BIOLOGY SCORE| SB015
CHAPTER 1: MOLECULES OF LIFE
SUBTOPIC: 1.1
WATER LEARNING
OUTCOME:
a) State the structure and properties of water molecules
b) Relate the properties of water and its importance: universal/ versatile solvent, high specific heat
capacity, high latent heat of vaporization, cohesion of water molecules and maximum density at 4◦C.
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
• Water has simple molecular formula. It composed of one
Water molecules oxygen atom and two hydrogen atoms.
• A hydrogen atom combined with the oxygen atom by
sharing ofelectrons.
• 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 moreelectronegative compared to hydrogen.
• The angle between the two covalent bonds is 104.5°
• Oppositely charged regions in neighboring water molecules are
attract to each other by hydrogen bond
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Properties of • Universal solvent due to its polarity / polar molecules
water and its • The unequal sharing of electrons and water V-like shape
importance: make it a polar molecule
• When in contact with H2O, ions (e.g.: salts) and polar (e.g.:
sugar) groups are surrounded by H2O molecules
• Water separate the ions and molecules from each other.
• Example: Dissolving sodium chloride in water.
o The negative ends of water molecules are attracted to
sodium ion
o 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.
• 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 tospeed up its molecules.
• As a result, organism can maintain stable body temperature.
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• 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.
• Cohesion of water molecules
• 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 (e.g., Water strider) to
walk on pond without breaking the
surface.
• 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
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f) 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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SUBTOPIC: 1.2 CARBOHYDRATE
LEARNING OUTCOME:
a) State the classes of carbohydrates such as monosaccharide, disaccharides and
polysaccharides.
b) Illustrate the formation and breakdown of maltose
c) Compare the structures and functions of starch, glycogen and cellulose.
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
▪ Organic compounds containing carbon, hydrogen and oxygen
Carbohydrates with the ratio of 1:2:1
▪ Empirical formula (CH2O) n
Three classes of carbohydrates:
Classes of Classes Example
carbohydrates Monosaccharides Glucose, fructose and galactose
Disaccharides Maltose, sucrose and lactose
Polysaccharides Starch, glycogen and cellulose
▪Sweet tasting
Characteristics of ▪Primary source of energy
monosaccharides ▪ Readily soluble in water
▪Reducing sugar – benedict test
▪Can be crystallized
▪Have a carbonyl group(CO)and multiple hydroxyl groups(OH)
Classification of Depending on the location of the carbonyl group, sugar is
monosaccharides grouped into Aldoses or Ketoses
Aldoses Ketoses
Carbonyl group is located Carbonyl group is located at a
at the terminal carbon in carbon that is not at the end of
the chain/ carbon skeleton the chain/carbonyl
group is in the middle of
the carbon skeleton.
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Interconvertibl
eforms of α – glucose β –glucose
glucose -OH group of the first carbon -OH group of the first
atom is located below the carbon atom is located
plane of the ring 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.
Polysaccharide ▪ Macromolecules, polymers of monosaccharides which joined
s by glycosidic linkage.
▪ Example of polysaccharides: Starch, glycogen and cellulose
Formation ▪ Disaccharides are formed by the condensation reactions of
and two simple sugar molecules.
breakdown of ▪ Two OH groups, one from each sugar molecule, combine
maltose. together to release water and form an oxygen bridge between
them.
Formation of
Maltose.
Breakdown of
Maltose.
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Comparison ▪ A granular, tasteless, insoluble in cold water and organic
between the molecule that is produced by all green plants
structures and ▪ The basic chemical formula of the starch molecule is
functions: (C6H10O5)n. Starch is polysaccharide comprising of glucose
monomers joined by α -1,4 glycosidic bonds linkages.
▪ The simplest form of starch is the
Starch 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
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.
α-1,6 glycosidic bonds
α-1,4 glycosidic bonds
▪ Function as major storage in animals
▪ Insoluble in water
▪ Structure similar to amylopectin but larger and with
Glycogen moreextensively branched
▪ The linear chain of α glucose is held together by α -1,4
glycosidic bond and branches are held by α -1,6 glycosidic
bonds.
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Cellulose ▪ Structural polysaccharides in plant cell walls.
▪ Composed of long unbranched chains of β- glucose subunits
linked by β -1,4 glycosidic bond.
▪ Many hydrogen bonds are formed between hydroxyl groups
on parallel chains (between carbon atoms 3 and 6).
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SUBTOPIC: 1.3 LIPIDS
LEARNING OUTCOME:
a) State the types of lipids:
i. triglycerides (fats and oil)
ii. phospholipids
iii. steroids.
b) Describe the structure of fatty acids and glycerol.
c) Explain the formation and breakdown of triglycerides.
MAIN IDEAS EXPLANATION NOTES
/KEY POINT
▪ Lipids are organic compounds.
Lipid ▪ Consist of carbon, hydrogen and oxygen.
▪ Proportion of oxygen is lower than in carbohydrates.
▪ General formula: CnH2nO.
▪ Can store large amount of energy.
▪ The ratio of energy storing C-H bonds in fats is more than
twice thatcarbohydrates / more C and H.
▪ Insoluble in water but soluble in organic solvent.
▪ Three types of lipids:
▪ Triglyceride consist of 1 molecule of glycerol joined to
Triglycerides 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.
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Saturated Fat Unsaturated Fat
Contain saturated fatty acids Contain unsaturated fatty
acids
Solid state at room Liquid state at room
temperature temperature
Found in animals Can be found in plant and fish
No double bond between Has one or more double
carbon atoms bonds between carbon atoms
which reduces the numberof
bonded hydrogen atoms
▪ Similar to a fat molecule but has only two fatty acids attached
Phospholipids to glycerolrather 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.
