Water has high specific heat capacity as a result of the
extensive hydrogen bond between its molecules.
capacity Its mean large amount of heat has to be absorbs or released by
water in order to change its temperature.
(Specific heat: The amount 

of heat that must be

absorbed or lost for 1 gram

of substance to change its

temperature by 1°C)

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

4. High latent heat of  Water has high latent heat of vaporisation because a lots of
heat must be absorbed to break the hydrogen bonds between
vaporisation liquid water before converted into vapor.

(Heat of vaporization: the

quantity of heat that a

liquid must absorb for 1

gram of water to be

converted to gaseous state/

vapors)

5. High surface tension  Water has higher surface tension than any other liquid.

(Surface tension: Measure  The forces involving water molecule:

of how difficult it is to i. Cohesive force/ cohesion

strecth or break the surface  Forces attraction between water molecule due to

of a liquid) hydrogen bonds
 Responsible for the water surface tention
 The unequal attraction cause inward forces that cause

high surface tension at the water surface, produces a

strong layer.

ii. Adhesive force/ adhesion
 Forces attraction between water molecule with other

molecules causes molecule stict together.

 At the surface, there are fewer
water molecules to cling to
since there is air above

 This results in a stronger bond
between those molecules that
actually do come in contact
with one another, and a layer
of strongly bonded water.

Diagram show water droplets

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

6. Maximum density at 4oC  Water has highest density at 4°C. As temperature decrease
from 4°C to 0°C, its density reduces (floating).

 Ice less dense than liquid water.

1.2 CARBOHYDRATES

(a) Classes of carbohydrates
THREE CLASSES OF CARBOHYDRATE
1. Monosaccharide
2. Disaccharides
3. Polysaccharides

(b) Monosaccharide, Disaccharide and Cellulose
1. MONOSACCHARIDE

 Simplest sugar with general formula (CH2O) n, where n is the number of atoms.
 Classified based on:

 Number of C atoms
(i) 3C = triose: glyceraldehyde, dihydroxyacetone
(ii) 5C = pentose: ribose, deoxyribose
(iii) 6C = hexose: glucose, galactose, fructose

 Location of carbonyl group on the C skeleton
(i) Aldose: carbonyl group at the end (glucose, galactose)
(ii) Ketose: carbonyl group in the middle between C (fructose)

 Main monosaccharides in human body is glucose
 Two forms of glucose that called as isomers are α-glucose and β-glucose

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014
α-glucose β-glucose

2. DISACCHARIDE

 Consist of two monosaccharide joined by glycosidic linkage through condensation
process.

 Disaccharides also can be separated into its monomer through hydrolysis process.
 Examples of disaccharides is maltose.

MALTOSE

3. POLYSACCHARIDE
 Polymers consisting of many monosaccharides linked by glycosidic linkage through

condensation process
 Example of polysaccharides is cellulose

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014
CELLULOSE

(c) CONDENSATION AND HYDROLYSIS
Condensation: A reaction in which two molecules are covalently bonded to each other with the
loss of a water molecule.

Hydrolysis: A reaction that breaks bonds between two molecules by the addition of water.

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

(d) THE FORMATION AND BREAKDOWN OF MALTOSE
Formation of maltose

 Two α-glucose are fused together between carbon no. 1 of one α-glucose with carbon
no. 4 of another α-glucose

 By condensation process
 Through elimination of one molecule of water
 Formation of α- 1,4 glycosidic linkage between two α-glucose

Breakdown of maltose

 Two α-glucose breaks between carbon no. 1 of one α-glucose with carbon no. 4 of
another α-glucose

 By hydrolysis process

 Through addition/using of one molecule of water
 Formation of two α-glucose

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

1.3 LIPIDS
(a) Types of lipids

Lipid is large molecule but not a polymer because not made up by repeating monomers. There
are three types of lipids that are:

Triglycerides THREE TYPES OF LIPIDS
 Made up of 1 glycerol and 3 fatty acids.
 Saturated fat is triglyceride with solid state at the room temperature.
 Unsaturated fat (oil) is triglyceride with the liquid state at room

temperature.

Phospholipids Made up of 1 glycerol, 2 fatty acids and 1 phosphate group

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

Phospholipid bilayer Micelle

Steroids  Made up of carbon skeleton with four interconnecting ring and
functional side chains

 Example : Cholesterol (a component of animal cell membrane)

Glycerol Structure of cholesterol

STRUCTURE OF GLYCEROL AND FATTY ACID
 A chain of three carbon atoms.
 Each of the carbon atoms bonded to hydrogen atoms and a hydroxyl

group (OH).

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

Fatty acid  General formula: R-COOH

 R is hydrocarbon chain. The characteristic of R is hydrophobic/ non-

polar.
 R causes the fatty acid become insoluble in water.
 R determined either the fatty acid is saturated or unsaturated fatty acid.

Saturated fatty acid Unsaturated fatty acid

Hydrocarbon chain no double Present of 1 or more double bonds
bonds// Hydrocarbon chain in hydrocarbons//Hydrocarbon chain
saturated with hydrogen atoms. not completely saturated with
hydrogen atoms.

