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SB015Chapter 1: Molecules Of LifeBioScore
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BIOLOGY SCORE
CHAPTER 1 : MOLECULES OF LIFE SUBTOPIC : 1.1 Water
LEARNING OUTCOME:
i. Explain the structure of water molecule.
ii. Describe the properties of water and its importance:
Universal solvent
Low viscosity
High specific heat capacity
• High latent heat of vaporization
• High surface tension
• Maximum density at 4°C
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
Water molecules
▪ Water has simple molecular formula. It composed of one oxygen atom
and two hydrogen atoms.
▪ A hydrogen atom combined with the oxygen atom by sharing of
electrons.
▪ Each hydrogen atom is covalently bonded to the oxygen via a shared
pair of electrons.
▪ Oxygen also has two unshared pairs of electrons. Thus, oxygen is more
electronegative compared to hydrogen.
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▪ The angle between the two covalent bonds is 104.5°
▪ Oppositely charged regions in neighboring water molecules are attracted
to each other by hydrogen bond_
Properties of
water and its
importance:
- universal
solvent due to its
polarity / polar
molecules
▪ The unequal sharing of electrons and water V-like shape make it a polar
molecule.
▪ When in contact with H2O, ions (eg :salts) and polar (eg: sugar) groups
are surrounded by H2O molecules
▪ Water separate the ions and molecules from each other
Example: Dissolving sodium chloride in water.
▪ The negative ends of water molecules are attracted to sodium ion
▪ The positive ends of the water molecules are attracted to chloride ions.
▪ This causes water molecules surround the individual sodium and
chloride ion and form hydration shell.
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Properties of
water and its
importance:
- low viscosity
▪ water has low viscosity so is a suitable medium for transportation in
living organisms
▪ in animals, low viscosity of water enable the blood plasma and lymph
to flow easily in the circulatory system.
▪ in plants, water in the xylem and phloem can move easily
Properties of
water and its
importance:
- high specific
heat capacity
▪ Water has high specific heat capacity so large amount of energy is
needed to break down the hydrogen bonds among water molecules
before the water molecules can begin to move about more freely and
therefore, causing an increase in temperature.
▪ Water resists changes in temperature and a lot of energy needed to
speed up its molecules.
▪ As a result, organism can maintain stable body temperature
Properties of
water and its
importance:
- High latent
heat of
vaporization
▪ Water has high latent heat of vaporization because hydrogen bonding
between molecules is difficult to be separated and vaporized
▪ When water is heated, it evaporates more rapidly than when it is
cooled. As a result, water,stabilizes temperature in lakes and ponds
provides a mechanism that prevents terrestrial organism from
overheating.
▪ Evaporation of sweat from human skin dissipates body heat and helps
prevent overheating on hot day or when excess heat is generated by
strenuous activity
Properties of
water and its
importance:
-high surface
tension
▪ Water has high surface tension due to cohesion. Cohesion is the linking
together of like water molecules by hydrogen bonds. High surface
tension allows insects (eg. water strider) to walk on pond without
breaking the surface
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▪ Adhesion is the clinging of water molecules to another substance.
▪ Cohesion and adhesion contribute to the transport of water and
dissolved nutrients against gravity in plants
Properties of
water and its
importance:
-Maximum
density at 4°C
▪ Water is less dense as a solid (ice) than as a liquid (water). Ice floats on
liquid water. Water molecules expand when solidify. Floating ice
insulate the water below preventing it from freezing. It allows marine
life to exist under the frozen surface .
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BIOLOGY SCORE
CHAPTER 1 : MOLECULES OF LIFE Subtopic : 1.2 Carbohydrates
Learning Outcome :
i. State the classes of carbohydrate
ii. Illustrate the formation and breakdown of maltose
iii. Compare the structures and functions of starch, glycogen and cellulose.
