Transcript AS Biology - TavistockCollegeScience

AS Biology
Biological molecules
OBJECTIVES
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All should : be able to describe the structure of a water
molecule,the H bonds that hold them together & and
understand this is responsible for its unusual properties.
Be able to describe some of the properties of water and
link some to its structure and importance to living
organisms
Some may: be able to take this a stage further and
give detailed explanations of how the H bonds in water
control the properties that are so important for living
organisms
Unit 2 Module 1 Biological molecules
l
structural proteins
DNA
transport protein
water
Proteins
enzymes
nucleic acids
RNA
saccharides
Unit 2 Module 1 Biological molecules
carbohydrates
lipids
triglycerides
polysaccharides
cholesterol
structural
phospholipids
storage
The Elements of life
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92 naturally occurring elements
The atoms of only 16 are commonly found in living
organisms
4 account for 99% of the atoms found in living
organisms,these are in order of abundance:
H hydrogen
C carbon
O oxygen
N nitrogen
This is because living organisms are made up of organic
molecules
Others are calcium(Ca),iron(Fe),potassium(K),sodium(Na),
chlorine(Cl),sulphur(S) & magnesium(Mg)
Bonding
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Atoms are joined together
to make molecules and
compounds
This is done by chemical
bonds
Most of the molecules
making up living
organisms have atoms
joined by covalent bonds
Covalent bonds are shown
by lines.They can be
single,double or
treble.They are formed by
sharing electrons
Glycine – an amino acid
Covalent bonding
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Carbon always has 4 covalent bonds
with other atoms. Terrestrial life forms
are carbon based. This multiple bonding
allows carbon to be a framework atom
All the biological molecules we will learn
about use carbon as a framework atom.
Other bonds formed are: Oxygen 2
,hydrogen 1 & nitrogen 3
ethanol
ethene
Covalent bonding
The building blocks of life
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Living organisms are mainly made up of
macromolecules (giant molecules)
These are polymers made up of many smaller
monomers by a process called
polymerisation
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The main macromolecules are:
Polysaccharides
Nucleic acids
Proteins (polypeptides)
Lipids (fats)
The Building Blocks of life
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MONOMER
monosaccharide
POLYMER
Organic base,
sugar &
phosphate
Amino
acids
Fatty acids
& glycerol
nucleotides
polysaccharide
Nucleic
acids
proteins
lipids
Carbohydrates
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All contain the elements carbon, hydrogen & oxygen
The name comes from hydrated carbon!
For every carbon atom there is a water
General formula for carbohydrate is
Cn(H2O)n
Q. Fructose has 6 carbons, what is it formula? What
about ribose which is a pentose sugar?
There are 2 types of carbohydrate:
1. Simple sugars: Monosaccharide & Disaccharides
2. Polysaccharides
Simple sugars:
Monosaccharides
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Sugars – all end in -ose
White,crystalline substances,dissolve easily in
water to give sweet solutions.
Single sugar molecule – mono = one
General formula (C H2O)n where n is the
number of carbon atoms
So if 6 carbon atoms(a hexose sugar) the
molecular formula is C6H12O6
What about pentose sugars(C5) or triose
sugars(C3)?
Glucose
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Most important and
widespread
monosaccharide.
Hexose sugar
The 6 carbons are
numbered
Function:Transported
around in the blood and
used in cells as a source of
energy in respiration. The
energy is released in the
form of ATP
Structural formula
1
2
3
4
5
6
Molecular formula
C6H12O6
The ring form of glucose
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The chain of carbons
in hexose(and
pentose) sugars is
long enough to close
up and form a more
stable ring
structure
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Carbon atom 1 joins
to the oxygen on
carbon atom 5
Glucose isomers
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The new OH formed in the reaction can be
above the ring - β glucose or below - α
glucose
These are isomers-two forms of the same
chemical.
Triose,pentose & hexose
sugars
Roles of monosaccharides in
living organisms
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A source of energy for respiration.
