Biomolecules: Carbohydrates
Unit 1 Biology
Objectives:
● Discuss that macromolecules are polymers made up of their individual
monomers and formation and breakage of bonds.
● Explain the relationship between the structure and function of glucose.
● Explain the relationship between the structure and function of sucrose.
● Discuss how the molecular structure of starch, glycogen and cellulose
relate to their functions in living organisms.
BIOMOLECULES
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Living organisms are made up of a limited number of types of atoms
which combine to form molecules
These molecules vary in size from simple molecules such as CO2 and H2O
to macromolecules such as proteins. Smaller molecules are soluble and
are easily transported and frequently enter into cells where they can be
used in metabolic processes
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Larger molecules tend to be stored or serve a structural role
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Some of these molecules are used to carry genetic information
Chief Elements Of Organic
Molecules
Ions
Trace Elements
H hydrogen
Na+ Sodium
Mn Manganese
C Carbon
Mg 2+ Magnesium
Fe Iron
N Nitrogen
Cl- Chlorine
Co Cobalt
O Oxygen
K+ Potassium
Cu Copper
P phosphorus
Ca+ Calcium
Zn Zinc
S Sulphur
B Boron
Al Aluminium
Si Silicon
V Vanadium
Mo Molybdenum
I Iodine
Macromolecules
● All living things are made up of four classes of large biological
molecules: carbohydrates, lipids, proteins, and nucleic acids
● Macromolecules are large molecules composed of thousands of
covalently connected atoms
Macromolecules are polymers, built from monomers
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A polymer is a long molecule consisting of many similar
building blocks
These small building-block molecules are called monomers
The Synthesis and Breakdown of Polymers
● A dehydration reaction occurs when two monomers bond together
through the loss of a water molecule
The Synthesis and Breakdown of Polymers
● Polymers are disassembled to monomers by hydrolysis, a reaction that is
essentially the reverse of the dehydration reaction
The Diversity of Polymers
● Each cell has thousands of different macromolecules
● Macromolecules vary among cells of an organism, vary more within a species, and
vary even more between species
● An immense variety of polymers can be built from a small set of monomers
Today’s Lesson
Carbohydrates
Carbohydrates
Carbohydrates include sugars and and contain the elements C, O, H
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Chemical formula Cx(H2O)y
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All carbohydrates :
1.
Are either aldehydes or ketones
2.
Contain several hydroxyl groups
Carbohydrates are divided into 3 classes
1.
Monosaccharides
2.
Disaccharides
3.
Polysaccharides
What is a functional group?
A functional group is a group of atoms in a molecule with distinctive
chemical properties, regardless of the other atoms in the molecule.
Aldehydes and ketones
● Aldehydes and ketones are organic compounds containing the carbonyl group.
● Aldehydes contain the carbonyl group bonded to at least one hydrogen atom.
● Ketones contain the carbonyl group bonded to two carbon atoms.
Carbohydrates
● The simplest carbohydrates are monosaccharides, or single sugars
● Carbohydrate macromolecules are polysaccharides, polymers
composed of many sugar building blocks
Monosaccharides
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Monosaccharides have molecular formulas that are usually
multiples of CH2O
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Glucose (C6H12O6) is the most common monosaccharide
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Monosaccharides are classified by
○ The location of the carbonyl group (as aldose or ketose)
○ The number of carbons in the carbon skeleton
Triose- involved in photosynthesis, form
intermediates in respiration
Pentoses- involved in synthesis of nucleic
acid ribose is found in DNA and RNA,
synthesis of ATP requires ribose. Ribulose
bisphosphate is a CO2 acceptor in
photosynthesis
Hexoses- sources of energy when oxidised
in respiration glucose is the most common
respiratory substrate and the most common
monosaccharide. Synthesizes
disaccharides and polysaccharides
Monosaccharides
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Though often drawn as linear skeletons, in aqueous
solutions many sugars form rings
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Monosaccharides serve as a major fuel for cells and as
raw material for building molecules
The ring forms of glucose molecules
Straight chains and ring forms of fructose
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beta fructose
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alpha fructose
Disaccharides
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A disaccharide is formed when a dehydration reaction(condensation)
joins two monosaccharides usually hexoses this reaction is reversible by
hydrolysis
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This covalent bond is called a glycosidic linkage normally found
between carbon atoms 1 and 4
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Most common disaccharides are:
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Maltose= glucose + glucose
Lactose= glucose + galactose
Sucrose= glucose + fructose
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Maltose:- occurs mainly as a breakdown product during digestion of
starch by enzymes called amylases. This occurs in animals and
germinating seeds. Germination of barley is stimulated by the
conversion of starch to maltose. Maltose is then fermented by yeast to
alcohol
Lactose:- is known as milk sugar is the primary energy source in young
mammals. It is digested slowly so releases energy slowly and steadily
Sucrose:- is formed by plants and is transported in the phloem.
