Transcript Unit 1 overview

Unit 3 Biological
Molecules
AS Unit F212
Context
Proteins, carbohydrates and lipids are 3 of
the key groups of macromolecules
essential for life
 Understanding the structure of these
macromolecules allows an understanding
of their functions in living organisms
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Objectives
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Describe how hydrogen bonding occurs
between water molecules, and relate this,
and other properties of water to the roles
of water in living organisms
Covalent Bonding
Bonding between non-metals
 Consists of atoms sharing electrons
 The electrons are in the outer shell
 Strong bonds, lot of energy is required to
break them
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The number of covalent bonds is equal to eight minus
the group number
Hydrogen Bonding
Water- a special case
Covalent bonding is an electron sharing bond, and in this case the sharing is not
equal. The oxygen gets more, giving it a slightly -ve charge δ- .
Water as a solvent
Water is an excellent solvent.
 The tiny charges attract other molecules.
 The other molecules and ions spread
around in between the water molecules.
 This is called dissolving
 Many reactions, including metabolic
reactions will only take place in solution
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Density and viscosity
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Water molecules are pulled together by
the hydrogen bonds between them, this
makes water a relatively dense liquid.
 Why
is it easy for living organisms to swim?
 How might an organism have adapted to float
or sink in water?
 How have organisms adapted to swim?
Cohesion and
surface tension

Water molecules tend to stick together, this is called
cohesion. Even in a tall column of water, forces holding the
molecules to each other help to prevent the column from
breaking.
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Within water each molecule is attracted to all the molecules
around it. On the surface the uppermost molecules only
have the molecules underneath so are pulled downwards.
Surface Tension forming a strong layer on the surface of
water.
How does cohesion help with water
transport in a plant?
Water moves up each column by mass
flow. Cohesion between the water
molecules hold the column together.
 If the column broke, then the pulling force
exerted by transpiration in the leaves
would not be transmitted to the whole of
the column and the water would not move
up the plant in this way.
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Property
Key Points
Role of water
Good solvent for
charged and
uncharged substances
Water molecules are attracted to ions
and polar molecules e.g glucose
Transport in blood, xylem and phloem
Specific heat capacity
is high
4.2kj are necessary to increase the
temperature of water by 1oC
The thermal energy absorbed is used
to break the hydrogen bonds
Helps prevent changes in body temperature
Latent heat of
vaporisation is high
Much thermal energy is used to
cause water molecules to change to
water vapour- this happens in
transpiration in plants, and in
sweating and painting in mammals
Coolant- water is used efficiently, as a small
amount of water absorbs much thermal energy
High cohesion
Hydrogen bonds ‘stick’ water
molecules together
Helps draw up water in xylem
Can be reactive
Water reacts with other substances
Involved in hydrolysis reactions an in
photosynthesis
Incompressibility
Outside pressure cannot force water
into a smaller space
Hydrostatic skeleton for some animals e.g.
earthworms
Provides turgidity in plant cells
Starter activity
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Firstly, peer assess each others work using
the markscheme provided.
Mark with 2 stars and a wish
State four functions of water in living organisms
Briefly describe a water molecule
Briefly describe what is meant by a polar
molecule
Why is water’s high specific heat capacity useful
for living organisms?
Starter activity
State four functions of water in living
organisms
 Briefly describe a water molecule
 Briefly describe what is meant by a polar
molecule
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 A molecule
is polar if it has a negatively
charged part and a positively charged part
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Why is water’s high specific heat capacity
useful for living organisms?
Exam question
Water is essential for life. It makes up a high proportion of the cytoplasm
in a cell. Many different compounds can dissolve in it and it is therefore
described as an excellent
.
Water remains in the
state over a wide range of
environmental temperatures. As it cools below 4 °C it becomes less
than warmer water. Ice floats on water, forming
a layer that
the water beneath with the result that
large bodies of water rarely freeze entirely.
The
bonds that form between water molecules are
responsible for its high
, which allows small
insects such as pond skaters to move on its surface without sinking.
Exam question
Water is essential for life. It makes up a high proportion of the cytoplasm
in a cell. Many different compounds can dissolve in it and it is therefore
described as an excellent
.
Solvent
Water remains in the
state over a wide range of
liquid
environmental temperatures.
As it cools below 4 °C it becomes less
than warmer water. Ice floats on water, forming
a layer that
the water beneath with the result that
dense
insulates
large bodies of water
rarely freeze entirely.
The
bonds that form between water molecules are
hydrogen
responsible
for its high
, which allows small
Surface
tension
insects such as pond skaters
to move
on its surface without sinking.
8 marks
You have been given an a sample of an
unknown solution. Your task is to find out
what biological molecules have been
dissolved in the water.
 You must write a method for each
biological test you carry out and a table of
the results you collect.
