Carbon based life
• Where is carbon on the periodic table?
• How many electrons does it have in its outer
shell?
• How many covalent bonds can it form?
• Being able to form 4 covalent bonds carbon
can be the basis of complex molecules –
long chains, rings and these can include
single, double or triple bonds. This
molecular complexity is vital to life.
Lesson objectives:
By the end of this session pupils should be able to....
• Describe, with the aid of diagrams, the molecular
structure of alpha-glucose as an example of a
monosaccharide carbohydrate.
• State the structural differences between alpha
and beta glucose.
• Describe with the aid of diagrams, the structure of
glycogen
• Describe with the aid of diagrams the formation
and breakage of glycosidic bonds (maltose and
amylose)
Four types to look at
•
•
•
•
Water
Carbohydrates
Lipids
Proteins
Revise anything
you know about all
of these from
GCSE!
Elements involved
• The big three – C, H and O
• Others that turn up frequently – N, P and S
• There are small amounts of others too e.g.
minerals – Ca, K, Na, Cl, Mg
• Can you name any instances we have met
already where these elements are involved?
Hydrogen atom
Stereoisomers
These are molecules that have the same physical
and chemical properties except that they are
mirror images of each other
S
C
H
NH₂
OH
This occurs because of the tetrahedral position of the 4
covalent bonds that carbon forms. To create a stereoisomer
the carbon must be bonded to 4 different groups
Why are stereoisomers significant in biological reactions?
Properties of monosaccharides
• Soluble in water
• Sweet tasting
• Form crystals
General formulae:
Cn(H2O)n
Hydrated carbon!
Classification of Monosaccharides
Monosaccharide = a single sugar (MONOMER)
Grouped according to number of Carbon atoms
in the molecule:
• 3-carbon monosaccharides = triose sugar
• 5-carbon monosaccharides = pentose sugars
• 6-carbon monosaccharides = hexose sugar
Which group does glucose belong to?
Glucose:
Alpha (α)
Glucose
beta (β)
REMEMBER: beta (β) glucose has the Hydrogen atom
at the bottom as you look at the structural diagram
6
5
4
1
3
2
Joining monosaccharides & splitting
disaccharides
• Condensation reactions (join sugars)
• Hydrolysis reaction (break sugars
Glycosidic
apart) bond
Properties of Disaccharides
• Soluble
• Sweet
• Crystalline
• Types of disaccharide
• α glucose + α glucose = maltose
• α glucose + fructose = sucrose
• α glucose + galactose = lactose
• Roles of Disaccharides
• Maltose: breakdown product of starch, found in malt barley
• Sucrose: transport of sugars in phloem. Glucose converted to
sucrose
• Lactose: Found in milk. Energy source for babies
Polysaccharides (POLYMER)
(long chain carbohydrates)
• Starch
(main storage material in plants)
• Glycogen
(the main storage material in animals)
• Cellulose
(major structural components of cell walls in
plants)
Starch
(Plants)
Made up of alpha glucose
Two forms
• Amylose
Unbranched helix
• Amylopectin
Branched structure
Lets try to draw amylose!
Glycogen (animals)
• Branches much more than
amylopectin
• Made up from
alpha glucose
subunits.
• 1-4 linked glucose
chains tend to be shorter than for starch.
1: 6 bonds more frequently
Structure and function
Insoluble
•So doesn’t affect osmosis of the cell. H groups and OH groups
tucked inside coils, so won’t form H bonds with water.
Starch
Amylose – coiled structure,
compact, good for storage.
Amylopectin
• branched chain of alpha
glucose.
• large surface area
• Many ends – highly
efficient energy store and
release
Glycogen
• Highly branched
• Large surface area
• Many ends – highly
efficient energy store and
energy release.
How are we doing?
1. What is the name given to the type of bond
that holds sugar molecules together?
2. Name the two different types of molecule
which are joined together in a starch
molecule.
3. Explain why starch and glycogen are good
stores of energy.
Stretch and challenge!
1. Draw a diagram to show how a maltose
molecule is formed from the end of amylose.
Name the enzyme that catalyses the reaction
Lesson objectives: so can we?
By the end of this session pupils should be able to....
• Describe, with the aid of diagrams, the molecular
structure of alpha-glucose as an example of a
monosaccharide carbohydrate.
• State the structural differences between alpha and
beta glucose.
• Describe with the aid of diagrams, the structure of
glycogen
• Describe with the aid of diagrams the formation and
breakage of glycosidic bonds (maltose and amylose)
What about cellulose?
Cellulose
• The most abundant organic molecule on the
planet 20-40% of cell walls
• Polymer of β-glucose straight, unbranched
chains
• Insoluble in water
• Indigestible by vertebrates (mutualistic
microorganisms in herbivores produce cellulase
• Structural role due to mechanical strength
caused by hydrogen bonding
• 60-70 cellulose molecules become tightly
crosslinked to form microfibril bundles
• Microfibrils held together in bundles called
fibres
• Prevents plant cells bursting.