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
Carbohydrates
▪ Organic compounds containing carbon, hydrogen and oxygen with
the ratio of 1:2:1 ▪ Empirical formula (CH2O)n
Classes of
carbohydrates
Three classes of carbohydrates :
Classes Example
Monosaccharides Glucose, fructose and
galactose
Disaccharides Maltose, sucrose and
lactose
Polysaccharides Starch, glycogen and
cellulose
Characteristics
of
monosaccharides
▪ Sweet tasting ▪ Primary source of energy ▪ Readily soluble in water ▪ Reducing sugar – benedict test ▪ Can be crystallized ▪ Have a carbonyl group (CO) and multiple hydroxyl groups (-OH)
Classification of
monosaccharides
Depending on the location of the carbonyl group, sugar are grouped
into Aldoses or Ketoses
Aldoses Ketoses
Carbonyl group is located
at the terminal carbon in
the chain/ carbon skeleton
Carbonyl group is located
at a carbon that is not at the
end of the chain/carbonyl
group is in the middle of the
carbon skeleton.
Example:
ribose, glucose , galactose
and glyceraldehyde
dihydroxyacetone, ribulose
and fructose
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Interconvertible
forms of glucose
α – glucose β –glucose
-OH group of the first
carbon atom is located
below the plane of the ring
-OH group of the first
carbon atom is located
above the plane of the ring
Disaccharides ▪ Consists of two monosaccharides joined by a glycosidic bond which
formed by a condensation reaction. ▪ Example of disaccharides :Sucrose, maltose and lactose ▪ Characteristics of disaccharides: Same as monosaccharides.
Polysaccharides ▪ Macromolecules, polymers of monosaccharides which joined by
glycosidic linkage.
Formation and
breakdown of
maltose.
▪ Disaccharides are formed by the condensation reactions of two
simple sugar molecules. ▪ Two OH groups, one from each sugar molecule, combine together
to release water and form an oxygen bridge between them .
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Comparison
between the
structures and
functions:
Starch
▪ A granular, tasteless, insoluble in cold water and organic molecule
that is produced by all green plants ▪ The basic chemical formula of the starch molecule is (C6H10O5)n.
Starch is polysaccharide comprising of glucose monomers joined
by α -1,4 glycosidic bonds linkages. ▪ The simplest form of starch is the
o Amylose - linear polymer; o Amylopectin - the branched form.
Amylose
▪ A linear unbranched polymer: straight chain ▪ Amylose chain coils into helix:
o held by hydrogen bonds formed between hydroxyl groups ▪ Glucose units joined by α -1,4 glycosidic bonds
Amylopectin
▪ a branched polymer ▪ linear chains held together by α -1,4 glycosidic bonds ▪ short branches: intervals of approximately 25- 30 monomers where
α -1,6 glycosidic bonds occur
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Glycogen
▪ Function as major storage in animals ▪ Insoluble in water ▪ Structure similar to amylopectin but larger and with more
extensively branched ▪ The linear chain of α glucose are held together by α -1,4 glycosidic
bond and branches are held by α -1,6 glycosidic bonds
Cellulose
▪ Structural polysaccharides in plant cell walls. ▪ Composed of long unbranched chains of β- glucose subunits linked
by β -1,4 glycosidic bond
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BIOLOGY SCORE
CHAPTER 1 : MOLECULES OF LIFE Subtopic : 1.3Lipids
Learning Outcome :
i. State the types of lipid: triglycerides (fat and oil), phospholipids and steroids.
ii. Describe the structure of fatty acids and glycerols.
iii. Explain the formation and breakdown of triglycerides.
MAIN
IDEAS /KEY
POINT
EXPLANATION NOTES
Lipid
▪ Lipids are organic compounds.
▪ Consist of carbon, hydrogen and oxygen.
▪ Proportion of oxygen is lower than in carbohydrates.
▪ General formula : CnH2nO2
▪ Can store large amount of energy.