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Condensation and hydrolysis reactions
Objectives
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Describe with the aid of diagrams, the
molecular structure of
 alpha-glucose
 Beta
glucose
 Maltose
 Amylose
 Glycogen
 Cellulose
Learning outcomes
Describe, with the aid of diagrams, the
molecular structure of alpha glucose as an
example of a monosaccharide
carbohydrate
 State the structural difference between
alpha and beta glucose
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Week 13
Subunit structure of amylose and glycogen
© Pearson Education Ltd 2008
This document may have been altered from the original
Key terms
Monosaccharide
 Disaccharide
 Polysaccharide
 Monomer
 Polymer
 Condenastion
 Hydrolysis
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Learning outcomes
Describe, with the aid of diagrams, the
formation and breakage of glycosidic
bonds in the synthesis and hydrolysis of a
disaccharide (maltose) and a
polysaccharide (amylose)
 Compare and contrast the structure and
functions of starch (amylose) and
Cellulose
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Learning Outcomes
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Explain how the structures of glucose,
starch (amylose), glycogen and cellulose
molecules relate to their function in living
organisms
describe, with the aid of diagrams, the
structure of an amino acid
 describe, with the aid of diagrams, the
formation and breakage of peptide bonds
in the synthesis and hydrolysis of
dipeptides and polypeptides;
 explain, with the aid of diagrams, the term
primary structure;
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Amino Acid structure
H
H
N
H
Amine Group
C
R
O
C
OH
Carboxylic Acid group
R group
Changes for each amino acid
H
H
N
C
H
O
N
H
+
C
R
H
H
OH
H
N
C
H
H
H2O
O H
H
C
C
C
N
R
Peptide Bond
R
R
O
C
OH
O
C
OH
Condensation
Reaction
Objectives
explain, with the aid of diagrams, the term
quaternary structure, with reference to the
structure of haemoglobin;
 describe, with the aid of diagrams, the
structure of a collagen molecule;
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Description or Diagram
Primary
structure
Secondary
Structure
Tertiary
Structure
Quaternary
Structure
Examples
Haemoglobin
4 polypeptides in each
haemoglobin
2 x α globin subunits
2x β globin subunits
Secondary structure- α helix
Tertiary structure- further folding
of polypeptide stabilised by
hydrophobic interactions
Quaternary structure
An example of a Globular protein
Made of 4 polypeptide chains
which fit together and are held in
place by hydrogen bonds and
ionic bonds between R groups
In the middle of each subunit is a haem group. Each haem group can combine
with 1 molecule of oxygen so each molecule of haemoglobin can combine with
4 molecules of oxygen
Collagen
3 identical chains per
molecule of collagen
All wound around each
other forming a triple helix
Each chain consists of
about 1000 amino acids
Primary structure- every 3rd
a.a. is glycine, smallest
Rgroup (1H)
An example of a fibrous protein
Collagen doesn’t show secondary, tertiary, or
quaternary structure in the same way as globular
proteins
The sequences are
staggered to allow glycine
to be found at every
position
This allows the 3 chains to
pack closely together,
forming many hydrogen
bonds
Collagen
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The triple helix is left handed
 αhelix
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has a right hand turn
No further folding to give 3d shape
Adjacent molecules form covalent bonds
between Rgroups
Collagen forms fibres
Crosslinks and hydrogen bonds give collagen its
strength
Globular and fibrous proteins
Globular proteins
Examples Haemoglobin, enzymes,
Fibrous proteins
Collagen, keratin, elastin
antibodies, transporters in
membranes, some hormones
(e.g. insulin)
Primary
structure
Very precise, usually made of a
non-repeating sequence of
amino acids forming a chain that
is always the same length
Often made up of a repeating
sequence of amino acids, and
the chain can be of varying
length
Solubility
Often soluble in water
Insoluble in water
Functions Usually metabolically active,
taking part in chemical reactions
in and around cells
Usually metabolically
unreactive, with a structural
role
Lipids
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Include fats which tend to be solid at room
temp
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Oils which tend to be liquid
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Produced mainly by animals
Produced mainly by plants
There are many exceptions to this rule
Lipid structure
Made of
carbon,
hydrogen and
oxygen
 Higher
proportion of
hydrogen than
carbohydrates
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Triglycerides
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3 fatty acids attached to a molecule
of glycerol
Fatty acids contain a Carboxyl
group -COOH hence their name
Carboxyl groups of fatty acids are
able to react with –OH (hydroxyl)
groups of glycerol forming ester
bonds
Ester bonds involve covalent bonds
and are very strong
Condensation reaction
Triglycerides
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Insoluble in water
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None of the atoms carry an electrical charge so are not attracted
to water
As they are not attracted to water they are said to be
hydrophobic
Saturated fat- the fatty acids all contain as much
hydrogen as they can. Each carbon atom in the tail is
linked to its neighbouring carbon atom by single bonds,
whilst the other two bonds are linked to hydrogen atoms
Unsaturated fat- one or more fatty acids in which at
least 1 carbon atom is using 2 of its bonds to link to
hydrogen. This double carbon-carbon bond forms a kink
in the chain
Cholesterol
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Cholesterol can be classified as a
lipid.
Not formed the same as triglycerides
and phospholipids
4 carbon-based rings
Found in all biological membranes
Small narrow structure and has a
hydrophobic nature
Cholesterol and other chemicals with
similar structures are called steroids
Cholesterol
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Huge numbers of different kinds of steroids are
found in the body
Steroid hormones- testosterone, oestrogen and
vitamin D
 As
steroids they can pass directly through the
phospholipid bilayer
 Also able to pass through the nuclear envelope (also
made of a lipid bilayer)
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Many cells are able to produce cholesterol as it
is vital to living organisms
Triglycerol
Saturated
Unsaturated
Saturated
Unsaturated
Diagram
Composed of
Any special bonds
Reaction used to join
components
Role in body
Hydrophobic/
Hydrophillic
Phospholipid
Cholesterol
& Steroids
Enzymes