CHAPTER 4 CHEMICAL COMPOSITION IN A CELL

CHAPTER 4
CHEMICAL
COMPOSITION IN A CELL

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4.1 WATER

Properties Of Water And Its Importance In A Cell

POLARITY OF WATER COHESIVE FORCE AND ADHESIVE FORCE OF
C1 : Inorganic compound consisting of the hydrogen WATER

and oxygen elements C1 : Water molecules are attached to each other
C2 : Polar molecules because shared electrons through a cohesive force

between oxygen and hydrogen will be attracted C2 : Water molecules are also attached to other
towards oxygen which is more electronegative surfaces through adhesive force
C3 : The polarity produces hydrogen bonds and allows
water to act as a universal solvent C3 : Both forces produce the capillary action – allow
C4 : The universal solvent properties of water allow water enter and move along narrow spaces
solutes such as glucose and electrolytes to be such as in the xylem tube
transported through the plasma membranes into
cells for biochemical reactions SPECIFIC HEAT CAPACITY OF WATER
C1 : Water has a high specific heat capacity of 4.2kJkg-1C-1
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raise the temperature of 1 kilogram of water by 1ºC
C3 : Water absorbs a lot of heat energy with a small rise in

temperature. This characteristic is very important to
maintain the body temperature of organisms

4.2 CARBOHYDRATES

 Organic compounds consisting of carbon (C), MONOSACCHARIDES
hydrogen (H) and oxygen (O) in the ratio 1:2:1
and with the chemical formula (CH2O)n  Carbohydrate monomers
 Can combine to form polymers through a condensation
 Three types of carbohydrate :
- Monosaccharides (simple sugar reaction
- Disaccharides  Taste sweet, can form crystals and dissolve in water
- Polysaccharides (complex sugar)  Examples :

i. Glucose : found in plants such as rice, wheat
and grapes

ii. Fructose : sugar found in honey and sweet fruit
iii. Galactose : found in milk
 Have a reducing power, ability to transfer hydrogen (or
electron) to other compounds
 When the monosaccharide is heated with Benedict’ solution,
the monosaccharide will reduce the blue copper (II) sulphate
to brick red precipitate of copper (I) oxide which is not
soluble in water
 This reaction known as reducing sugars

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DISACCHARIDES

 CONDENSATION PROCESS
Are formed when two simple sugar molecules (monosaccharides) combine through condensation to form a
disaccharide unit
This process involves the removal of a water molecule

condensation

GLUCOSE + GFGRLAUULACCOCTTSOOESSEEccoonnddeennssaattiioonn MALTOSE + WATER
GLUCOSE + SUCROSE + WATER
GLUCOSE + LACTOSE + WATER

 HYDROLYSIS PROCESS
Disaccharides can also be broken down to their monosaccharide
This process involves addition of one water molecule

MALTOSE + WATER hydrolysis GLUCOSE + GLUCOSE
SUCROSE + WATER GLUCOSE + FRUCTOSE
LACTOSE + WATER hydrolysis GLUCOSE + GALACTOSE
hydrolysis

 Example of Disaccharides : Sucrose (sugar cane, sweet fruit and sugar beet), maltose (grains) and
lactose (milk)
 Maltose and lactose are reducing sugars while sucrose is a non-reducing sugar
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POLYSACCHARIDES

 Are sugar polymers consisting of monosaccharide monomer
 Formed through the condensation process and involves hundreds of

monosaccharides to form long molecular chains
 Not soluble in water due to their large molecular size
 Neither taste sweet nor crystallize
 Polysaccharides can also disintegrate through hydrolysis with the help

of dilute acids, boiling and enzyme action

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IMPORTANCE OF CARBOHYDRATE IN
CELLS

 As a source of energy, for example glucose
 As food reserve, for example glycogen in animal

cells and starch in plant cells
 As a support structure, for example cellulose in

their plant cell wall

 Starch is the main storage of Cellulose forms the main
polysaccharide in plant. structure of the plant cell wall

 Starch is also found in chloroplasts  Glycogen is the main storage of
 Source : grains, potatoes and legumes polysaccharide found in muscle cells

and animal liver cells

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4.3 PROTEIN

 Complex compound composed of Carbon, Hydrogen, Oxygen and Nitrogen elements
 Most protein also contain Sulphur and phosphorus
 Foods rich in proteins include fish, meat, milk, beans and eggs
 All proteins are composed of one or more polymers known as polypeptides
 Polypeptides is made up of monomers known as amino acid
 Amino acids are linked together through the condensation process

 Dipeptides = composed of two amino acid molecules which are linked together by a peptide bone
through condensation

= one molecule of water is removed
= link more amino acids to form a polypeptide chain
= each dipeptide can be broken down into an amino acid through hydrolysis
= one molecule of water is added

Amino acid + Amino acid condensation Dipeptide + Water
Dipeptide + Water hydrolysis Amino acid + Amino acid

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4.3 PROTEIN

IMPORTANCE OF PROTEINS IN A CELL

i. Used to build new cells
ii. Repair damaged tissues
iii. Used to synthesis of enzymes, hormones, antibodies and haemoglobin
iv. Also form building blocks such as keratin in the skin, collage in bones and myosin

in muscle tissues
v. The breakdown of proteins or polypeptides by digestive enzymes gives us the

energy
vi. Polypeptides can disintegrate into amino acids, this amino acid is then again to

build the protein molecules needed by the body.