▪ The ratio of energy storing C-H bonds in fats is more than twice that
carbohydrates / more C and H
▪ Insoluble in water but soluble in organic solvent
▪ Three types of lipids
● Triglycerides
● Phospholipids
● Steroids
Triglycerides
▪ Triglyceride consist of 1 molecule of glycerol joined to three molecules of
fatty acids by ester bonds. ▪ Glycerol is a three-carbon alcohol that contains three hydroxyl group (-OH) ▪ A fatty acid is a long, unbranched hydrocarbon chain with carboxyl group (-
COOH) at one end. ▪ Form fats and oils mainly for energy storage
Ester bond
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Saturated Fat
Unsaturated Fat
Contain saturated fatty acids Contain unsaturated fatty acids
Solid state at room temperature Liquid state at room temperature
Found in animals
Can be found in plant and fish
No double bond between carbon
atoms
Has one or more double bonds between
carbon atoms which reduces the number
of bonded hydrogen atoms
Phospholipids
▪ Similar to a fat molecule but has only two fatty acids attached to glycerol
rather than three.
▪ The third hydroxyl group of glycerol is joined to a phosphate group, which
has a negative charge.
▪ Essential for cells because they make up the cell membrane
Steroids
▪ Many hormones , as well as cholesterol, are steroids, which are lipids
characterized by a carbon skeleton.
▪ Have a basic four- ring hydrocarbon structure with different functional side
chains.
Formation
and
breakdown
of
Triglycerides
▪ Triglycerides are formed by combining one glycerol with three fatty acid
molecules through the process of condensation . Alcohols have a hydroxyl
(HO–) group. Organic acids have a carboxyl (–COOH) group.
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▪ Alcohols and organic acids join to form esters.
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BIOLOGY SCORE
CHAPTER 1 : MOLECULES OF LIFE
Subtopic : 1.4 Proteins
Learning Outcome :
i. Describe the basic structure of amino acids.
ii. State how amino acids are grouped
iii. Describe primary, secondary, tertiary and quaternary levels of proteins and the types of bonds
involved.
iv. Describe the effects of pH and temperature on the structure of protein.
v. Explain the formation and breakdown of dipeptide.
vi. Classify proteins according to their structure and composition.
MAIN IDEAS /
KEY POINT
EXPLANATION NOTES
Protein ● Organic compounds containing carbon, hydrogen , oxygen
and nitrogen.
● Are polymers with repeated units of monomers ( amino acids)
Protein
monomer
● Amino acids joined together by peptide bond formed a
polypeptide chain or protein.
● Molecules contains amino group, a carboxyl group, a
hydrogen atom and a side chain (specific to each amino acid).
● Amino acids are grouped according to the properties of their
side chain (R group) :
a) Nonpolar amino acid
b) Polar amino acid
c) Acidic amino acid
d) Basic amino acid
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Levels of
proteins
● There are 4 levels of proteins and types of bonds involved :
Levels of
proteins
Bond(s) E.g :
Primary (1ͦ) Peptide Insulin
Secondary (2)ͦ Hydrogen Keratin, spider
cobweb, silk
Tertiary (3ͦ)
(consist of
single
polypeptide
chain)
Hydrogen bond, Ionic
bond, disulphide bridge,
hydrophobic and van de
Waals interaction
Myoglobin,
enzyme
Quaternary (4)ͦ
(consist of more
than one
polypeptide
chain)
Hydrogen bond, Ionic
bond, disulphide bridge,
hydrophobic and van de
Waals interaction
Haemoglobin
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Effects of pH
and temperature
Explain Examples
Temperature • Heat increases the kinetic
energy of the protein chain.
• Excessive motion can
break relatively weak
hydrogen bonds, electrostatic
interactions (ionic bond) and
hydrophobic interactions.
• Protein chain is free to
rearrange after disrupting.
• E.g : Fried
egg white
pH • Extreme pH can cause
protein to denature.
• Change the charges of
acidic and basic functional
groups of proteins.
• Those functional groups will
lose or gain a proton.
• Break hydrogen bonds
between acidic and basic R
groups and disrupt ionic
bonds.
E.g: Enzymes
are affected by
changes in pH.
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Denature/
Renature
Denaturation :
High temperature or various
chemical treatments will
denature a protein, causing it
to loose its shape and hence
ability to function.
Renaturation:
Denatured proteins remains
dissolved, it may renature
when the chemical and
physical aspects of its
environment are restore to
normal.
