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Biological molecules
Water
Water is a simple molecule that can form hydrogen bonds between its molecules
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Hydrogen bonds are weak forces of attraction
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In water there is attraction between the oxygen and the
hydrogen of molecules
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Oxygen attracts electrons more strongly than hydrogen ions
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Therefore, a body of water maintains a fairly
constant temperature, which is essential for aquatic life to survive
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Living thigs can survive below ice
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This energy is known as latent heat
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 Cohesion – the attraction of water molecules produces surface tension, which
creates a habitat on the surface
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 Solvent – as the molecules are polar water can dissolve a wide range of substances
 As a reactant – water molecules are used in a wide range of reactions such as
hydrolysis and photosynthesis
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This means it
can be pressured and pumped in transport systems or used for support in
hydrostatic skeletons
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These are long chains that comprise a number of smaller
molecules called monomers
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They are made up of:
 Five-carbon or pentose sugar
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This is a reaction that releases a water molecule
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This is called hydrolysis

Carbohydrates
Carbohydrates consist of carbon, oxygen and hydrogen
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They
are soluble and sweet reducing sugars
Pentose monosaccharides contain five carbons, e
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ribose and deoxyribose
Hexose sugars contain six carbons, e
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glucose
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Disaccharides
Disaccharides are two monosaccharides bonded together by a glycosidic bond
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Most are reducing sugars, apart from sucrose
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The
most common bond is between the carbon 1 and carbon 4 of two monosaccharides
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Polysaccharides
Polysaccharides are large insoluble molecules
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Amylose – consists of long unbranched chains of alpha glucose subunits
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Amylose is used for the storage of glucose subunits and
energy in plant cells
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It is insoluble, which means the molecules do
not affect the water potential of cells
Amylopectin and Glycogen – are similar to amylose in that they are long chains of alpha
glucose subunits bonded by 1,4 glycosidic bonds
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This means the molecule is branched
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The 1,6 glycosidic bonds make it more branched so it as many ends
that glucose can be released quickly from
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Lipids are insoluble
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The fatty acid chains are joined to the glycerol by a condensation reaction
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Triglyceride molecules are rich in energy and are used to store excess energy
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Water is also released
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If each carbon
has two hydrogen atoms attached, there are no double or triple bonds
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If there are fewer hydrogen atoms, there will be double or even triple
bonds between carbon atoms
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These are found
in plants and oils

Phospholipids
These are similar to triglycerides, but one of the fatty acid chains has been replaced by a
phosphate group
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The
head of the phospholipid is hydrophilic and tail is hydrophobic
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There are 20 different amino acids in
proteins, but all have the same basic structure
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Proteins consist of log, unbranched chains of amino acids, which are held together by
peptide bonds
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A peptide bond is
formed by condensation
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Man amino acids form a polypeptide
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Secondary structure
Formed when the chain of amino acids becomes folded and coiled
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Hydrogen bonds hold the folds and coils in place
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These final folds ad coils are caused by interactions between the R groups on
the amino acids, which form bonds
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Quaternary structure
More than one polypeptide chain (multiple subunits) form the quaternary structure when
they’re folded
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These proteins are more water
soluble
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Their shape and activity are sensitive to temperature
changes as a higher temperature can cause their shape to distort and start to denature
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It is used to transport oxygen
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One haemoglobin molecule can carry four oxygen molecules in the
haem group
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They are less
soluble in water
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