Chemicals of life
1
‘Organisms’
are made from
‘Organic matters’
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2
The Macromolecules of cells
The Unique Water molecule
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4
The water molecule is not
linear
V-shaped
linear
5
Polarity and hydrogen bond
6
Polarity and hydrogen bond
7
Polarity and hydrogen bond
8
Result of regular arrangement of
water molecules: ice crystals
9
Peculiar Properties of water
1. Universal Solvent
2. High heat capacity, heat of
fusion, heat of vaporizaton
3. Density & Freezing
properties
4. Surface tension
A waterstrider / pond skater demonstrates how cohesion
(H-bonds) between water molecules allow it to move
across water's surface.
10
11
Water- an universal solvent
----- for polar and charged particles
Water and oil are immiscible.
“like dissolves like”
oil (long hydrocarbon chain, non-polar)
Vs
water (polar, H-bonding)
13
Fatty substances form membrane
compartments in cells to allow
different reactions to take place
independently of one another
14
High heat capacity, high heat
of vaporization and fusion
15
High heat capacity, high
heat of vaporization and
fusion
16
high heat of vaporization
17
18
Cohesion in water molecule
19
Cohesion and surface tension
20
Cohesion and water transport
in plants
21
Ice is less dense than water
22
23
What would happen to life in the
lake when the lake is frozen?
24
Water as a reactant
photosynthesis
digestion
25
Turgor and wilting
 Turgor loss in plants causes wilting
 Which can be reversed when the plant is
watered
Water- the habitat for many life
forms
27
Minerals in DNA – P, N,
28
Minerals in functional molecules –
haemoglobin, chlorophyll
29
Minerals : Iron containing haem
in haemoglobin holds oxygen
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Minerals - calcium
31
Minerals- nerve activities:
ions movements _ Na+, K+
32
Carbohydrates
Monosaccharides with different no. of Carbon
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Common Monosaccharides
Six-carbon sugars
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Linear and Ring forms
35
Alpha and beta form of
glucose
36
Interconversion of Mono-- Di-polysaccharides
37
Condensation / dehydration
synthesis
38
Disaccharides
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Reducing and non-reducing
sugars
40
Test for reducing sugars
41
Sugars are sweet! How sweet is
it?
Sugar
Relative sweetness
to sucrose
lactose
0.16
galactose
0.32
maltose
0.33
sucrose
1.0
fructose
1.73
aspartame
180
saccharin
450
42
Polysaccharide-starch
43
helical structure of starch
44
Starch grains in plant cells
45
Glycogen: an animal polysaccharide
Mitochondria Glycogen granules
0.5 µm
Glycogen
Cellulose- a structural material
47
LE 5-7
a Glucose
b Glucose
a and b glucose ring structures
Starch: 1–4 linkage of a glucose monomers.
Cellulose: 1–4 linkage of b glucose monomers.
•
•
•
Polymers with alpha glucose are helical
Polymers with beta glucose are straight
In straight structures, H atoms on one strand can
bond with OH groups on other strands
• Parallel cellulose molecules held together this way
are grouped into microfibrils, which form strong
building materials for plants
LE 5-8
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
0.5 µm
Plant cells
Cellulose
molecules
b Glucose
monomer
 Enzymes that digest starch by hydrolyzing alpha
linkages can’t hydrolyze beta linkages in cellulose
 Cellulose in human food passes undigested through
the digestive tract as insoluble fiber
 Some microbes use enzymes to digest cellulose
 Many herbivores, from cows to termites, have
symbiotic relationships with these microbes
 Chitin, another structural polysaccharide, is
found in the exoskeleton of arthropods e.g
insects
 Chitin also provides structural support for the cell
walls of many fungi
 Chitin can be used as surgical thread
Obesity
55
What are Lipids?
 The unifying feature of lipids is having little or no
affinity for water
 Lipids are hydrophobic -- because they consist mostly of hydrocarbons, which
form nonpolar covalent bonds
 The most biologically important lipids are fats,
phospholipids, and steroids
56
LE 5-11a
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
A Triglyceride
58
 Fats made from saturated fatty acids are called
saturated fats
 Most animal fats are saturated
 Saturated fats are solid at room temperature
 A diet rich in saturated fats may contribute to
cardiovascular disease through plaque deposits
LE 5-12a
Stearic acid
Saturated fat and fatty acid.
Saturated and unsaturated fats
61
 Fats made from unsaturated fatty acids are
called unsaturated fats
 Plant fats and fish fats are usually unsaturated
 Plant fats and fish fats are liquid at room
temperature and are called oils
LE 5-12b
Oleic acid
double bond
causes bending
Unsaturated fat and fatty acid.
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Phospholipid
