BIOLOGICAL BIOLOGICAL MOLECULESMOLECULES

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The structure of carbohydrates, lipids The structure of carbohydrates, lipids and proteins and their roles in living and proteins and their roles in living

organismsorganisms

• Molecular biologyMolecular biology: the study of : the study of structure and functioning of structure and functioning of biological moleculesbiological molecules

• MetabolismMetabolism: the sum total of all the : the sum total of all the biochemical reactions in the bodybiochemical reactions in the body

• The building blocks of lifeThe building blocks of life: : – Hydrogen, carbon, oxygen and nitrogenHydrogen, carbon, oxygen and nitrogen– Monosaccharides, organic bases, amino Monosaccharides, organic bases, amino

acids, fatty acids and glycerolacids, fatty acids and glycerol

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• MacromoleculeMacromolecule: ‘giant molecule’: ‘giant molecule’

• Polymers Polymers (cellulose & rubber; (cellulose & rubber; polyester, PVC & nylon): polyester, PVC & nylon): macromolecules made up of many macromolecules made up of many repeating subunits that are similar or repeating subunits that are similar or identical to each other and are joined identical to each other and are joined end to end (polymerisation)end to end (polymerisation)

– PolysaccharidesPolysaccharides– Proteins (polypeptides)Proteins (polypeptides)– Nucleic acids (polynucleotide)Nucleic acids (polynucleotide)

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CarbohydratesCarbohydrates• Contains carbon, hydrogen and oxygenContains carbon, hydrogen and oxygen

• General formula: General formula: CCxx(H(H22O)O)yy

• 3 main groups:3 main groups:– MonosaccharidesMonosaccharides– DisaccharidesDisaccharides– PolysaccharidesPolysaccharides

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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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Ring structuresRing structures

• αα-glucose-glucose: the form of glucose where : the form of glucose where the hydroxyl group (-OH) on carbon the hydroxyl group (-OH) on carbon atom 1 is atom 1 is belowbelow the ring the ring

• ββ-glucose-glucose: the form of glucose where : the form of glucose where the hydroxyl group (-OH) on carbon the hydroxyl group (-OH) on carbon atom 1 is atom 1 is aboveabove the ring the ring

• IsomersIsomers: 2 forms of the same chemical: 2 forms of the same chemical

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Roles of monosaccharides in Roles of monosaccharides in living organismsliving organisms

• Source of energy in respiration (glucose)Source of energy in respiration (glucose)– Due to large number of carbon-hydrogen Due to large number of carbon-hydrogen

bonds which can be broken to release bonds which can be broken to release energyenergy

• Building blocks for larger moleculesBuilding blocks for larger molecules

– Glucose: make polysaccharides (starch, Glucose: make polysaccharides (starch, glycogen and cellulose)glycogen and cellulose)

– Ribose (a pentose): make RNA and ATPRibose (a pentose): make RNA and ATP– Deoxyribose (a pentose): used to make DNADeoxyribose (a pentose): used to make DNA

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• SugarsSugars

• CondensationCondensation: how 2 monosaccharides : how 2 monosaccharides join together to form disaccharidesjoin together to form disaccharides

• Bridge is called Bridge is called glycosidic bondsglycosidic bonds

• HydrolisisHydrolisis: addition of water, reverse of : addition of water, reverse of condensation (during digestion of condensation (during digestion of disaccharides and polysaccharides)disaccharides and polysaccharides)

• Both controlled by Both controlled by enzymesenzymes

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Disaccharides and glycosidic Disaccharides and glycosidic bondbond

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Condensation Condensation

HydrolisisHydrolisis

PolysaccharidesPolysaccharides• Not sugarsNot sugars

• PolymersPolymers with monosaccharide subunits with monosaccharide subunits joined by condensation with glycosidic joined by condensation with glycosidic bondsbonds

• Several thousand monosaccharide units Several thousand monosaccharide units join to form a macromoleculejoin to form a macromolecule

• Most important polysaccharides:Most important polysaccharides:– StarchStarch– GlycogenGlycogen– Cellulose Cellulose

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Polymers of glucosePolymers of glucose

• Glucose is converted to Glucose is converted to storage storage polysaccharidespolysaccharides which are convenient, which are convenient, compact, insoluble moleculescompact, insoluble molecules

• In the form of In the form of starch in plantsstarch in plants and and glycogen in animalsglycogen in animals

