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Chemistry of Life
Atoms: atomic nucleus and electrons that orbit the nucleus
...
Electrons are negatively charged
...

Element: a substance that cannot be broken down not converted into other
substances
Isotopes: same element but different number of neutrons
Radioactive isotopes: nuclei break apart releasing energy
Molecule: consists of 2 or more atoms held together by interactions among electron
shells
Compound: substance made up of different types of atoms
An atom can:
-

Lose electrons (metals) – forms ions

-

Gain electrons (non-metals) – forms ions

-

Share electrons (covalently)

Chemical bonds: forces which hold atoms together in molecules
A bond in which electrons are equally shared – non-polar covalent bond (e
...
C-H)
If one has a larger positive charge and attracts electrons more strongly – polar
covalent bond (e
...
O-H , N-H, C=O)

Water
It forms hydrogen bonds (polar)
...

H2O (l) ↔ H+ (aq) + OH- (aq)
If there are more H+, it is acidic: gives off H+ ions
...
g
...
(E
...
NaOH, -NH2)

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•

Chemical reagent: it participates in chemical reactions (photosynthesis,
condensation and hydrolysis reactions)

•

Solvent:
i)

Dissolves gases: Oxygen will be present even if surface is frozen

ii) For ionic/polar molecules, make it more reactive (hydrophilic)
...

i)

High heat capacity: measure of the amount of heat required to raise the
temp of 1 kg of a substance by 1°C
...


ii) High heat of vaporisation: measure of the heat energy required to convert
a liquid to gas
...

Liquid water must lose a large amount of heat energy to freeze – water in
cells does not freeze easily
...
Ice
insulates the water below it, to ensure survival of aquatic organisms
...

Surface tension is the tendency for the water surface to resist being broken
-

Transpiration tension – cohesion theory: cohesion is pulling up the
chain-like water and adhesion is preventing it from slipping
backwards
...
Fertilisation by motile gametes
2
...
Dispersal and germination of seeds
4
...
Lubrication in joints
6
...
g
...
Protection (Tears, mucus, saliva)
8
...
g
...
Alkanes are saturated whilst alkenes and alkynes are unsaturated
...

Monomers -> polymers
e
...
monosaccharide -> polysaccharide (food storage and structural purposes)
amino acid -> protein
nucleotide -> nucleic acids (info molecules)
NOTE: lipids are made up of glycerol and fatty acids
...


Monomers are joined by condensation; removal of water
Polymers are broken down by hydrolysis; addition of water

Lipids
-

Large regions composed entirely of C and H, with non-polar C-C and C-H

-

Lipids are hydrophobic and insoluble in water but soluble in organic
solvents

Oils, fats and waxes
Contain only C, H and O
...
Fats are solid at RT and oils are liquids
...
g
...
g
...
They are used
for long-term storage (e
...
hibernating bear for food and insulation, aquatic animals
for insulation and buoyancy, known as blubber)
...
g
...

Amphipathic: 2 fatty acid are insoluble but the phosphate – nitrogen is soluble
(found in membranes)





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Glycolipids
They are associations of lipids with carbohydrates
...
With functional groups
...

Involved in reception of light in the eyes
...
Regulates absorption of
Ca2+ in intestine and deposition of Ca in the bones
...



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Carbohydrates


Monosaccharides
Consists of one sugar molecule (CH2O)n, it is soluble in water and they are all
reducing sugars (give brick red precipitate with Benedict’s Test)
They have a backbone of 3-7 Carbons: trioses (3), tetroses (4), pentoses (5), hexoses
(6), heptoses (7)
...
The remaining C is an aldehyde (aldose) or a
keto group (ketose)
...
Glucose can exist in two forms: alpha (makes starch) and
beta (makes cellulose)
...
They
are classified dextro and levo referring to the directions in which solutions of
these compounds rotate the plane of polarising light
...

Functions:
-

Broken down to release energy for cellular activity

-

Linked to form disaccharides and polysaccharides

-

Ribose and deoxyribose imp for DNA and RNA synthesis

-

Ribulose biphosphate made from ribulose and CO2 acceptor in
photosynthesis

-

Triose sugars such as glyceraldehydes and dihydroxycetone are
intermediates in respiration and photosynthesis
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Disaccharides: C x (H 2 O) y
e
...
maltose and lactose (reducing sugars)
2 monosaccharides linked by condensation by a glycosidic bond
•

Maltose: (glucose α – glucose α)

Forms α -1-4- glycosidic bond
-

Occurs in the breakdown of starch by amylase

-

Occurs in germinating seeds
In beer brewing grain is used as starch
...