Due to large number of C-H bonds which when
broken release a lot of energy
This energy is used to make ATP(adenine
triphosphate) from ADP(adenine diphosphate)
Also used as building blocks to make larger
molecules for example:
Deoxyribose(pentose) used to make DNA
Ribose used to make RNA and ATP
Glucose makes up starch,cellulose and glycogen.
Disaccharide formation
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Two glucose molecules are held close together
by an enzyme.
Water is lost and a 1-4 glycosidic bond(link)
formed .
This is a condensation reaction
The new molecule is a disaccharide - maltose
A disaccharide - maltose
1-4 glycosidic link
Common Disaccharides
Hydrolysis of maltose – by
enzyme maltase
Chemical test for
saccharides(sugars)
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Reducing Sugars
Heat the sugar solution with an equal volume
of blue benedict's solution for 2-3 minutes at
about 90°C
A positive result is a brick red precipitate
Benedicts solution contains blue Cu2+ ions,
the sugar reduces this to the insoluble brick
red Cu+ compound
Cu2+ Electron
Cu+
From sugar
Non reducing sugar test
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Some sugars are non reducing.
They do not reduce benedict's solution
One example is sucrose, it must be
hydrolysed(broken-down by adding
water) to form glucose and fructose
This can be done by heating with a few
drops of acid at 90°C for a few minutes.
Then neutralising the solution with an
equal amount of sodium hydroxide
solution
You will then get a positive result when
repeating the benedict's test
Sugar
lactose
fructose
glucose
sucrose
maltose
Type of
saccharide?
Result of
benedicts test
for reducing
sugar
Result of nonreducing
sugar test
Reducing or
non-reducing
sugar?
Quantitative Estimation of glucose
concentration in a solution
Glucose
solution(%)
0
0.01
0.05
0.1
0.5
1
Weight of
precipitate (g)
Light
Transmission
of filtrate (%)
Sugars homework
a. Glyceraldehyde
– C3 Triose
Ribose
C5 Pentose
Glucose &
Fructose
C6 Hexose
b. Glucose is an
aldose sugar
H-C=O is on C1
c.
d
e alpha glucose OH below the ring
beta glucose OH above ring
f
galactose
alpha
Polysaccharide- Structure &
Function
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Polysaccharides are polymers made up of
monosaccharide subunits
The polymers can be many thousand
monosaccharides – making macromolecules
Most important are starch,glycogen &
cellulose
All are polymers of glucose
They are insoluble in water and do not taste
sweet.
Starch
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Made up of a
mixture of two
macromolecules
Amylose
(20%) and
amylopectin
(80%)
Amylose
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Amylose is formed by condensation of a
long chain of α glucose using 1α – 4
glycosidic bonds
Amylose α helix
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The 1α – 4 glycosidic
links in amylose mean
the glucose monomers
are at a slight angle to
each other
This causes a helix to
form
This is stabilised by
hydrogen bonds
Amylopectin
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Branching chains of α glucose
Branches about once every 25
glucose
Branches formed by 1-6 glycosidic
bonds
The branching structure gives many
“ends” to attach new glucose or to
remove it. So it is ideal for storing
glucose
Starch – Role in living
organisms
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Starch is a store of glucose in plants
Plants cannot store sugars as this would
increase the osmotic potential (low
water potential) of the cells,the solution
inside the cells would be too concentrated.
This would lead to ….
Starch is insoluble and has no osmotic
effect
Starch Grains
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In plants starch is stored
as starch grains
These are most often
found in chloroplasts or
in specialised plant
structures such as seeds
or tubers eg potatoes
The helical shape of
amylose means it can be
packed tightly
Chemical test for Starch
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Add iodine solution to the material
Iodine solution is orange brown
A blue black colour is produced on contact
with starch
This is because the iodine molecules fit into
the amylose helix giving the colour
Glycogen
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Starch is not found in animal
cells
Glycogen is used to store
glucose in animal cells
It is very similar to
amylopectin but more
branched
It branches every 8-10
glucoses,again giving plenty
of ends to add extra glucose
It forms granules which can
be seen in muscle & liver cells
Cellulose
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Cellulose makes up plant cell walls
It is a structural polysaccharide
It is made up of β glucose where OH is above the
ring
In order to form a glycosidic bond the other glucose
must be upside down.