Formation and
breakdown of
dipeptide
● Amino acids are joined together by a condensation /
dehydration reaction.
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● Breakdown of dipeptide during hydrolysis (water molecules
adds) across the peptide bond forming amino acids.
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Protein
classification
according to
their structure
and
composition.
● Classes of proteins based on the structure:
Class Fibrous Globular
Characteristic
s
Long
polypeptide
chains,
Insoluble in
water, stable
and tough
Compact
polypeptide
chain, tightly
folded, soluble in
water to form
colloidal
suspension and
unstable structure
Examples Collagen, α-
keratin ,elastin,
Enzyme,
antibody,
haemoglobin
● Classification of protein based on composition.
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BIOLOGY SCORE
CHAPTER 1 : MOLECULES OF LIFE
SUBTOPIC : 1.5 : DNA and RNA molecules
LEARNING OUTCOME:
i. State the structure of nucleotide as the basic components of nucleic acid (DNA and RNA).
ii. Illustrate the structure of DNA based on the Watson and Crick Model.
iii. State the types of RNA.
iv. Compare DNA and RNA.
MAIN IDEAS /
KEY POINT
EXPLANATION NOTES
Nucleic acids
● Macromolecules / polymers called polynucleotide.
● TWO types of nucleic acids : DNA and RNA
● Monomer of nucleic acids is nucleotide that made up of :
a) pentose sugar
b) Phosphate group
c) Nitrogenous bases
Components of nucleotide
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● The portion of a nucleotide WITHOUT the phosphate group is
called nucleoside
● Nitrogenous bases are divided into two families :
a) Purines
b) Pyrimidines
● Nitrogenous bases in nucleic acids :
Ring structure Base Symbol Found in
Purines
( double)
Adenine
Guanine
A
G
DNA/RNA
DNA/RNA
Pyrimidines
( single)
Cytosine
Thymine
Uracil
C
T
U
DNA/RNA
DNA
RNA
● Phosphodiester bond between phosphate group at C5 of one
pentose sugar and hydroxyl group (OH) at C3 of the next
pemtose through condensation process.
● Breakdown : hydrolysis
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● Sugar and phosphate group of adjacent nucleotides are linked
together by phosphodiester bond forming a sugar phosphate
backbone of a polynucleotide strand.
Structure of
DNA based on
the Watson and
Crick Model
● James Watson and Francis Crick proposed the double helix model
of DNA in 1953.
● DNA consist of two polynucleotide strands that coiled in a spiral
(anti parallel) to form a double helix structure.
● One strand runs 5’ to 3’ ends while the other strand runs from 3’
and 5’ ends
● Each strand must be complementary to each other
● Complementary base pairing:
● Adenine always pair with thymine
● Guanine always pair with cytosine
● Amount of A = T, amount of G = C
● Held together (base pairs) by hydrogen bond.
● A and T : Two hydrogen bonds
● G and C : Three hydrogen bonds
● The type of pentose sugar is called deoxyribose .
RNA
● RNA structure is a single stranded polymer of nucleotide.
● Functions of RNA:
a) Main genetic material in virus
b) Involve in protein synthesis
● If pairing of base occur, A will pair with U instead of T.
● The type of pentose sugar is ribose.
● 3 basic forms of RNA:
✔ Messenger RNA (mRNA)
✔ Transfer RNA (tRNA)
✔ Ribosomal RNA (rRNA)
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Differences
between
DNA and RNA
DNA RNA
Consist of two polynucleotide chains //
double stranded
Consist of single polynucleotide
chain // single stranded
Pentose sugar is deoxyribose Pentose sugar is ribose.
Organic bases: A, T, C, G
* Base Thymine (T)
Organic bases: A, U, C, G
* Base Uracil (U)
Manufactured and found in nucleus Manufactured in nucleus but
found throughout the cell
Chemically very stable Chemically much less stable
Permanent Temporary existing
Only one basic form 3 basic forms : mRNA, rRNA
and tRNA
END OF CHAPTER 1 : MOLECULES OF LIFE