Presentation1

Chelating Agents
• Porphyrins are complexes

containing a form of the
porphine molecule
shown at the right.
• Important biomolecules
like heme and chlorophyll
are porphyrins.
Red blood cells specialisations
1) biconcave shape 2) no nucleus
 extra space inside
3) contain
haemoglobin
 the oxygen
increases the surface carrying molecule
area so more oxygen
can be carried
Facts About Hemoglobin
Hemoglobin is found in the red blood cells of the body.
Each red blood cell (RBC) contains approximately 280 million hemoglobin
molecules.
The main function of hemoglobin is to transport oxygen from the lungs to

the tissues and then transport CO2 back from the tissues to the lungs.
One hemoglobin molecule has the ability to transport up to 4 oxygen

molecules.
There are two forms of hemoglobin:
(A)Oxyhemoglobin, which is saturated with oxygen molecules

(B)Deoxyhemoglobin, which is desaturated with oxygen molecules
Oxyhemoglobin has a higher affinity for oxygen than deoxyhemoglobin, and
deoxyhemoglobin has a higher affinity for CO2 than oxyhemoglobin.
Therefore, oxygen binds to oxyhemoglobin in the lungs and is then

transported through the blood stream until it reaches the tissues.
There, the oxygen is released to myoglobin, which then transports it to the

mitochondria where it is used for aerobic respiration.
In exchange, the deoxyhemoglobin picks up 2 protons and 2 molecules of

CO2 and returns to the lungs, where the CO2 is released through
exhalation.
Structure of Hemoglobin
Hemoglobin is a tetramer composed of 4 globin molecules; 2 alpha globins

and 2 beta globins.
The alpha globin chain is composed of 141 amino acids and the beta globin
chain is composed of 146 amino acids.
Each globin chain also contains one heme molecule.
The heme molecule is composed of a porphyrin ring, which contains 4

pyrrole molecules cyclically linked together, and an iron ion ligand bound in
the center.
The alpha and beta subunits of the globin chains exist in two dimers which
are bonded together strongly
Each of the 4 globin chains is represented in a
different color. The heme molecule is shown in
red.
Heme molecule. Porphorin ring with iron atom ligand bound
inside.
Oxygen binds to the iron ion tightly.
If two heme molecules come together in the presence of oxygen the iron
atoms will oxidize and irreversibly bind to the oxygen.
This irreversible binding would not be of use in the hemoglobin molecule

because oxygen needs to be released in the tissues.
The globin chain prevents this irreversible binding by folding the protein
around the heme molecule, creating a pocket to isolate the heme molecule
from other heme molecules.
Therefore, the globin molecules allow the iron atom to form loose bonds with
the oxygen, and therefore, the ability to bind to oxygen and then release it into
the tissues without becoming permanently oxidized in the process.
Function of Hemoglobin
The ability of hemoglobin to take up oxygen molecules in the lungs and then release
them in the tissues is regulated by several factors both within the hemoglobin
molecule itself and through external chemical factors.
One of the biggest regulators of the oxygen affinity of the hemoglobin is the
presence of oxygen itself.
In the lungs where the oxygen levels are high, the hemoglobin has a higher affinity
for oxygen and this affinity increases disproportionately with the number of
molecules it already has bound to it.
In other words, after the oxyhemoglobin binds one molecule of oxygen its affinity for
oxygen increases until the hemoglobin is fully saturated.
In the same way, the deoxyhemoglobin has a lower affinity for oxygen and this
affinity decreases disproportionately with the number of molecules it already has
bound.
Thus, the loss of one oxygen molecule from the deoxyhemoglobin lowers the affinity
for the remaining oxygen.
Function of Haemoglobin
When there is a high concentration of oxygen e.g in the alveoli

haemoglobin combines with oxygen to form oxyhaemoglobin. When the
blood reaches the tissue which have a low concentration of oxygen the
haemoglobin dissociates with the oxygen and the oxygen is released into
body tissues
Dr. Harminder Singh

