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biological molecules
subtopic
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1 Monomers and polymers
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2 Carbohydrates
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3 Lipids
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2 Many proteins are enzymes
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2 DNA Replication
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6 ATP
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7 Water
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8 Inorganic Ions

learnt

RAG

Most carbohydrates are polymers;
Polymers are large, complex molecules composed of monomer subunits joined
together
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g
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g
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g
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These control what enters and
leaves the cell
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the hydrophobic tails and hydrophilic heads mean that they create a bilayer
the centre of this bilayer is hydrophobic, meaning water-soluble substances can’t
easily pass through

emulsion test
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shake test substance with ethanol so that substance dissolves
pour into water
if a lipid is present, a milky emulsion will form
o the more lipid, the more concentrated

amino acids
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all amino acids have the same general
structure
the NH2 amino group
the COOH carboxyl group
the ‘R group’ variable region
there are 20 amino acids which all living
things share

Dipeptides and polypeptides are formed in a condensation reaction with two or more
amino acids
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This occurs with the -OH on
the carboxyl group and an H on the amino group
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enzymes & their tertiary structure
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enzymes have a very specific shape
o only catalyse one reaction
o as only one complementary substrate will fit
shape is determined by the protein’s tertiary structure
o which is determined from its primary structure
each enzyme has a different tertiary structure therefore a different shape of active
site – if the active site and substrate aren’t complementary, enzyme-substrate
complexes won’t be formed
if the tertiary structure is altered in any way, it will not catalyse the reaction
o this can be altered by genetic mutations (which would change the primary
structure), pH or temperature

temperature’s effect on enzyme activity
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up to a certain temperature, an increase of temperature will result in an increase of
rate of reaction (ROR)
o this is because the substrate and enzyme have more kinetic energy
o this means they’ll be more likely to collide and form enzyme-substrate
complexes
however, over a certain temperature, the increased
kinetic energy will break the bonds in the enzyme
o this means the active site changes shape
o no more e-s complexes can be formed
o the enzyme is denatured

pH’s effect on enzyme activity
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above and below optimum pH, the OH- and the H+
ions found in alkalis and acids respectively can
change ionic and hydrogen bonds in the enzymes
tertiary structure
active site changes shape
enzyme denatured

enzyme concentration effect on rate of reaction
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the more enzyme molecules in a solution, the
more likely a substrate is to collide with it
this would mean more e-s complexes, and speed
up ROR
however, is substrate is limited, adding more
enzymes will have no further effect

substrate concentration effects on rate of reaction
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the more substrate molecules, the more likely it is
to collide with an enzyme
this means more e-s complexes, and speed up ROR
however, there will be a point when all enzyme
active sites are saturated
at this point, adding more substrate will not speed
up rate of reaction

enzyme inhibition
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competitive inhibitors
o have similar shape to substrate molecules
o compete with substrate to bind to active
site (no reaction takes place)
o they block the active site so substrate
cannot fit into it
o if there is a high concentration of
inhibitor, it will take up many active sites
o of there is a higher concentration of
substrate, the chances of the substrate
getting into an active site is increased, therefore increasing ROR

•

non-competitive inhibitors
o non-competitive inhibitor molecules bind
to the enzyme away from its active site
o therefore, the active site changes shape
o substrate can no longer bind to the enzyme
o increasing substrate concentration will not
make any difference to ROR

structure of nucleotides
• DNA and RNA have a pentose sugar
• nitrogen containing organic base
• phosphate group

structure of DNA nucleotide
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the pentose sugar in DNA is deoxyribose
there are 4 bases that the nitrogenous base could be
o adenine, guanine, cytosine or thymine

structure of RNA nucleotide
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pentose sugar in RNA is ribose
there are 4 bases
o they’re the same in DNA, but uracil replaces thymine

polynucleotides
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polymer of nucleotides
nucleotides join via a condensation reaction
between phosphate group and pentose sugar
forms a phosphodiester bond
forms a sugar-phosphate backbone (in DNA it is
a deoxyribose-phosphate backbone, in RNA it is
a ribose-phosphate backbone)

DNA structure
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two DNA polynucleotides are joined by hydrogen bonds at the nitrogenous bases
A bonds to T, G bonds to C
o this is specific base pairing
o there are 3 hydrogen bonds between G and C
o there are 2 hydrogen bonds between A and T
the polynucleotide chains are antiparallel
they form a DNA double-helix

RNA structure
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made of single polynucleotide chain
short in comparison to DNA

DNA replication
DNA replication is semi-conservative as half of the stands in each new DNA molecule are
from the original DNA molecule; there is a genetic continuity between generations
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the active site of DNA polymerase is only
complementary to the 3’ to 5’ end
can only add nucleotides to the new strand
at the 3’ end
the new strand is made in a 5’ to 3’
direction
the DNA polymerase working on one of the
template strands moves in the opposite
direction to the DNA polymerase working
on the other template strand

water as a metabolite
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many metabolic reactions involve condensation or hydrolysis reactions
hydrolysis reactions require a molecule of water to break a bond
condensation reactions release a molecule of water in the formation of a bond
o e
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amino acids joined together to form polypeptides via a condensation
reaction
o energy is released from ATP via a hydrolysis reaction

water’s high latent heat of vaporisation
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takes a lot of energy to break the H-bonds between water molecules
therefore, water has a high latent heat of vaporisation
o this means a lot of energy is used when water evaporates
useful to cool down organisms
o e
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humans sweat

water’s high specific heat capacity
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the H-bonds between a water molecule absorb lots of energy
therefore, water has a high specific heat capacity
this is good in organisms as water does not undergo rapid changes in temperature
o makes areas around water a good habitat
o maintains internal body temperature

water’s polarity
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water’s polarity makes it a good solvent for ionic substances
o e
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salt
ion gets totally surrounded by water molecules due to the ionic charge and water’s
polarity
therefore, water is a good solvent
moreover, water’s polarity means that it is very cohesive
this makes water flow, and is therefore good in transporting substances
o e
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helps water travel in columns up a xylem in plants
also means that it has strong surface tension
o means that sweat forms droplets
o and why pond skaters and other insects can “walk” on water

ATP
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the energy released from glucose is used to make ATP
it is made from the nucleotide
base adenine, a ribose sugar, and
three phosphate groups
it is nucleotide derivative
once made, ATP diffuses to the
part of the cell where energy is
required
the energy in the phosphate bond
is high, therefore when hydrolysed, releases energy

ATP usage
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when energy is needed, ATP is hydrolysed to form ADP and Pi
this is catalysed by the enzyme ATP hydrolase
ATP hydrolysis can be coupled to other energy-requiring reactions in the cell
o energy released can be used directly to make the coupled reaction happen,
rather than being wasted as heat
the inorganic phosphate molecule released can be added to another compound in a
process called phosphorylation, which often makes a compound more reactive

inorganic ions
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iron ions in haemoglobin
o haemoglobin is made of 4 polypeptide chains and an Fe2+ in the centre
o this binds to the oxygen
o when bound to oxygen, it temporarily becomes Fe3+
hydrogen ions determining pH
o pH is determined by the concentration og H+ ions
o the more hydrogen ions present, the more acidic a solution
sodium ions in co-transport
o glucose and amino acids need help crossing cell membranes
o a molecule of glucose or an amino acid can be transported into a cell
alongside Na+ ions via co transport
phosphate ions in ATP and DNA
o DNA, RNA and ATP all contain phosphate groups (PO43-)
o the bonds between phosphate groups store the energy in ATP
o phosphate groups in DNA and RNA allow nucleotides to join and form
polynucleotides



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