Disaccharides are used for short- term energy storage
...


Polysaccharides
Many monosaccharides linked by glycosodic bonds
...

Function: structural materials (cellulose and food and energy stores) – starch and
glycogen
...
Made up of:
-

Amylose: straight chain structure coiled helically into a comact
shape (1-4 bonds) – gives blue-black colour with iodine
...


Glycogen: (made from glucose)
Storage in animals and fungi, stored in liver and muscles
...

-

More compact than starch

-

Makes it easier to hydrolyse

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•

Cellulose
-

Unbrached polymer of β-glucose by 1-4- glychosidic bonds
...

They have H bonds forming cross-bridges (binds the chains rigidly
together forming microfibrils (60-70) or macrofibrils (larger) ->
large tensile strength)

-

Fully permeable to water and solutes

-

Broken down by cellulase

Derivative carbohydrates (other elements besides C, H and O)
...
Found in cell wall of fungal hyphae and exoskeleton of
arthropods
...
Important intermediates in respiration and photosynthesis
...
Have –NH2 instead of OH
...


Proteins
Contain C, H, O, N and sometimes S
...


•

Zwitterions
COOH (acidic) and NH2 (basic) therefore they are amphoteric
COOH in water dissociates, releasing H+ ions which can attach to the NH2
giving it a positive charge
...
The N (from NH2) joins the C
(from COOH) by a peptide bond forming dipeptides
...


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Protein structure (3D)
The exact type, position and number of amino acids bearing specific R groups
determine both the structure of the protein and its biological function
...
E
...

haemoglobin has iron, glycoproteins have carbs and lipoproteins have lipids
...


Secondary structure : consists of an α-helix or a β- pleated sheet formed by H
bonds between O (from C=O) and H (in N-H)
-

α-helix: coil where H bonds hold the turns together
...



Tertiary structure
The polypeptide chain folds extensively forming a compact globular 3D shape by
the bonds between different R groups
...
This is
broken by changing the pH of the environment
...
Hydrophilic amino acids form H bonds
with water
...


Proteins can be classified as:
•

Fibrous proteins: secondary structure is the most important, with little or no
tertiary structure
...
g
...


•

Globular proteins: tertiary structure is the most important, form enzymes,
antibodies and hormones (insulin)
...


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•

Immunoglobulins: - 4 polypeptide chains arranged in a Y-shape held
together by disulfide bridges
...


•

Haemoglobin: - contains 4 polypeptide chains of two types (α and β) and 4
haeme groups attached to each polypeptide
...

Replacing a hydrophilic with phydrophobic amin acid can cause sickle-cell
anaemia
...
It unfolds and can no longer perform its
function
...

•

High temperature or radiation: kinetic energy cause the atoms to vibrate,
disrupting H and ionic bonds
...


•

Heavy metals: they form bonds with very charged R groups and disrupt ionic
bonds
...


•

Organic solvents and detergents: disrupt hydrophobic interactions and H
bonds
...


Protein will refold to its original structure if conditions are suitable
...


Nucleic Acids
Long chains of similar but no identical subunits; nucleotides (genetic material)
Nucleotides consist of:
1
...
Phosphate group (from phosphoric acid) which gives acidic character
...
A N-containing base
There are 5 different bases:
-

2 purines: adenine and guanine

-

3 pyramidines: cytosine, thymine and uracil

Sugar + base -> nucleoside + phosphoric acid -> nucleotide
condensation

condensation

2 nucleotides form a dinucleotide by condensation by a phosphodiester bond
...


-

Consists

of

two

polynucleotide

chains

composed

of

deoxyribose

nucleotides in or right-handed helix forming a double helix
...

-

A bonds to T, G bonds to C
...


-

The chains are antiparallel (one strand has its free sugar on one end and
the other has the free sugar on the opposite end)
...
g
...
It is made when some
hormones come in contact with membrane
...

ATPase catalyses reaction when ATP is made from light
...
At the end of the reaction they are
unchanged or regenerated
...
g
...
g
...

e
...
coenzymes: derived from vitamins (e
...
nicotinamide adenine dinucleotide
(NAD+) and ADP+)
coenzyme A: synthesis and oxidation of fatty acids and pyruvate during respiration

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