The document discusses the structures and roles of biological macromolecules including carbohydrates, lipids, and proteins. Carbohydrates include monosaccharides, disaccharides, and polysaccharides which serve roles as energy sources and building blocks. Lipids such as triglycerides function as energy stores and membrane components. Proteins have complex structures including primary, secondary, tertiary, and quaternary levels which allow them to serve diverse functions essential to life.

1. BIOLOGICAL MOLECULES
The structure of carbohydrates, lipids and
proteins and their roles in living organisms
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2. • Molecular biology: the study of
structure and functioning of biological
molecules
• Metabolism: the sum total of all the
biochemical reactions in the body
• The building blocks of life:
– Hydrogen, carbon, oxygen and nitrogen
– Monosaccharides, organic bases, amino acids,
fatty acids and glycerol
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3. • Macromolecule: ‘giant molecule’
• Polymers (cellulose & rubber; polyester,
PVC & nylon): macromolecules made up of
many repeating subunits that are similar
or identical to each other and are joined
end to end (polymerisation)
– Polysaccharides
– Proteins (polypeptides)
– Nucleic acids (polynucleotide)
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4. Carbohydrates
• Contains carbon, hydrogen and oxygen
• General formula: Cx(H2O)y
• 3 main groups:
– Monosaccharides
– Disaccharides
– Polysaccharides
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5. Monosaccharides
• Sugars (saccharide ~ sweet or sugar)
• General formula: (CH2O)n
– Molecular and structural formula
• Single sugar molecule (mono)
• Types:
– Trioses (3C)
– Pentoses (5C)
– Hexoses (6C)
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7. Ring structures
• α-glucose: the form of glucose where the
hydroxyl group (-OH) on carbon atom 1 is
below the ring
• β-glucose: the form of glucose where the
hydroxyl group (-OH) on carbon atom 1 is
above the ring
• Isomers: 2 forms of the same chemical
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8. Roles of monosaccharides in living
organisms
• Source of energy in respiration (glucose)
– Due to large number of carbon-hydrogen
bonds which can be broken to release energy
• Building blocks for larger molecules
– Glucose: make polysaccharides (starch,
glycogen and cellulose)
– Ribose (a pentose): make RNA and ATP
– Deoxyribose (a pentose): used to make DNA
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9. Disaccharides and glycosidic bond
• Sugars
• Condensation: how 2 monosaccharides join
together to form disaccharides
• Bridge is called glycosidic bonds
• Hydrolisis: addition of water, reverse of
condensation (during digestion of disaccharides
and polysaccharides)
• Both controlled by enzymes
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10. Condensation
Hydrolisis
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11. Polysaccharides
• Not sugars
• Polymers with monosaccharide subunits joined
by condensation with glycosidic bonds
• Several thousand monosaccharide units join to
form a macromolecule
• Most important polysaccharides:
– Starch
– Glycogen Polymers of glucose
– Cellulose
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12. • Glucose is converted to storage
polysaccharides which are convenient,
compact, insoluble molecules
• In the form of starch in plants and glycogen
in animals
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13. Starch, Glycogen and Cellulose
• Starch is a mixture of amylose and
amylopectin
• Amylose: many 1,4-linked α-glucose
molecules form a spring like compact structure
• Amylopectin: 1,4-linked α-glucose but shorter
chains with branching out due to 1,6 linkages
• Starch grains commonly found in chloroplast and
in storage organs such as the potato tuber
and the seeds of cereals and legumes
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14. Amylose
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15. Amylopectin
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16. Glycogen
• No starch in animal cells
• Glycogen: amlyopectin-like molecules used as
the storage carbohydrates
• Glycogen molecules tend to be more branched
than amylopectin
• They clump together to form granules – liver
cells and muscle cells
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17. Glycogen
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18. Cellulose
• Most abundant organic molecule (20-40% of the
average cell wall)
• Structural role (mechanically strong)
• Cellulose is a polymer of β-glucose
• Hydrogen bonds Microfibrils Fibrils
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21. • Very high tensile strength (almost equal to steel)
• Provide support by making tissues rigid
• Responsible for cell expansion during growth
• Freely permeable, allowing water and solutes to reach
plasma membrane
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22. Lipids
• Diverse group of
chemicals
• Triglycerides – most
