CARBOHYDRATES
Simple and complex
sugars
▪ 1.3. Explain the relationship between the structure and
function of glucose
▪ Exact molecular ring structure in full
▪ Distinguish between the structures of alpha and beta
glucose
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▪ A group of organic compounds whose molecules contain
atoms of carbon, hydrogen and oxygen only.
▪ Are hydrates of carbon
▪ The ratio of hydrogen atoms to oxygen atoms is always
2:1
▪ General formula: 𝐶𝑥 𝐻2 𝑂
𝑦
▪ They are the most abundant organic molecules.
▪ They are the primary energy storage molecules in most
organisms.
▪ Energy is released when the covalent bonds are broken.
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▪ Monosaccharides – These contain a single sugar
molecule (e.g. glucose & fructose)
▪ Disaccharides – these are made up of two sugar
molecules linked by a covalent bond. (e.g. sucrose)
▪ Polysaccharides – large molecules made of many
sugar units sugar units linked together.
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▪ Are the simplest types of carbohydrates
▪ Their general formula is (CH2O)n,
▪ n can be any number from 3 – 7.
▪ Have the same number of carbon atoms as oxygen
atoms in the molecule
▪ They all contain a ketone or aldehyde functional group.
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▪ They are named according to number of carbons in
their structure or their functional group
▪ They are soluble
▪ Dissolve in water to give sweet tasting solutions
▪ Once in solution, they readily reduce other chemicals
and are called reducing sugars.
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According to number of
carbons:
According to functional
group.
▪ Triose – 3 carbons
▪ Aldose – has an aldehyde
▪ Tetrose – 4 carbons
▪ Pentose – 5 carbons
▪ Hexose – 6 carbons
functional group (-CHO)
▪ Ketose – has a ketone
functional group ( -C=O)
▪ Heptose – 7 carbons
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Glyceraldehyde
Dihydroxyacetone
Triose
Triose
Aldose
Ketose
The structural formulae are given what are the molecular formulae
for these trioses? What is the relationship between these two
sugars?
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Aldose
Ketose
Hexose
Hexose
Glucose
Fructose
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▪ An oxidation-reduction (redox) reaction is a type of
chemical reaction that involves a transfer of electrons
between two species
▪ When a substance such as a sugar, reduces another
chemical, it takes oxygen, or electrons, from that chemical
or donates hydrogen to it.
▪ In doing this, the substance or sugar becomes oxidized.
▪ Oxidation Is Loss of electrons
▪ Reduction Is Gain of electrons
▪OIL RIG
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▪ When in solution they have a free aldehyde or ketone
group.
▪ They are able to supply electrons and therefore act as
reducing agents.
▪ They are identified by their ability to reduce Cu2+ to
Cu+, this is seen as a change from blue to brick red.
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Both these forms of glucose are able to donate electrons and act
as a reducing agent.
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▪ Hexoses are the main source of energy for a living
organism
▪ Glucose, fructose and galactose
▪ Compounds with the same molecular formula but a
different arrangement of atoms are called isomers.
▪ Same molecular formula, different structural
formulae
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▪ The most common monosaccharide.
▪ Molecular formula: C6H12O6
▪ It is highly soluble.
▪ It is the primary respiratory substrate of cells.
▪ It is the only respiratory substrate of brain cells.
▪ It can be used to synthesise other biomolecules.