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▪ Many hormones, as well as cholesterol, are steroids, which are
Steroids lipids characterized by a carbon skeleton.
▪ Have a basic four- ring hydrocarbon structure with
different functional side chains.
Formation and ▪ Triglycerides are formed by combining one glycerol with
breakdown of three fatty acid molecules through the process of
Triglycerides condensation.
▪ Alcohols have a hydroxyl (HO–) group.
▪ Organic acids have a carboxyl (–COOH) group.
▪ Alcohols and organic acids join to form esters.
condensation
hydrolysis
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SUBTOPIC: 1.4 PROTEINS
LEARNING OUTCOME:
a) Describe the basic structure of amino acids.
b) State how amino acids are grouped
c) Describe primary (10), secondary (20), tertiary (30) and quaternary (40) levels of proteins and the
types of bonds involved.
d) Describe the effect of pH and temperature on the structure of protein.
e) Explain the formation and breakdown of dipeptide.
f) Classify proteins according to structure and composition.
MAIN IDEAS EXPLANATION NOTES
/ KEY
POINT
Protein ▪ Organic compounds containing carbon, hydrogen, oxygen
and nitrogen.
▪ Are polymers with repeated units of monomers (amino acids)
Protein ▪ Amino acids joined together by peptide bond formed a
monome polypeptide chain or protein.
r ▪ 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):
o Nonpolar amino acid
o Polar amino acid
o Acidic amino acid
o Basic amino acid
Glutamic acid Lysine
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Levels of proteins
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Effects of pH and Factor Explain Examples
temperature Temperature ▪ Heat increases the E.g.: Fried
kinetic egg white
▪ 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.
pH ▪ Extreme pH can cause E.g.:
protein to denature. Enzymes
▪ Change the charges are affected
of acidic and basic by changes in
functional groups of pH
proteins.
▪ Those functional groups
will lose or gain a
proton.
▪ Break hydrogen bonds
between acidic and basic
R groups and disrupt
ionic bonds.
Denaturation: High temperature or various chemical treatments
will denature a protein, causing it to lose its shape and hence
ability to function.
Renaturation:
Denatured proteins remain dissolved, it may renature when the
chemical and physical aspects of its environment are restored to
normal
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Formation and ▪ Amino acids are joined together by a condensation /
breakdown of dehydration reaction.
dipeptide
▪ Breakdown of dipeptide during hydrolysis (water molecules
adds) across the peptide bond forming amino acids.
Protein Fibrous Protein Globular Protein
classificatio
▪ Long polypeptide Compact polypeptide
n according
Structure chains chain, tightly folded,
to their
soluble in water to
structure and ▪ Insoluble in
form colloidal
composition water, stable and
suspension and
. tough
unstable structure
Examples ▪ Collagen ▪ Enzyme
▪ α- keratin ▪ antibody,
▪ elastin ▪ hemoglobin
Composition Simple Protein Conjugated Protein
Protein composed only Protein contains with
of amino acid prosthetic groups
Example ▪ Globulin ▪ Hemoglobin
▪ Histone ▪ Glycoprotein
▪ Lipoprotein
▪ Phosphoprotein
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SUBTOPIC: 1.5 DNA and RNA MOLECULES
LEARNING OUTCOME:
a) State the structure of nucleotide as the basic components of nucleic acid (deoxyribonucleic acid,
DNA and RNA).
b) Illustrate the structure of DNA based on the Watson and Crick Model.
c) Explain the structure of DNA and RNA
d) State the types of RNA.
MAIN IDEAS EXPLANATION NOTES
/ KEY POINT
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
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▪ The portion of a nucleotide WITHOUT the phosphate
group is called nucleoside
▪ Nitrogenous bases are divided into two families:
▪ Purines
▪ Pyrimidines
▪ Nitrogenous bases in nucleic acids:
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Ring structure Base Found in
Purines
▪ Two carbon nitrogen rings Adenine (A) DNA/
▪ Four nitrogen atoms Guanine (G) RNA
Pyrimidines
▪ Single carbon-nitrogen ring Cytosine (C) DNA/RNA
▪ 2 nitrogen atoms Thymine (T) DNA
Uracil (U) RNA
▪ Phosphodiester bond between phosphate group at C5 of one
pentose sugar and hydroxyl group (OH) at C3 of the next
pentose through condensation process.
▪ Sugar and phosphate group of adjacent nucleotides are linked
together by phosphodiester bond forming a sugar phosphate
backbone of a polynucleotide strand.
Structure of ▪ James Watson and Francis Crick proposed the double helix
DNA based on model of DNA in 1953.
the Watson and
Crick Model
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▪ 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:
o Adenine always pairs with thymine
o Guanine always pairs with cytosine
o 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:
o Main genetic material in virus
o Involve in protein synthesis
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▪ 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:
Differences
between DNA DNA RNA
and RNA
Consist of two Consist of single
polynucleotide chains // polynucleotidechain //
double stranded single stranded
Pentose sugar is deoxyribose Pentose sugar is ribose.
Organic bases: A, T, C, G Organic bases: A, U, C, G
* Base Thymine (T) * Base Uracil (U)
Manufactured and found in Manufactured in nucleus
nucleus but found throughout the
cell
Chemically very stable Chemically much less stable
Permanent Temporary existing
Only one basic form 3 basic forms: mRNA,
rRNAand tRNA
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