AP12 Biology
Water
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makes up 50 to 95% of functional living systems
wherever water is present, life exists
compared with other liquids, water is extraordinary
it is covalently bonded
a polar molecule
hydrogen bonding between adjacent water molecules
this makes water behave like a much larger molecule
the consequences of this are
o water has a high surface tension
 allows for cohesion and adhesion
 capillary action moves water up plant stems and in spaces between
cells
o resistance to temperature change due to a high specific heat
 allows earth temperatures to be moderate
 makes ours and other organisms’ body temperatures easier to
regulate
o cooling effect due to high heat of evaporation
 allows sweating to cool us off
o density drops as it freezes (below 4oC)
 ice floats on liquid water and insulates from further freezing
 lakes etc. freeze from top down
o an excellent solvent
 allows blood, cytoplasm to carry dissolved materials
Functions of Elements
Element
Nitrogen
Phosphorous
Potassium
Sulphur
Iron
Function in Plants
amino acids (proteins)
nucleic acids
phospholipids
ATP
activates enzymes
certain amino acids
electron carriers
Function in Animals
amino acids (proteins)
nucleic acids
phospholipids
ATP
activates enzymes
certain amino acids
carries oxygen
AP12 Biology
Carbohydrates
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organic compounds composed of H, C and O
relative proportions are C : 2H : O
they function primarily as energy storage molecules
important structural components in the cell walls of plants
there are three types of carbohydrates
o Monosaccharides – comprised of one simple sugar molecule
o Disaccharides – comprised of 2 simple sugar molecules
o Polysaccharides – comprised of a chain of many simple sugar molecules
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Monosaccharides
o examples are glucose and fructose
o produced during photosynthesis by green plants
o energy of the sun is stored in the bonds of the glucose molecule
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Disaccharides
o formed when 2 monosaccharides are joined together
o occurs through the removal of a water molecule in a reaction called a
condensation reaction or dehydration synthesis
o glycosidic link forms between the monosaccharides
o likewise, in the presence of enzymes water is used when a disaccharides
split into two monosaccharides
o this type of reaction is called hydrolysis
o hydrolysis releases energy while condensation requires energy
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Polysaccharides
o these are long chains of monosaccharides linked together
o produces molecules like starches which are used by plants for energy
storage
o in animals, a polysaccharide called glycogen is used for short term energy
storage
o polysaccharides are hydrolyzed to disaccharides for transport and to
monosaccharides before they can be used in cellular respiration
o other examples of polysaccharides are
 cellulose found in plant cell walls
 chitin found in the exoskeleton of insects
AP12 Biology
Lipids
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lipids are all fatty or oily substances
o non-polar and therefore insoluble in water
o large numbers of H-C bonds and so store large quantities of energy
Fats
o these are lipids stored in the cell and can be made by the cell from sugars
o consist of 3 fatty acid molecules joined to a glycerol molecule
(triglycerides)
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may be either
 saturated
 every C atom in the fatty acid chain (except for the last)
holds 2 H atoms (all that it can)
 usually hard fats like lard
 unsaturated
 some C atoms in the fatty acid chains are joined by double
bonds, and so do not hold all of the H they can
 usually liquid fats like plant oils
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Phospholipids
o composed of 2 fatty acids and a phosphate attached to a glycerol molecule
o the phosphate end of these molecules is polar and therefore water soluble
o the fatty acid end in non-polar and therefore water insoluble
o these molecules thus orient themselves in a very specific way when
exposed to water
o they form cell surface membranes
Waxes
o form protective coverings on feathers, fur, leaves and fruit
Cholesterol
o structurally quite different than other lipids
o not water soluble
o functions:
 cell membranes
 synthesis of certain hormones
AP12 Biology
Proteins
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made of nitrogen containing molecules called amino acids
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there are 20 different amino acids
o amino acids may be polar (water soluble)
 in cell surface membranes are found on the surface or imbedded
between phosphate heads
o non-polar amino acids are not water soluble
 tend to cluster in the center of the polypeptide
 the more non-polar amino acids, the les water soluble the protein
o the polar and non-polar regions arrange themselves so that polar meets polar
and non-polar meets non-polar
essential to cell growth and function
play varied roles in cells
o enzymes
 globular proteins like amylase
o hormones like insulin
o antibodies or immunoglobulins
o structural proteins like collagen in tendons and skin
o cell surface membrane proteins which control the passage of materials
o transport proteins like haemoglobin
usually large molecules with several hundred amino acids in the chain
proteins are formed during a condensation reaction between the amino acids
levels of organization of proteins
o Primary Structure
 this is the linear sequence of amino acids in the protein chain
 the amino acids are joined together head to tail in a linear sequence
dictated by the hereditary information in the nucleus
o Secondary Structure
 the chain will fold in response to the formation of H bonds between
one part of the chain and another
 these folds are the secondary structure
 one common result is the helical shape caused by -bonding
 hair contains this type of protein and so is elastic
 silk contains -bonded chains of amino acids which are straight
chains and pack together very well
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 in collagen (found in cartilage and bone) 3 protein chains wrap around
each other producing a tough fibre
o Tertiary Structure
 sometimes the long helix will fold back on itself due to interaction
between R-groups to produce the tertiary structure
 examples are enzymes and antibodies
o Quarternary Structure
 2 or more globular proteins fit together
 produces a complex shape
 an example is hemoglobin
Globular proteins
o compact and almost spherical
o most are lipid soluble
 primary to quarternary structure
Fibrous proteins
 built up from a single repetitive structure
 provide mechanical support for cells
 can be helices or pleated sheets
 collagen in skin and bones
 elastin in skin and blood vessels