Dr. Harminder Singh
This regulation is known as cooperativity and is essential to the functioning of the
hemoglobin because it allows the oxyhemoglobin to carry the maximum amount of
oxygen to the tissues and then allows the deoxyhemoglobin to release the maximum
amount of oxygen into the tissues.
Cooperativity is a function of the hemoglobin's unique structural characteristics.
Essentially, hemoglobin is an allosetric protein that has more than one shape and can undergo conformational
changes in its structure based on environment conditions.
There are two alternative structures of hemoglobin; the relaxed structure (R) which has a greater oxygen
affinity, and the tense structure (T) which has lower affinity for oxygen.
The change between the T and R structures is the result of a rotation of 15 degrees between the two alpha-
beta dimers (Keates, 2004).
In the T structure, the iron ion is pulled out of the plane of the porphyrin ring and
becomes less accessible for oxygen to bind to it, thus reducing its affinity to oxygen.
In the R structure the iron atom is in the plane of the porphyrin ring and is accessible
to bind oxygen, thus increasing its oxygen affinity.
The transformation from the T to R structure occurs when oxygen binds to the T
structure under the high oxygen pressure environment in the lungs, which causes
the rotation of the two dimers and shifts the remain iron atoms so that they become
more accessible to oxygen.
Likewise, the transformation from the R to T structure occurs when oxygen is

released under the low oxygen pressure environment of the tissues which causes
the dimers to rotate back and shifts the iron atoms so that they become less
accessible to oxygen.
Thus, the cooperativity of the hemoglobin molecule can be explained by its unique
structure which allows it to shift between the T and R structures in the presence or
absence of oxygen.
Chemistry In Action
Dr. Harminder Singh Dr. Harminder Singh

Chlorophyll as a Photoreceptor
It is found in the chloroplasts of green plants, and is what makes green plants,
green.
The basic structure of a chlorophyll molecule is a porphyrin ring, co-ordinated to a

central atom. This is very similar in structure to the heme group found in
hemoglobin, except that in heme the central atom is iron, whereas in chlorophyll it
is magnesium.
There are actually 2 main types of chlorophyll, named a and b.
They differ only slightly, in the composition of a sidechain (in a it is -CH3, in b it is

CHO).
Both of these two chlorophylls are very effective photoreceptors because they
contain a network of alternating single and double bonds, and the orbitals can
delocalise stabilising the structure. Such delocalised polyenes have very strong
absorption bands in the visible regions of the spectrum, allowing the plant to
absorb the energy from sunlight.
The different sidegroups in the 2 chlorophylls 'tune' the absorption spectrum
to slightly different wavelengths, so that light that is not significantly absorbed
by chlorophyll a, at, say, 460nm, will instead be captured by chlorophyll b,
which absorbs strongly at that wavelength.
Thus these two kinds of chlorophyll complement each other in absorbing

sunlight.
Plants can obtain all their energy requirements from the blue and red parts of
the spectrum, however, there is still a large spectral region, between 500-
600nm, where very little light is absorbed.
This light is in the green region of the spectrum, and since it is reflected, this
is the reason plants appear green.
The chlorophyll molecule decays in the autumn and the woodlands turn red,
orange, and golden brown. Chlorophyll can also be damaged when
vegetation is cooked, since the central Mg atom is replaced by hydrogen
ions.
This affects the energy levels within the molecule, causing its absorbance
spectrum to alter. Thus cooked leaves change colour - often becoming a
paler, insipid yellowy green.

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Chelating Agents

• Porphyrins are complexes

The main function of hemoglobin is to transport oxygen from the lungs to

One hemoglobin molecule has the ability to transport up to 4 oxygen

There are two forms of hemoglobin:

(A)Oxyhemoglobin, which is saturated with oxygen molecules

Therefore, oxygen binds to oxyhemoglobin in the lungs and is then

There, the oxygen is released to myoglobin, which then transports it to the

In exchange, the deoxyhemoglobin picks up 2 protons and 2 molecules of

Hemoglobin is a tetramer composed of 4 globin molecules; 2 alpha globins

Each globin chain also contains one heme molecule.

The heme molecule is composed of a porphyrin ring, which contains 4

This irreversible binding would not be of use in the hemoglobin molecule

When there is a high concentration of oxygen e.g in the alveoli

Dr. Harminder Singh

Cooperativity is a function of the hemoglobin's unique structural characteristics.

Likewise, the transformation from the R to T structure occurs when oxygen is

Dr. Harminder Singh Dr. Harminder Singh

The basic structure of a chlorophyll molecule is a porphyrin ring, co-ordinated to a

They differ only slightly, in the composition of a sidechain (in a it is -CH3, in b it is

Thus these two kinds of chlorophyll complement each other in absorbing

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