Chemical components of living organisms
Dec 23, 2015
Learning objectives To identify the basic chemical components
of living organisms. To define roles of carbohydrates, proteins
and lipids in terms of energy storage and structural components.
To describe formation of carbohydrate, proteins and lipid from basic units.
To identify deoxyribonucleic acid (DNA) and ribonucleic acid(RNA) with their bases.
To differentiate between DNA and RNA.
The basic chemical components of living organisms
Carbohydrate Proteins Lipids Nucleic acids Water Mineral salts
Carbohydrate Carbon + Hydrogen + Oxygen General formula: Cx(H2O)y. Types of carbohydrates: ~ Monosaccharides ~ Disaccharides ~ Polysaccharides
Galactose & ribose Galactose ~ Found in milk Ribose ~ Constituent of ribonucleic acid(RNA)
and deoxyribonucleic acid (DNA)
Disaccharide 2 monosaccharides joining together b
y glycosidic bond undergoing a condensation reaction.
Disaccharide can be split into its constituent monosaccharides by hydrolysis.
Sweet, soluble and crystalline Maltose, sucrose, lactose
Maltose Glucose + Glucose Maltose Glucose + Glucose +…… starch It is hydrolysed back to 2 glucose
molecules by maltase.
Sucrose Glucose + fructose sucrose It is also called cane-sugar. It is hydrolysed back to glucose
and fructose by invertase.
Lactose Glucose + galactose lactose It is hydrolysed back to glucose and g
alactose by lactase. Lacking lactase in the body lactose
intolerance
Polysaccharides Complex sugar Compounds of a large number of mon
osaccharides units Insoluble Converted into monosaccharides upo
n hydrolysis As food and energy store
Polysaccharide Starch ~ major food reserve stored
in plants but absent in animal. Glycogen ~ animal starch, stored
in liver & muscles. Cellulose ~ constitute of plant cell
wall, insoluble in water & dissolves in concentrated sulphuric acids.
Tests for carbohydrates
Reducing sugar: Benedict’s test Clinistix paper testNon-reducing sugar: Acid hydrolysis Enzyme actionStarch Iodine test
Lipids Carbon + Hydrogen + Oxygen Insoluble in water but dissolve in
organic solvents. Fat: semi-solid at room temperature Oils: liquid at room temperature Types of lipids: triglycerides,
phospholipids
Function of lipids Food reserve Structural
materials Insulation Water-proof layer Transport
medium
Metabolic regulators
Energy source Protection Others
Proteins Polymer of amino acids Insoluble in water Carbon + Hydrogen + Oxygen + nitrog
en +/- sulphur & phosphorus Basic units: amino acid
Proteins Amino acid + Amino acid
Dipeptide Dipeptide + Dipeptide
Polypeptide The reaction “” is condensation. 4 types of bonding: disulphide
bond, ionic bond, hydrogen bond & hydrophobic interaction.
Denaturation Denaturation ~ loss of specific three dimensional
conformation of a protein molecule;
~ but the amino acids sequence remains unaffected;
~ loss of biological activities
Factors causing denaturation Heat or radiation Extreme pH Inorganic chemicals Organic chemicals Mechanical force Strong hydrogen bond former
Types of proteins Fibrous protein ~ regular repetitive
sequences of amino acid;
~ parallel chain; ~ insoluble in water ~ e.g. collagen of
tendons & ligaments
Globular protein ~ irregular
sequences of amino acid;
~ spherical & globular shapes chains;
~ e.g. enzymes, antibodies & hormones.
Functions of proteins Structural
materials Biocatalyst Metabolic
regulators Transportation Protection
Muscle contraction
Storage Toxins Respiratory
substrate
Nuleotides Phosphoric acid + Pentose sugar + Or
ganic base The three components are combined
by condensation reaction
Types of nucleotides Mononucleotides: only one nucleotid
e unit, e.g. ATP Dinucleotides: 2 nucleotides e.g. NAD Polynucleotides: repeated condensati
on of nucleotides e.g. RNA & DNA
DNA vs RNADNA
Single strand Base: A, T, C & G Sugar: Deoxyribose Size: long & large Stability: alkali-stabl
e Function: carry gene
tic information Occurrence: in nucle
us
RNA Single strand Base: A, U, C & G Sugar: ribose Size: short & small Stability: stable Function: protein
synthesis, carry genetic information from DNA
Occurrence: throughout cell
Water Comprise 65-95% of living cells. High specific heat. Strong hydrogen bond. Universal solvent. High tensile strength and high
viscosity. High surface tension
Importance of water to life Component of protoplasm. Universal solvent. Participating in metabolic process. Cell turgidity. Surface film. Temperature stability. Translocation medium.