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▪ Isomers are molecules with the same chemical formula
but different structural formulae
▪ Glucose can exist in 2 ring forms. These are referred to
as the alpha (α) and beta (β) forms
▪ α glucose: the hydroxyl group on carbon 1 projects
below the ring
▪ β glucose: the hydroxyl group on carbon 1 projects
above the ring
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https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjZttKVi
cXdAhVphAKHWtfDi0QjRx6BAgBEAU&url=https%3A%2F%2Fthebiochemgazette.wordpress.com%2Ftag%2Fpolysaccharide
%2F&psig=AOvVaw2OQcG1aGTdQbIOYrQiNlZT&ust=1537374490146747
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http://bio1151.nicerweb.com/Locked/media/ch05/glucose.html
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▪ Molecular formula: C6H12O6
▪ Sweetest of all the naturally occurring sugars
▪ Found in fruits vegetables and honey
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https://slideplayer.com/slide/4450347/14/images/10/Haworth+Structure+of+Fructose.jpg
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▪ Molecular
formula: C6H12O6
▪ Found in dairy
products, avocad
os, sugar beets
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▪ 1.2. Discuss that macromolecules are polymers made
up of their individual monomers and formation and
breakage of bonds
▪ 1.4.Explain the relationship between the structure and
function of sucrose
▪ Exact molecular ring structure in full
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▪ Condensation
▪ Two smaller molecules join together to form a larger
molecule. One molecule of water is released:
AOH + BH
AB + H2O
▪ Hydrolysis
▪ A large molecule reacts with water and splits into two
smaller ones:
AB + H2O
AOH + BH
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▪ Are formed when 2 monosaccharides react together by
means of a condensation reaction
Condensation
C6H12O6 + C6H12O6
C12H22O11 + H2O
Hydrolysis
▪ The covalent bond produced is known as a glycosidic
linkage.
▪ Glycosidic linkages are found in disaccharides and
polysaccharides.
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1 – 4 glycosidic
1 -6 glycosidic
▪ Formed between C1 and
▪ Formed between C1 and
▪ Is found in disaccharides
▪ Is found in molecules that
▪ Examples: Maltose,
▪ Example: glycogen and
C4 of successive
monomer units.
and un-branched chains.
amylose a constituent of
starch.
C6 of successive
monomer units.
have branched chains
amylopectin.
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http://web.sls.hw.ac.uk/teaching/Derek_J/A1
3MM1web/Lectures/files/polysaccharides/index.ht
http://namrataheda.blogspot.com/2013/04/bi
ml
omolecules-of-cell-carbohydrates31
part_16.html
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https://socratic.org/questions/can-anyone-explain-to-me-how-to-identifyepimers-and-anomers-in-carbohydrates-su
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https://illuminolist.wordpress.com/tag/d-l-designation/
The formation of maltose
http://oregonstate.edu/instruction/bi3
14/summer09/chemone.html
The formation of sucrose
http://cnx.org/contents/185cbf87c72e-48f5-b51ef14f21b5eabd@9.45:11
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▪ The most common non-reducing sugar
▪ It is highly soluble
▪ It is chemically inert.
▪ It is the form in which plants transport their food.
▪ Formed when alpha-glucose condenses with fructose
▪ Molecular formula: C12H22O11
▪ Harvested from the stems of sugar cane (Saccharum
officinarum)
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▪ Draw on board
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▪ 1.5. Discuss how the molecular structure of starch,
glycogen and cellulose relate to their functions in
living organisms
▪ Molecular structure
▪ Types of bonds
▪ Chain and ring structure where appropriate
▪ 3D nature
▪ Hydrolysis and condensation reactions
▪ Relate structure to properties
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▪ A polymer of α-glucose
▪ It is the primary storage polysaccharide in plants
▪ Is not found in animals
▪ Has compact & insoluble molecules therefore ideal for in which
to store glucose molecules and these can be reformed by
hydrolysis when needed
▪ Made up of two different forms
▪ Amylose (20 – 30%)
▪ Amylopectin (70 – 80%)
▪ Starch can be found in tubers, leaves and the endosperm of
seeds(wheat)
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▪ Has compact & insoluble molecules therefore ideal for in which
to store glucose molecules and these can be reformed by
hydrolysis later, when needed.
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▪ Linear, un-branched chain that forms a helix.
▪ One molecule may contain about 1000 α-glucose residues.
▪ What bonds exist between the monomer units?
▪ The bonds cause the chains to coil helically
▪ Due to the long un-branched chains amylose can be
compacted making it a good storage molecule
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https://www.smartkitchen.com/resources/amylose
▪ Many alpha-glucose molecules condense together forming 1,4
glycosidic bonds, producing long unbranched chains.