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Starch, Glycogen and Starch, Glycogen and CelluloseCellulose

• Starch is a mixture of Starch is a mixture of amylose amylose and and amylopectinamylopectin

• Amylose: many Amylose: many 1,4-linked 1,4-linked αα-glucose-glucose molecules form a spring like compact molecules form a spring like compact structurestructure

• Amylopectin: Amylopectin: 1,4-linked 1,4-linked αα-glucose-glucose but but shorter chains with branching out due to shorter chains with branching out due to 1,6 1,6 linkageslinkages

• Starch grains commonly found in chloroplast Starch grains commonly found in chloroplast and in and in storage organsstorage organs such as the potato such as the potato tuber and the seeds of cereals and legumestuber and the seeds of cereals and legumes

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Amylose Amylose

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Amylopectin Amylopectin

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GlycogenGlycogen• No starch in animal cellsNo starch in animal cells

• Glycogen: Glycogen: amlyopectin-likeamlyopectin-like molecules molecules used as the used as the storage carbohydratesstorage carbohydrates

• Glycogen molecules tend to be Glycogen molecules tend to be more more branchedbranched than amylopectin than amylopectin

• They clump together to form They clump together to form granulesgranules – – liver cells and muscle cells liver cells and muscle cells

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GlycogenGlycogen

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CelluloseCellulose

• Most abundant organic molecule (20-40% Most abundant organic molecule (20-40% of the average cell wall)of the average cell wall)

• Structural roleStructural role (mechanically strong) (mechanically strong)

• Cellulose is a Cellulose is a polymer of polymer of ββ-glucose-glucose

• Hydrogen bondsHydrogen bonds MicrofibrilsMicrofibrils FibrilsFibrils

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• Very high Very high tensile strengthtensile strength (almost equal to steel) (almost equal to steel)

• Provide supportProvide support by making tissues rigid by making tissues rigid

• Responsible for Responsible for cell expansioncell expansion during growth during growth

• Freely permeableFreely permeable, allowing water and solutes to , allowing water and solutes to reach plasma membranereach plasma membrane

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Lipids Lipids

• Diverse group of Diverse group of chemicalschemicals

• TriglyceridesTriglycerides – – most common typemost common type

• Commonly fats and Commonly fats and oilsoils

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TriglyceridesTriglycerides

• 3 fatty acid + 1 glycerol (3 fatty acid + 1 glycerol (condensationcondensation))

• -COOH-COOH group attached to a hydrocarbon tail group attached to a hydrocarbon tail

• GlycerolGlycerol – alcohol – alcohol

• GlycerideGlyceride – fatty acid + glycerol – fatty acid + glycerol ((triglyceridetriglyceride))

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CondensationCondensation

• Insoluble in water but soluble in Insoluble in water but soluble in organic solvent (ether, chloroform and organic solvent (ether, chloroform and ethanol)ethanol)

• Due to hydrocarbon tail of fatty acidsDue to hydrocarbon tail of fatty acids

• Non-polar and hydrophobicNon-polar and hydrophobic

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Saturated and unsaturated Saturated and unsaturated fatty acidsfatty acids

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• UnsaturatedUnsaturated – do not contain the – do not contain the maximum possible amount of hydrogenmaximum possible amount of hydrogen

• Fatty acids and lipids Fatty acids and lipids melt easiermelt easier due to due to double bondsdouble bonds

• PolyunsaturatedPolyunsaturated - >1 double bond - >1 double bond

• MonounsaturatedMonounsaturated - 1 double bond - 1 double bond

• Animal lipids – saturated (fats)Animal lipids – saturated (fats)

• Plant lipids – unsaturated (oils) Plant lipids – unsaturated (oils)

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Roles of triglyceridesRoles of triglycerides

• Energy reserves (richer in carbon-hydrogen Energy reserves (richer in carbon-hydrogen bonds than carbohydrates/higher calorific bonds than carbohydrates/higher calorific value)value)

• Insulator against loss of heatInsulator against loss of heat

• BuoyancyBuoyancy

• Metabolic source of waterMetabolic source of water

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Desert kangaroo ratDesert kangaroo rat

PhospholipidsPhospholipids

• One end is soluble in waterOne end is soluble in water

• One of the 3 fatty acids is replaced One of the 3 fatty acids is replaced by a phosphate group which is polarby a phosphate group which is polar

