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BIOLOGICAL MOLECULES (IGCSE)

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BIOLOGICAL MOLECULES
INTRODUCTION
 Everything in the physical universe is matter
 There are two main types of matter:
 Living things/matter and
 Non-living matter
BUILDING BLOCKS OF MATTER
 Matter is made up of three main types of building blocks:
 Atoms
 Ions
 molecules
BIOLOGICAL MOLECULES
 They are molecules that make up living things
 They form the building blocks of living things
WHAT ARE BIOLOGICAL MOLECULES MADE OF?
 They are made of atoms of the same element or different elements
ORGANISATION OF ORGANISMS
ELEMENTS THAT MAKE UP BIOLOGICAL MOLECULES
 The main elements that make up the molecules of living things include:
 Carbon
 Hydrogen
 Oxygen
 nitrogen
 The four main elements combine to form organic substances that make up living
organisms
ORGANIC SUBSTANCE
 It is one whose molecules contain carbon and hydrogen
TYPES OF ORGANIC SUBSTANCES
 Organic substances may be:
 Monomers or
 polymers
MONOMERS
 They are small molecules that are joined to make large molecules (polymers) by
chemical reactions
POLYMERS
 They are very large molecules formed by joining two or more small molecules
(monomers)
NOTE
 Thus, large molecules are made from smaller molecules
TYPES OF BIOLOGICAL MOLECULES FOUND IN LIVING ORGANISMS
 Biological molecules found in living organisms include:
 Carbohydrates
 Proteins
 Fats and oils/lipids
 Nucleic acids
 Vitamins
 water
CARBOHYDRATES
 They contain carbon, hydrogen and oxygen only
 They have the general formula Cx(H2O)y where x and y are whole numbers
TYPES OF CARBOHYDRATES
 There are three main types of carbohydrates, namely:
 Monosaccharides
 Disaccharides
 polysaccharides
NOTE
 “Saccharide” means “sugar” or “sweet substance”
MONOSACCHARIDES
 They are also known as simple sugars
 They are the simplest carbohydrates
 They are the monomers that can be joined to form all the other types of carbohydrates
 They are sweet tasting
 They readily dissolve in water
EXAMPLES OF MONOSACCHARIDES
 Glucose
 Fructose
 Galactose
 Ribose and deoxyribose
DISACCHARIDES
 They are formed when two monosac- charides are joined together
 They contain two carbon rings
 They are also soluble in water
 They have a sweet taste
POLYSACCHARIDES
 They are formed when many glucose or monosaccharide molecules are joined together
 They are large molecules containing a large number of monosaccharide molecules in a
long chain
 They are not soluble in water
 They do not have a sweet taste
TEST FOR CARBOHYDRATES
BENEDICT’S SOLUTION TEST FOR REDUCING SUGARS
NOTE
 Reducing sugars include glucose, fructose, galactose, maltose and galactose
IODINE SOLUTION TEST FOR STARCH
USES OF CARBOHYDRATES IN LIVING ORGANISMS
 Glucose is broken down in respiration by cells to release energy
 They are used for the storage of energy for cells
 Cellulose is used to make plant cell walls very strong which helps to maintain the
shape of the cell
NOTE
 Plants store carbohydrates as STARCH
 Animals store carbohydrates as GLYCOGEN
 These can easily be changed back to glucose and used for respiration
FATS AND OILS
 Fats and oils are also known as lipids
 They also contain the elements, carbon, hydrogen and oxygen only
 They are made of the monomers:
 Glycerol
 Fatty acids
 One glycerol and three fatty acids are joined to form a lipid molecule
 Fats are not soluble in water
 Fats are solid and oils are liquid
TEST FOR FATS AND OILS (LIPIDS)
THE ETHANOL EMULSION TEST FOR FATS
USES OF FATS AND OILS/LIPIDS IN LIVING ORGANISMS
 They can be respired by cells to release energy, producing twice as much energy as
carbohydrates
 They are used for the storage of energy for cells
 The fat store below the skin of humans act as an insulator against heat loss
 Lipids form part of the cell membrane and the internal membranes of the cell such as
the nuclear membrane
NOTE
 Fat is stored in specialized cells under the skin called adipose cells
 A layer of adipose cells under the skin forms the adipose tissue
PROTEINS
 They contain the elements carbon, hydrogen, oxygen, nitrogen and sometimes