The bond formed is a β1-4 glycosidic bond
Cellulose cross links
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Cellulose cannot form a helix
It exists in long chains
Chains lie side by side and hydrogen bonds form
between them
These form between adjacent glucose molecules and
between the chains.
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This gives the cellulose molecule great mechanical strength
They are insoluble,tough,durable and slightly elastic, ideal structural
components
60-70 chains are strongly linked together to form bundles called
microfibrils
Microfibrils are held together in fibres
Fibres make up the plant cell wall
Structure of cellulose
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Cellulose fibres are laid down in
layers to form the cell wall
Fibres are at right angles to
increase strength
Other molecules help cross
linking
Older cell walls are reinforced
with lignin
A glue like matrix(pectins) is
laid down in between the fibres
to increase strength
Similar to reinforced concrete
Cellulose – structure & function
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High tensile strength of cellulose fibres means
they are difficult to break if pulled at both ends
Allows the cell to withstand the pressure caused
when water enters by osmosis.
Gives plant cells strength and rigidity
Provides support
Despite strength they are freely permeable
Even though cellulose contains glucose it cannot
be digested by most animals as they do not
have the required enzyme cellulase
Other structural polysaccharides
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Chitin
Exoskletons of arthropods
Peptidoglycan
Cell wall of bacterial cells
Lipids
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This group contains a wide range of
molecules ranging from
fats,oils,phospholipids,waxes & steroids
They all contain the elements C,H & O
Normally much less O
The most widespread are TRIGLYCERIDES
also known as fats or oils
Triglyceride structure
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Made up of 3 FATTY ACID molecules
And 1 GLYCEROL molecule
Fatty Acid structure
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Stearic acid an example of a saturated fatty acid.
All the carbon atoms in the tail are full,”saturated” with
hydrogen
Can also be
written as
CH3(CH2)16COOH
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The COOH group is called a
CARBOXYLIC ACID group
The long “tail” of the molecule is called a
HYDROCARBON TAIL
This hydrocarbon chain will not dissolve in
water it is said to be non-polar or
hydrophobic(water hating)
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The carboxylic acid
group is polar or
hydrophilic(water
loving)
Unsaturated Fatty Acids
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These fatty acids
contain a double bond
It causes a “kink” in
the tail
These fatty acids melt
more easily
One double bond is
monounsaturated
More than one are
called polyunsaturated
Glycerol structure
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Glycerol is a type
of alcohol with 3
alcohol groups.
Forming a triglyceride
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When glycerol combines with a fatty acid it
forms a glyceride
When it combines with 3 fatty acids it is a
triglyceride
They combine in a condensation reaction,
losing water
Forming an ester link
Properties
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Triglycerides are insoluble in water, they
are non-polar molecules
The more unsaturated fatty acids the
lower the melting point making these
oils at room temperature, normally found
in plants
Animal fats have a higher melting point
and are generally solid at room
temperature due to saturated fatty acids
Roles of triglycerides
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ENERGY RESERVES- high
number of C-H bonds so
much more energy
content than
carbohydrate-so you need
to store less to get the
same energy
In humans stored around
organs and under the skin
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Stored in adipose tissue
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Under the skin it is
also INSULATION eg
blubber in sea
mammals
It can also produce
metabolic water
when used in
respiration by desert
animals such as
camels
Insoluble: so no
osmotic effect
Phospholipids
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In this molecule the
glycerol has two
fatty acids attached
On the 3rd carbon is
a phosphate group
Phospholipid examples
Phospholipid properties and
roles
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These molecules
have a hydrophobic
tail and hydrophilic
head
They form the
membranes of living
cells
Cholesterol
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Not formed from fatty acids
and glycerol
4 carbon based rings
Small hydrophobic molecule
Found between
phospholipid tails in
membranes
Controls membrane fluidity
and mechanical strength
Excess
cholesterol
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Many cells make