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4.4 LIPIDS

 Are naturally occurring hydrophobic compounds found in plant and animal
tissues
 Lipid is made up of carbon, hydrogen and oxygen elements but with a much
higher ratio of hydrogen atoms to oxygen atoms
 Insoluble in water but soluble in other organic solvents for example alcohol,
ether and chloroform
Types of lipid Fats
Waxes

Phospholipid Steroids

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FATS

 Fats and oils are triglycerides
 Triglycerides are a type of ester formed from the condensation of one

glycerol molecules with three molecules of fatty acids
 Triglycerides can be hydrolysed again into fatty acids and glycerol through

the reaction of hydrolysis
 Glycerols are a type of three carbon alcohol that contain three hydroxyl

groups (-OH)

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TYPES OF FATTY ACIDS
SIMILARITIES

 Both consist of carbon, hydrogen and oxygen elements
 Both contain glycerol and fatty acids
 Both contain nonpolar molecules

DIFFERENCES

SATURATED FATS UNSATURATED FATS

Fatty acids only have single bonds between carbon Fatty acids have at least one double bond between carbon

Do not form chemical bonds with additional hydrogen atoms Double bonds can still receive one or more additional hydrogen
because all bonds between carbon atoms are saturated atoms because carbon atoms are unsaturated
Exists in solid form at room temperature Exists in liquid form at room temperature

Source : butter and animal fat Source : olive and fish oil

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WAX PHOSPHOLIPID STEROID

C1 : contains one molecule of C1 : major component of plasma membranes C1 : are lipids that do not contain fatty
alcohol that combines with C2 : made up of one molecule of glycerol acids
another molecule of fatty that combines
acid E : cholesterol, testosterone, estrogen
with two molecules of fatty acid and and progesterone
C2 : Waterproof one group of

phosphate

IMPORTANCE OF LIPIDS IN CELLS
FATS :
 As a reserved energy for animals
 As a liner to protect internal organs
 Act as a heat insulator for animal
WAXES:
 Component in cuticles that cover the epidermis of leaves and sebum secreted by our skin
GLYCOLIPID
 To ensure the stability of the plasma membrane
 Help in the cell identification process
CHOLESTEROL
 Important in steroid hormone synthesis
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4.5 NUCLEIC ACIDS

 One or two polymer chains comprising of nucleotide monomers
 Formed from the elements of carbon, hydrogen, oxygen, nitrogen and phosphorus
 Each nucleotide consists of a pentose sugar (5-carbon sugar), a nitrogenous base and

phosphate group that are combined together through the condensation process

Nitrogenous base: Types of pentose sugar Types of Nucleic Acids:
i. Adenine (A) : i. Deoxyribonucleic acid (DNA) :
ii. Guanine (G)
iii. Cytosine (C) i. Ribose contains deoxyribose sugar
iv. Thymine (T) ii. Deoxyribose ii. Ribonucleic acid (RNA) : contains
v. Uracil (U)
ribose sugar

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DEOXYRIBONUCLEIC ACID (DNA)

 DNA consists of two polynucleotide chains
that are intertwined in opposite directions
and form the double helix

 The nitrogenous base groups on both
polynucleotide chains are matched and
bound together by hydrogen bonds

 The nitrogenous bases for DNA are adenine
(A), guanine(G), thymine(T) and cytosine
(C)

 Adenine = Thymine
 Guanine = Cytosine

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ROIBnOeNorUtCwLoEIpColyAmCeIDr c(hRaNinAs )comprising of nucleotide monomers

RNFAoirsma esidnglefproolymnucltehoteideechleaimn ewnhitcsh of carbon, hydrogen, oxygen, nitrogen and
TiasdheEpsenhhanionocirtetshr,eoprggnhuecauononomrciunulpseeas,robeactdsyidtetosoesfiDnocNeroAaRnnNsdAiusartrasecilof a pentose sugar (5-carbon sugar), a nitrogenous
 Thbymaisnee in aDnNdA is prehpolascpedhabyteuracgilrionup that are combined together through the
 RTNhcAeotnhdreeenmsaaitniotynpepsroofcReNsAs:

i. Messenger RNA (mRNA)
ii. Ribosomal RNA (rRNA)
iii. Transfer RNA (tRNA)
 These three RNAs are involved in the

protein synthesis process

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 As a carrier of hereditary information and a determinant of IMPORTANCE OF NUCLEIC
characteristics in living organisms ACIDS IN A CELL

 DNA contains genetic codes carried by nitrogenous bases (A, G, C PREPARED BY CIKGU HUSRITA MRSM TRANSKRIAN
and T) for the synthesis of polypeptides which form proteins

 The genetic code is written as a series of three bases that
determine the sequence of amino acids in proteins to be
synthesized

 Example :
AUG codon (base sequence : Adenine, Uracil and Guanine) on
mRNA is the code for methionine
amino acid

 The three-base sequence in DNA is transcribed into mRNA codons
which are then translated into the amino acid sequence to form a
single polypeptide chain.

 This means that the sequence of nucleotides in DNA determines
the amino acid sequence in the polypeptide chain that builds the
corresponding protein

 Chromosomes are formed from FORMATION OF CHROMOSOMES FROM DNA
DNA polynucleotide chains that AND PROTEINS
are wound around a protein
called histone

 Histones do not carry genetic
information

 DNA molecules combine with
histone proteins to form
nucleosomes

 Nucleosomes are intertwined to
form the chromosome structure

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