• Phosphate group is hydrophilicPhosphate group is hydrophilic

• Membrane structureMembrane structure

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ProteinsProteins• >50% of the dry mass of most cells is protein>50% of the dry mass of most cells is protein• Functions:Functions:

– Essential components of cell membranesEssential components of cell membranes– The oxygen-carrying pigment haemoglobin The oxygen-carrying pigment haemoglobin – Antibodies which attack and destroy Antibodies which attack and destroy

invading microorganisms invading microorganisms – All enzymesAll enzymes– Hair and the surface layers of skin contain Hair and the surface layers of skin contain

the protein keratinthe protein keratin– Collagen adds strength to the many Collagen adds strength to the many

tissues, such as bone and the walls of tissues, such as bone and the walls of arteries arteries

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Amino acidsAmino acids

• Basic component of proteinBasic component of protein

• Central carbon atom, amine group (-Central carbon atom, amine group (-NHNH22), carboxylic acid group (-COOH)), carboxylic acid group (-COOH)

• R groupR group

• 20 different amino acids20 different amino acids

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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).

The peptide bondThe peptide bond

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• 2 linked amino acids – dipeptide2 linked amino acids – dipeptide

• Many amino acids – polypeptide Many amino acids – polypeptide (macromolecule/polymer)(macromolecule/polymer)

• Ribosomes – sites where amino acids Ribosomes – sites where amino acids are linked together to form are linked together to form polypeptidespolypeptides

• Complete protein may contain one or Complete protein may contain one or more polypeptide chain which interact more polypeptide chain which interact with each otherwith each other

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Primary structurePrimary structure

• The types of amino acids The types of amino acids contained in the polypeptide chain contained in the polypeptide chain and the sequence in which they and the sequence in which they are joinedare joined

• Enormous number of different Enormous number of different possible primary structurespossible primary structures

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Secondary structureSecondary structure• Polypeptide chain coils into an Polypeptide chain coils into an αα-helix-helix due due

to attraction between the oxygen of the to attraction between the oxygen of the -CO group of one amino acid and the -CO group of one amino acid and the hydrogen of the -NH group of the amino hydrogen of the -NH group of the amino acid four places ahead of itacid four places ahead of it

• This is result of the polar characteristics of This is result of the polar characteristics of the –CO and –NH groups the –CO and –NH groups

• Sometimes a much looser, straighter Sometimes a much looser, straighter shape is formed, called a shape is formed, called a ββ-pleated -pleated sheetsheet

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Tertiary structureTertiary structure• The secondary structure coils and The secondary structure coils and

folds to form 3 dimensional shapesfolds to form 3 dimensional shapes

• Four types of bonds involved:Four types of bonds involved:– Hydrogen bondsHydrogen bonds (between R groups) (between R groups)– Disulphide bondsDisulphide bonds (between 2 cysteine (between 2 cysteine

molecules)molecules)– Ionic bondsIonic bonds (between R groups (between R groups

containing amine and carboxyl groups)containing amine and carboxyl groups)– Hydrophobic interactionsHydrophobic interactions (between R (between R

groups which are non-polar or groups which are non-polar or hydrophobic)hydrophobic)

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Tertiary structureTertiary structure

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Quaternary structureQuaternary structure

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• Globular proteinGlobular protein: protein whose molecules : protein whose molecules curl up into a ‘ball’ shape (e.g. myoglobin & curl up into a ‘ball’ shape (e.g. myoglobin & haemoglobin)haemoglobin)

• Usually curl up so that their non-polar, Usually curl up so that their non-polar, hydrophobic R groups point into the centre of hydrophobic R groups point into the centre of the molecule, away from their watery the molecule, away from their watery surroundings. The polar, hydrophilic, R group surroundings. The polar, hydrophilic, R group remain on the outside of the moleculeremain on the outside of the molecule

• Fibrous proteinFibrous protein: long strands, insoluble and : long strands, insoluble and have structural roles (e.g. keratin & collagen)have structural roles (e.g. keratin & collagen)

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Globular and fibrous proteinsGlobular and fibrous proteins

Globular and fibrous Globular and fibrous proteinsproteins

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e.g. enzymese.g. enzymes e.g. keratin and collagene.g. keratin and collagen

• Molecular structure and function of Molecular structure and function of haemoglobin as an example of a haemoglobin as an example of a globular proteinglobular protein

• Molecular structure and function of Molecular structure and function of collagen as an example of a fibrous collagen as an example of a fibrous proteinprotein

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