Solid in room temperature Liquid in room temperature

Example; stearic acid Example; oleic acid

1.4 PROTEINS
(a) Basic structure of amino acids

AMINO ACID

 Amino acid is the monomer for

protein/ polypeptide
 An amino acid consists of:

 Amino group (-NH2)
 Carboxyl group (-COOH)
 Side chain (R group)
 α-carbon and a hydrogen atom

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

(b) Group of amino acids

 There are 20 amino acids which act as monomer for protein. Amino acid is classified into 4

groups according to their properties of the side chain.
 Group of amino acid: Non-polar, polar, acidic and basic.

Group Properties Example
Non-polar

Present of hydrophobic side chain.
Alanine, Glycine

Eg: - CH3

Polar

Present of hydrophilic side chain.
Asparagine, Serine

Eg: - OH

Acidic Present of carboxyl group in the Aspartic and glutamic acid
Basic side chain.

Eg:
-COO-

Present of amino group in the side Arginine
chain.

Eg: - NH3+

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

(c) Formation and breakdown of dipeptide

Formation of dipeptide

 Two amino acid bonds together through condensation process
 Involved removal of a water molecule
 Peptide bond form between carboxyl group of first amino acid and amino group of

second amino acid.
 Forming dipeptide

Breakdown of dipeptide

 Dipeptide break down its peptide bond to two amino acids
 by hydrolysis process
 Involve addition of a water molecule

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

1.5 DNA AND RNA MOLECULES

(a) Structures of nucleotide as the basic composition of nucleic acids
DNA AND RNA MOLECULES

DNA and RNA are types of nucleic acids that store/ carry genetic or hereditary information.
1. DNA (deoxyribonucleic acid)

Functions: Contains information that is essential for almost all cell activities, including cell
division.
2. RNA (ribonucleic acid)
Functions: Involves in protein synthesis

 DNA and RNA exist as polymers called Phosphoester Bond
Covalent bond
polynucleotides. Each polynucleotide
Phosphoester Bond
consists of monomers called nucleotides. Covalent bond
 Nucleoside is when nitrogenous base

combine with a pentose sugar only.
 A nucleotide, in general, is composed of

three parts:

i. Nitrogenous base
 purines (double ring - Adenine,

Guanine)
 pyrimidines (single ring -

Cytosine, Thymine, Uracil)

ii. Pentose Sugar (ribose in RNA while

deoxyribose in DNA)

iii. one phosphate groups
 In a nucleotide:

 phosphate group is joined to the 5th

C of pentose by phosphoester bond
 nitrogenous base is joined to the 1st

C of pentose by covalent bond

TYPES OF RNA

 RNA (ribonucleic acid)

- Involves in protein synthesis

- 3 types that are:

1. mRNA: Carries the genetic information from DNA to the ribosomes.

2. rRNA : Involved in translation of mRNA into protein.

3. tRNA : Carry amino acids to the ribosomes (rRNA) during translation process

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

COMPARISON BETWEEN DNA AND RNA
Similarities

1. Both monomer for DNA and RNA is nucleotide
2. Both contain pentose sugar
3. Both have phosphate group

Differences between DNA and RNA nucleotide

DNA RNA
Pentose sugar is deoxyribose Pentose sugar is ribose

Four bases are Four bases are
Adenine, Guanine, Cytosine, Thymine Adenine, Guanine, Cytosine, Uracil

Differences between DNA and RNA strand

DNA RNA
Consists of one polynucleotide strand/
Consist of two polynucleotide strands/ single stranded.
double strand
No double helix is formed.
The two strands coiled together to form a
double helix.

Can be found in the nucleus Can be found in the nucleus and cytoplasm

One type only Many types
Three types of RNA that involved in
DNA carries the genetic information of a protein synthesis are mRNA, tRNA and
cell rRNA.

The three types of RNA are important in
protein synthesis

More stable/permanent Less stable/non-permanent

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BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

Structure of DNA based on Watson and Crick Model

Two polynucleotide - Monomer of DNA are nucleotide
strands (deoxyribonucleotide)

- DNA molecule consists of two
polynucleotide strands.

- The two strands twist around each other,
forming a double helix.

- Each complete turn of the helix has 10

base pairs.
- The two strands run in opposite

directions to each other and are therefore

antiparallel.
- The two strands are held together by

hydrogen bonds between the

complementary base pairs.
- Adenine linked to Thymine by 2

hydrogen bonds. Guanine linked to
Cytosine by 3 hydrogen bonds.
- Sugar (deoxyribose) linked to phosphate
group by phosphodiester linkage to form

backbones.
- The sugar-phosphate backbones are on the

outside of the helix.
- The end of the strand with a free phosphate

group is the 5’ end because the phosphate
group is attached to the 5’ carbon of the
sugar.
- The other end of the same strand with a
free hydroxyl group is the 3’end because
the hydroxyl group is attached to the 3’
carbon of the sugar.

END OF TOPIC

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