A
chemical can also be identified by its retardation factor (Rf)
 The formula is:
Rf = distance moved by sample
distance moved by solvent
The answer is never greater than 1.
Glycine = 0.26
Leucine = 0.73
Proline = 0.43
Serine = 0.27
Tryptophan = 0.66
Mixture:
Glycine, Leucine and
tryptophan
Grab a whiteboard and pen
For enzymes to have their effect, the active site and substrate have
to physically meet, and the active site must be able to ‘fit’ or
contain the substrate.
Which factors could affect the rate of enzyme controlled
reactions?
pH
Temperature
Enzyme
cofactors
concentration
Substrate
concentration
Inhibitors
Can you explain what this graph shows in
terms of substrate/enzyme interaction?
Increase in temperature gives molecules
greater kinetic energy and they move
around more quickly increasing the chance
of molecules colliding. This causes an
enzyme controlled reaction to increase its
rate of reaction.
Above this temperature the increasing vibration of the
molecules cause the hydrogen bonds to break and
cause a change in the tertiary structure of the
enzyme. This alters the active site of the enzyme.
The enzyme is then said to be DENATURED. This
is a permanent change in the structure .
pH refers to the concentration of H+ ions in a solution. These hydrogen ions (or
hydroxyl ions) can interact with charged side chains of amino acids, and interrupt
hydrogen bonds within the protein structure. This can have an effect on the shape
of the active site of the enzyme.
The rate of an enzyme catalysed reaction will vary with changes in
pH. Enzymes have a narrow optimum range and small changes in
pH can affect the rate of reaction without affecting the structure of
the enzyme.
At extremes of pH, the
hydrogen bonding is
affected and the 3D shape
of the enzyme is altered and
so is the shape of the active
site.
What would a rate of enzyme controlled reaction look like with
increasing substrate concentration?
If the amount of enzyme is constant, the
rate of reaction will increase as the
substrate increases, as more interactions
can happen between the substrate and
active site of the enzyme.
But there must come a point when all
the enzyme’s active sites are working to
full capacity i.e. all the active sites are
filled.
Vmax
If there is an excess of substrate, the greater the concentration
of enzymes, the quicker the rate of reaction. This is because
there are more active sites available to catalyse the reaction.
However if there is a limited supply of substrate, increasing
the enzyme concentration will not further increase the rate of
reaction, as there are already enough active sites to
accommodate the available substrate molecules.
These devices are made up of a transducer and a biological
element that may be an enzyme, an antibody or a nucleic acid.
The ‘bioelement’ interacts with the sample being tested and
the biological response is converted into an electrical signal by
the transducer.
 a)
3 marks max
 Enzyme/active site has a (specific) tertiary
structure 
 Only glucose has the correct shape/ is
complementary/ will fit 
 To active site 
 (Forming) enzyme-substrate complex 
 DO NOT allow ‘same’ shape! 
 DO NOT allow active site is on the substrate 
 b)
2 marks max
 (Only detects glucose whereas) Benedict’s
detects (all) reducing sugars/ example(s) 
 Provides a reading/ is quantitative/ Benedict’s
only gives a colour/ doesn’t measure
concentration/ is qualitative/semiquantitative 
 Is more sensitive/ detects low concentration 
 Red colour/ colour of blood masks result 
 Can monitor blood glucose conc. Continuously
 DO NOT credit ‘quicker’/ ‘more accurate’