cholesterol from saturated
fats
Especially liver cells
Excess can be deposited in
artery walls
Causing atherosclerosis
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Excess
cholesterol
is removed
in bile
It can form
gallstones
in the gall
bladder
Steroid hormones
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These are made from cholesterol and include:
Chemical test for Lipids
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Emulsion test
Add ethanol to the suspect
material and mix well (any
fat will dissolve in the
alcohol)
Filter off the ethanol
pour the ethanol into water
A milky emulsion will form if
fat was present(fat can no
longer dissolve and forms
small droplets
Proteins(Polypeptides)
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Proteins make up more than 50% of the dry
mass of cells
They have many important functions
All proteins are made up of amino acids
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Functions of proteins
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active
transport
channel
protein
Respiration/
photosynthesis
complex
glycoprotein
membrane
intracellular
(metabolic)
enzymes
Extracellular
(digestive)
Albumin/
globulin
blood
globular
transport
antibodies
hormones
haemoglobin
Proteins in living
organisms
collagen
fibrous
contractile
Actin/myosin
(muscles)
blood
Fibrinogen
(fibrin)
structural
keratin
elastin
Proteins in living
organisms
Amino Acid Structure
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NH2 is the a amine or
amino group
COOH is the carboxylic
acid group
The R group or amino
acid side chain varies.
There are 20 different R
groups found in nature so
giving 20 different
naturally occuring amino
acids
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The 20
naturally
occurring
amino acids
R groups
Amino Acids
The Peptide Bond
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Amino acids are joined together by a
peptide bond
Two amino acids joined form a dipeptide
Peptide bond formation
Polypeptide formation
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Adding more
amino acids to the
chain forms a
polypeptide
In cells this occurs
in ribosomes
A protein molecule
may contain many
hundred AAs and
sometimes more
than one
polypeptide chain
Protein – Primary structure
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The sequence of the
amino acids in the
polypeptide is known as
its primary structure
A protein of several
hundred amino acids has
a huge number of
possible primary
structures
A change in one of the
AAs can completely alter
the properties of the
protein
Protein- Secondary
Structure
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This is when parts
of the polypeptide
chain becomes
twisted or folded
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There are 2 main
types of 2°
structure:
 helix
 pleated sheet
Polypeptide α helix
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Proteins form this
stable helix due to
hydrogen bonding
This takes place
between –C=O of
one A.A
And the –N-H of
the A.A 4 places
ahead
Polypeptide - β Pleated Sheet
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This looser, straighter shape is also formed by H
bonds.
This time between –C=O and –N-H of adjacent
chains
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Proteins may contain both of these secondary
structures
They are easily disrupted by heat & changes in pH
Biological molecules chemical tests
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Reducing Sugars
Heat the sugar solution with an equal volume of blue benedict's solution for 2-3
minutes at about 90°C
A positive result is a brick red precipitate
Non reducing sugar (sucrose)
Collect some filtrate from the reducing sugar test
Add a few drops of acid and heat in a water bath for a few minutes
Neutralise with an equal amount of sodium hydroxide solution
Repeat the benedicts test, a brick red ppt is a positive result
Starch
Add orange brown iodine solution to the material
A blue black colour is produced on contact with starch
Protein
Biuret reagent is made by combining equal amounts of Sodium Hydroxide and
Copper Sulphate
Add biuret reagent to the suspect food or add some dilute sodium hydroxide
solution and mix followed by a little dilute copper sulphate solution.
The copper ions interact with the amino groups in the protein to give PURPLE
colour for a positive result
If the solution stays BLUE this is a negative result
Food Testing
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Starch
Add orange brown iodine solution to the material
A blue black colour is produced on contact with starch
Protein
Biuret reagent is made by combining equal amounts of Sodium
Hydroxide and Copper Sulphate
Add biuret reagent to the suspect food or add some dilute sodium
hydroxide solution and mix followed by a little dilute copper sulphate
solution.
The copper ions interact with the amino groups in the protein to give
PURPLE colour for a positive result
If the solution stays BLUE this is a negative result