-replacing a fatty acid
(nonpolar) with a
phosphate (polar)
65
Phospholipids-
lipids with a polar head
66
Lipid bilayer
67
Lipid bilayer forms membrane
STEROIDS
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 The basic structure of testosterone (male
hormone;睪固酮) and estradiol (female hormone;
雌激素) is identical.
 Both are steroids with four fused carbon rings, but they differ in the
functional groups attached to the rings.
 These then interact with different targets in the body.
Steroid tree
71
Proteins have many structures,
resulting in a wide range of
functions
 Proteins account for more than 50% of the dry
mass of most cells
 Protein functions include
support,
storage,
transport,
cellular communications,
movement,
body defense
Amino acids – general formula
Variable properties according
to the
R group
75
Amino acids - examples
76
Peptide bond - dipeptide
77
Amino Acid Polymers
 Amino acids are linked by peptide bonds
 A polypeptide is a polymer of amino acids
 Polypeptides range in length from a few
monomers to more than a thousand
 Each polypeptide has a unique linear sequence
of amino acids
Polypeptides
 Polypeptides are polymers of amino acids
 A protein consists of one or more polypeptides
Protein Conformation and
Function
 A functional protein consists of one or more
polypeptides folded, and coiled into a unique
shape
 The sequence of amino acids determines a
protein’s three-dimensional conformation
 A protein’s conformation determines its
function
Groove
A ribbon model
Groove
A space-filling model
Four Levels of Protein
Structure
 The primary structure of a protein is its unique
sequence of amino acids
 Secondary structure, found in most proteins, consists
of coils and folds in the polypeptide chain
 Tertiary structure is determined by interactions among
various side chains (R groups)
 Quaternary structure results when a protein consists
of multiple polypeptide chains
 Primary structure, the sequence of amino acids in
a protein, is like the order of letters in a long word
 Primary structure is determined by inherited
genetic information
 Typical secondary structures are a coil called a helix
and a folded sheet structure
Amino acid
subunits
b pleated sheet
 helix
 Tertiary structure is determined by interactions
between R groups, rather than interactions between
backbone constituents
 These interactions between R groups include
hydrogen bonds, ionic bonds, hydrophobic
interactions, and van der Waals interactions
 Strong covalent bonds called disulfide bridges may
reinforce the protein’s conformation
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond
 Quaternary structure results when two or more
polypeptide chains form one macromolecule
 Collagen is a fibrous protein consisting of three
polypeptides coiled like a rope
 Hemoglobin is a globular protein consisting of
four polypeptides: two alpha and two beta chains
Polypeptide
chain
b Chains
Iron
Heme
Polypeptide chain
Collagen
 Chains
Hemoglobin
Sickle-Cell Disease: A Simple
Change in Primary Structure
 A slight change in primary structure can affect a
protein’s conformation and ability to function
 Sickle-cell disease, an inherited blood disorder,
results from a single amino acid substitution in
the protein hemoglobin
LE 5-21a
10 µm
Red blood Normal cells are
cell shape full of individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Red blood
cell shape
Fibers of abnormal
hemoglobin deform
cell into sickle
shape.
LE 5-21b
Sickle-cell hemoglobin
Normal hemoglobin
Primary
structure
Val
His
1
2
Leu
Thr
3
4
Pro
Glu
5
6
Secondary
and tertiary
structures
7
b subunit
Quaternary Normal
hemoglobin
structure
(top view)
Primary
structure
Secondary
and tertiary
structures
Molecules do
not associate
with one
another; each
carries oxygen.
His
Leu
Thr
Pro
Val
Glu
1
2
3
4
5
6
7
Exposed
hydrophobic
region
b subunit

Quaternary
structure
b
Val
b

Function
Glu
Sickle-cell
hemoglobin
b

Function
Molecules
interact with
one another to
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
b

What Determines Protein
Conformation?
 In addition to primary structure, physical and
chemical conditions can affect conformation
 Alternations in pH, salt concentration,
temperature, or other environmental factors can
cause a protein to unravel
 This loss of a protein’s native conformation is
called denaturation
 A denatured protein is biologically inactive
Protein – internal Forces/ bonding
93
LE 5-22
Denaturation
Normal protein
Denatured protein
Renaturation
Protein – What level of protein
structure is represented below?
95
Protein – Levels of complexity
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Protein –
globular proteins
proteins with physiological function
97
Globular protein e.g. enzyme
Protein – globular proteins: e.g.
antibodies
99
Structural proteins
Protein –
Fibrous proteins with structural
function e.g. collagen
101