Sucrose is polar and is water soluble. However, it is not as reactive as
glucose and fructose, because the aldehyde and ketone groups form
the glycosidic bond and are not available to react. This lack of reactivity
makes sucrose a non-reducing sugar. It may be an advantage to have
a less reactive sugar for transport in plants as the transport is slower
than those of glucose in animals.
Reducing and non-reducing sugars (video)
Reducing and non-reducing sugars
● All mono and some disaccharides including maltose and lactose are reducing
sugars
● This means they can carry out a type of chemical reaction known as reduction
● Thus Benedict's test and Fehling’s test can be used to test for the presence of
some sugars
Reducing and non-reducing sugars
● Sucrose is a non-reducing sugar. This is because part of the molecule that would react with
the Benedict’s reagent is involved in the glycosidic bond.
● Maltose is a reducing sugar because the two glucose units are linked through carbon 1 and
carbon 4, leaving carbon 1 on the second glucose unit free to form a reducing group.
Why is maltose a reducing sugar?
Polysaccharides
● Polysaccharides, the polymers of sugars, have storage and structural roles
● The structure and function of a polysaccharide are determined by its sugar monomers
and the positions of glycosidic linkages
Storage Polysaccharides
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Starch, a storage polysaccharide of plants, consists entirely of glucose
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Plants store surplus starch as granules within chloroplasts and other
plastids
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Starch is made up of amylose and amylopectin
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Amylose is a straight chain structure consisting of several thousand
glucose residues joined by 1,4 glycosidic bonds
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Amylopectin has twice as much glucose residues as amylose compact
and has many branches with 1,6 glycosidic bonds
monomers
Storage Polysaccharides
● Glycogen is a storage polysaccharide in
animals
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Made from glucose linked through alpha 1-4
glycosidic bonds with alpha 1-6 branches.
Humans and other vertebrates store glycogen
mainly in liver and muscle cells
Storage Polysaccharides
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These organs are the centers of high metabolic activity
where it provides a useful energy reserve
Its conversion is controlled by hormones insulin and
glucagon
Its structure is very similar to amylopectin but shows
more branching
Structural Polysaccharides
● Cellulose a polysaccharide is a major component of the tough wall of plant cells
● Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ
● The difference is based on two ring forms for glucose: alpha (α) and beta (β)
Structural Polysaccharides
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Polymers with α glucose are helical
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Polymers with β glucose are straight
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In straight structures, H atoms on one strand can
bond with OH groups on other strands
Structural Polysaccharides
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Parallel cellulose molecules held together this way are
grouped into microfibrils, which form strong building
materials for plants
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50% of carbon in plants occurs as cellulose and is the
most abundant organic molecules on earth it is also
found in some fungi and non-vertebrate animals
Structural Polysaccharides
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Enzymes that digest starch by hydrolyzing α linkages can’t
hydrolyze β linkages in cellulose
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Cellulose in human food passes through the digestive tract as
insoluble fiber
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Some microbes use enzymes to digest cellulose
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Many herbivores, from cows to termites, have symbiotic
relationships with these microbes
Structural Polysaccharides
● Chitin another structural polysaccharide, is found in the exoskeleton of
arthropods it closely resembles cellulose in structure and function. It forms
bundles of long parallel chains like cellulose
● Chitin also provides structural support for the cell walls of many fungi