sulphur
 They are made up of monomers called amino acids
 Some proteins are soluble in water, others are not soluble in water
HOW PROTEINS ARE FORMED
 Proteins are formed when many amino acid units are joined end to end
 There are about 20 different amino acids
 The long chain of amino acids which form proteins can coil up into different shapes
 The way the amino acid chain coils up also determines the 3D shape of the protein
molecule
 The specific order of the amino acids joined determines the shape of the protein
 Different sequences of amino acids give different shapes to protein molecules
PROTEIN SHAPE AND FUNCTION
 The shape of a protein determines its function
 For example the shape of an enzyme creates an active site with a specific shape which
determine the reactions of the enzyme
 The shape of an antibody creates a binding site with a particular shape that can
destroy a particular bacterium or virus
TEST FOR PROTEINS
THE BIURET TEST FOR PROTEINS
OR
USES OF PROTEINS IN LIVING ORGANISMS
 They are used to make enzymes
 They are used to make important parts of cell membranes, mitochondria and
ribosomes
 They are used to make antibodies which destroy bacteria and viruses that enter the
body
 They are used to make haemoglobin in red blood cells
WATER
 Most cells contain about 75 – 80% water
 Cells die if the water content falls below this
 The cytoplasm is a solution of water and dissolved substances
 The spaces between cells is also filled with a watery fluid
 In the cells of all organisms, chemical reactions go on all the time to sustain life
 The reactions that take place in cells all the time are called metabolism
 Metabolic reactions require water in order to occur
IMPORTANCE OF WATER
 It serves as a solvent in which metabolic reactions take place
 It forms an important part of blood plasma
 It is needed to dissolve enzymes and nutrients in the digestive system so that
digestion can occur
 It is needed to get rid of waste products such as urea by the kidneys
VITAMINS
 They are organic molecules that are needed by cells in small amounts to regulate
metabolic reactions
TEST FOR VITAMINS
USE OF VITAMINS IN LIVING ORGANISMS
 They play a very important metabolic reactions in cells and their absence hinders the
cell’s reactions
STRUCTURE OF DNA
 DNA stands for DeoxyriboNucleic Acid
 DNA is the chemical that makes up genes and chromosomes
 It is the material inherited from parents which gives us our characteristics
 It is made up of monomers called nucleotides
 A DNA molecule is made up of two long strands of nucleotide, coiled/twisted together
to form a spiral called a double helix
 Each strand is made up of monomers called nucleotides
 The bases on the two opposite strands are held together by bonds which form crosslinks
 There are four kinds of bases which are adenine (A), thymine (T), cytosine (C) or
guanine (G)
 The bases always pair up in the same way: A with T and C with G
HOW DNA IS USED AS A TOOL FOR CLASSIFICATION
 When molecules of DNA are used to classify species, only one of the two DNA strands
is sequenced
 First the DNA sequence from one strand of a DNA molecule from each species is lined
up against one strand from another species
 The bases of the DNA sequences from the same strand can then be compared with
each other
 The number of differences between the DNA sequences of the species are counted and
recorded
 The most closely related species have the fewest differences between their DNA
sequences
DNA BARCODING
 It is the sequencing of the DNA of one particular gene to help identify different species
of organisms
 The sequences found are called barcodes
IMPORTANCE OR FUNCTIONS OF DNA
 The sequence of the bases in DNA provides a code that determines the sequence of
amino acids in a protein molecule and hence the characteristics of an organism
 It codes for specific proteins
 It stores genetic information
 It can be copied to pass on information to new cells
 It forms genes which determine the characteristics of organisms
END OF CHAPTER
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