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Biological Molecules
Monomers and Polymers
Monomers – small single units from which layer molecules are made
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Carbohydrates
Monosaccharide -simple sugars, small molecules that dissolve in water
Monosaccharides follow (CH2O) n e
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C6 H12 06
Polysaccharide – large
molecules made of
monosaccharides
Glucose exists in
different forms called
isomers
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Add 2cm3 of food sample in test tube, if its not in liquid form – grind in water
2
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Heat in a water bath, reducing sugars are present it will turn brick red – orange
Using a colourimeter
1
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Set the colourimeter to red and absorbance to 0 using a water blank
3
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They are arranged parallel to one another
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Make sample liquid form
2
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Place in a water bath for 5 minutes
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Add another 2cm3 of the food sample to 2cm3 of dilute hydrochloric acid in a test tube and
place in a water bath
5
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Reheat the sample in the water bath, and it will now turn orange/brown due to reducing
sugars that were produced from hydrolysing non reducing sugars
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Water proofing – lipids are insoluble in water and thus used for water proofing; plant and
animals have waxy cuticles and animals secrete oils

•

Insulation – lipids slow conductors of heat

Properties of lipids
•
•
•
•

Hydrocarbon based
Lower proportion of O relative to C and H than in
carbohydrates
They’re insoluble to water
They are soluble in organic solvents like acetone,
alcohols

Saturated fats are solids at room temp, unsaturated are
liquids due to not being able to pack together because of
double bonds
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Esterification is a condensation
reaction, so water is produced from
it
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Phospholipids
A phospholipid is made of glycerol and two fatty acids
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Fatty acids have no charge and are non-polar = hydrophobic
-

This means it orients itself away from water (but mixes with
fats/triglycerides)

Phosphate group have +ve/-ve charges and are thus polar = hydrophilic
-

Attracted to water, but not fat

Emulsion Test
1
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3
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5
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Protein structures
Primary – polypeptide chain
Secondary – alpha helix or beta pleated sheet
Tertiary – the polypeptide chain in a unique 3D shape caused by bonds between its R groups
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Quaternary – multiple tertiary structures – multi subunits

Test for proteins – Biuret Test
1
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Add a few drops of dilute cooper sulphate solution and mix gently
3
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Enzymes
Enzymes catalyse metabolic reactions
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ES Complexes:

Activation Energy
1
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Energy of the products must be
less than the substrate (so reaction
happens naturally, no energy input
needed)
3
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Two reaction types:
Catabolic – breaks things down
Anabolic – builds things up

Factors affecting enzymes
Denaturing enzymes:
Anything which disrupts the structure will distort the active site, so it no longer functions
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pH change can disrupt or break weak H bonds
and ionic bonds
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2

3

1

1
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Increasing substrate increases rate of reaction
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2
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3
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High
substrate concentration
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2 types: competitive and non-competitive
Competitive inhibition

Inhibitor competes with substrate to fill active site to stop enzyme reacting with substrate
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Non-competitive inhibition
Binds to a site other than the active site of an enzyme
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Such inhibition can be reversible if a
substance can be found for which the inhibition has a greater affinity for than the enzyme
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Competitive line – the curve is this shape as the substrate
concentration increases, the rate of reaction would increase,
just not as fast
...
However, as substrate concentration increases,
the inhibitors are knocked out of the enzyme and substrate
fills the space
...
But as inhibitors
fill the active site, it denatures enzymes, stopping the
reactions from occurring
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The bonds in between nucleotides
connecting phosphate group and pentose
sugar is called a phosphodiester bond
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They are split into pyrimidines and
purines based off size
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The bases each have a pair they bind to
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All base pairs follow Chargaff’s Rule: percentages must be equal
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g
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RNA
Single stranded, ribose has extra OH
group (different pentose sugar), Uracil
replaces Thymine
mRNA
messenger RNA, produced in the nucleus, to then leave
it and act as an instruction for the creation of proteins
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Semi-conservative DNA Replication
1
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DNA helicase breaks the H bonds between
the organic bases in the DNA helix and the
DNA unzips, while SSB proteins hold it
open
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It catalyses condensation

reactions to join adjacent nucleotides,
forming phosphodiester bonds
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4
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Other types of DNA replication theories:

Proof of semi-conservative replication:
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•
•

•

•
•
•

Meselson and Stahl (1958) gave a heavy isotope to E
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All molecules
within the cells containing nitrogen became
heavy
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They then put the cells through density
centrifugation
Cells grown in the N15 media were then
transferred to the N14 media and since E
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They harvested cells every 20
mins, isolated the DNA and density gradient
centrifuged it
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As cells divide furthermore N14 is incorporated into its DNA, resulting in the 2nd generation having
more light strands than heavy
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In the 3rd generation we see a further increase of the light strands to 75% and intermediate to 25%
This allows for evidence to show DNA replication is semi-conservative
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Highly reactive chemical to
link two sorts of reaction
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(exergonic)
Energy given
out

Amino acids
Anabolism
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ATP Hydrolase

ATP Synthase
ATP is hydrolysed and synthases by enzymes
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ATP function and usage:
• ATP remains within cells and can only be sorted for a few minutes, due to instability
• ATP hydrolysis yields 30
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Potassium – important transmission in nerve
impulses
Constantly pumped into cells through active
transport in exchange for sodium
Hydrogen – pH is calculated based on
concentration of hydrogen ions
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Phosphate – used in production of nucleic acids
production of ATP and phospholipids which are
essential in cell membranes

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