common type
• Commonly fats and
oils
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23. Triglycerides
• 3 fatty acid + 1 glycerol (condensation)
• -COOH group attached to a hydrocarbon tail
• Glycerol – alcohol
• Glyceride – fatty acid + glycerol (triglyceride)
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24. Condensation
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25. • Insoluble in water but soluble in organic
solvent (ether, chloroform and ethanol)
• Due to hydrocarbon tail of fatty acids
• Non-polar and hydrophobic
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26. Saturated and unsaturated fatty
acids
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27. • Unsaturated – do not contain the maximum
possible amount of hydrogen
• Fatty acids and lipids melt easier due to double
bonds
• Polyunsaturated - >1 double bond
• Monounsaturated - 1 double bond
• Animal lipids – saturated (fats)
• Plant lipids – unsaturated (oils)
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28. Roles of triglycerides
• Energy reserves (richer in carbon-hydrogen
bonds than carbohydrates/higher calorific value)
• Insulator against loss of heat
• Buoyancy
• Metabolic source of water
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29. Desert kangaroo rat
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30. Phospholipids
• One end is soluble in water
• One of the 3 fatty acids is replaced by a
phosphate group which is polar
• Phosphate group is hydrophilic
• Membrane structure
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32. Proteins
• >50% of the dry mass of most cells is protein
• Functions:
– Essential components of cell membranes
– The oxygen-carrying pigment haemoglobin
– Antibodies which attack and destroy invading
microorganisms
– All enzymes
– Hair and the surface layers of skin contain the
protein keratin
– Collagen adds strength to the many tissues,
such as bone and the walls of arteries
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33. Amino acids
• Basic component of protein
• Central carbon atom, amine group (-NH2),
carboxylic acid group (-COOH)
• R group
• 20 different amino acids
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35. The eight amino acids in the orange area are nonpolar and hydrophobic.
The other amino acids are polar and hydrophilic ("water loving").
The two amino acids in the magenta box are acidic ("carboxy" group in the side chain).
The three amino acids in the light blue box are basic ("amine" group in the side chain).
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36. The peptide bond
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37. • 2 linked amino acids – dipeptide
• Many amino acids – polypeptide
(macromolecule/polymer)
• Ribosomes – sites where amino acids are
linked together to form polypeptides
• Complete protein may contain one or
more polypeptide chain which interact
with each other
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38. Primary structure
• The types of amino acids contained in
the polypeptide chain and the
sequence in which they are joined
• Enormous number of different possible
primary structures
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40. Secondary structure
• Polypeptide chain coils into an α-helix due to
attraction between the oxygen of the -CO
group of one amino acid and the hydrogen of
the -NH group of the amino acid four places
ahead of it
• This is result of the polar characteristics of the –
CO and –NH groups
• Sometimes a much looser, straighter shape is
formed, called a β-pleated sheet
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42. Tertiary structure
• The secondary structure coils and folds to
form 3 dimensional shapes
• Four types of bonds involved:
– Hydrogen bonds (between R groups)
– Disulphide bonds (between 2 cysteine
molecules)
– Ionic bonds (between R groups containing
amine and carboxyl groups)
– Hydrophobic interactions (between R
groups which are non-polar or hydrophobic)
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43. Tertiary structure
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44. Quaternary structure
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45. Globular and fibrous proteins
• Globular protein: protein whose molecules curl
up into a ‘ball’ shape (e.g. myoglobin &
haemoglobin)
• Usually curl up so that their non-polar,
hydrophobic R groups point into the centre of
the molecule, away from their watery
surroundings. The polar, hydrophilic, R group
remain on the outside of the molecule
• Fibrous protein: long strands, insoluble and
have structural roles (e.g. keratin & collagen)
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46. Globular and fibrous proteins
e.g. enzymes e.g. keratin and collagen
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47. • Molecular structure and function of
haemoglobin as an example of a globular
protein
• Molecular structure and function of
collagen as an example of a fibrous
protein
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