▪ These chains take a helical (coiled) configuration as each
monomer has a bulky side group which has to be
accommodated.
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▪ Contain 1000 – 6000 or more α-glucose residues.
▪ Short chains of 8 – 12 units branch of the main chain every 24 –
30 monomers.
▪ At every branch point there is an α- 1,6 glycosidic bond.
▪ Amylopectin is insoluble in water due to the cross-links
between adjacent hydroxyl groups.
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https://www.smartkitchen.com/resources/amylopectin
http://www1.lsbu.ac.uk/water/starch.html
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▪ The common storage polysaccharide in prokaryotes, fungi and
animals.
▪ The animal equivalent of starch
▪ Consist of a main chain with branches every 8 – 12 α-glucose
residues
▪ Glycogen branches (with α-1,6 glycosidic linkages) more
extensively than starch
▪ The branching makes glycogen very dense which makes it
easy to store in liver and muscle cells
▪ Energy reserve
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https://glossary.periodni.com/glossary.php?en=glycogen
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http://physicalrules.com/2017/05/glycogen-storage-depletion-and-repletion-week-1/
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▪ The parallel chains of β-glucose interact with each other via
hydrogen bonding
▪ The OH groups projecting above and below the molecule
hydrogen bond with each other giving cross-linkages
▪ The repeated hydrogen bonds make cellulose very difficult to
digest, stretch or compress
▪ Cellulose is indigestible by humans
▪ Cellulose makes plant cell walls semi-rigid
▪ Once glucose is incorporated into plants cell walls as cellulose
it is unavailable to the plant as an energy source
▪ Hundreds of cellulose chains bundle together in units called
microfibrils
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▪ When two beta-glucose molecules condense together forming
1,4- glycosidic bonds, alternate molecules are rotated 180
degrees allowing the appropriate –OH groups to react.
▪ This has two effects:
1.
The unbranched chains are straighter as the bulky side
groups have to be accommodated on opposite sides
alternately
2.
Hydrogen bonds are formed between the -OH groups and
oxygen of adjacent straight chains. This gives cellulose a
strong, fibrous structure.
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▪ Cellulose has very different properties from starch or
glycogen.
▪ It does not form grains or small granules and its role is not
storage but structural.
▪ It is fibrous and strong and is the major component of plant cell
walls.
▪ This difference reflects the fact that, unlike starch or glycogen,
the monomer of cellulose is beta-glucose.
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▪ The parallel cellulose molecules form bundles known as
microfibrils and these in turn cluster into microfibrils with
immense tensile strength and stability.
▪ The bundles are arranged in a gel-like matrix of other smaller
polysaccharides in plant cell walls.
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http://botanystudies.com/the-cell-wall-and-its-structure/cellulose-structure/
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https://socratic.org/questions/595f411111ef6b615ef01270
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▪ Independent Reading!!!!!!!!
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▪ All monosaccharides, and some disaccharides including lactose
and maltose
▪ Benedict’s test and Fehling’s test
▪ Involves copper (II) sulphate solution
▪ Reducing sugars reduce copper from a valency of 2 to a valency of 1
▪ Copper (II) sulphate (CuSO4) is reduced to copper (I) oxide (Cu2O)
Ionic equation:
Cu2+ + e-
Cu+
Blue solution
Brick red precipitate
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▪ Sucrose is the only common non-reducing sugar
▪ Must be hydrolysed first by dilute hydrochloric acid
▪ Acid must be neutralized by adding sodium hydrogen
carbonate (NaHCO3)
▪ Benedict’s test is then carried out
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▪ Contains amylose and amylopectin
▪ Solution to detect starch contains iodine (I2) and potassium
iodide (KI) and is written as I2/KI.
▪ Forms a polyiodide complex with starch
▪ Food test solution changes from colourless to blue-black if
starch is present
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