Haemoglobin Essay (Unit 2)

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TJ Essay on haemoglobin
Haemoglobin: An Essay
What is it?
Haemoglobin is a globular protein molecule made up of four polypeptide chains coiled into
a helix shape. There are two beta pleated sheets (146 amino acids long) and two alpha
helices (141 amino acids long). Each chain folds in on itself and the four chains are linked
together, forming a round globular shapes molecule (each chain folds in on itself to form a
singular globin molecule). Each polypeptide chain has its own haem group, consisting of a
ferrous (Fe2+ ion) iron molecules, which can combine to a single molecule of O2, as there are
4 polypeptide chains and therefore each haemoglobin molecule can carry 4 molecules of O2
when fully saturated. As haemoglobin contains metal ions and proteins it is often referred
to as a metalloprotein. Similar haemoglobin molecules can be found in all mammals and
most vertebrates, and even some invertebrate organisms such as lug worms. Amino acids
in an organisms DNA code for specific polypeptides that result in the structure of
haemoglobin, these amino acids sequences
vary from organism to organism resulting in
different type of haemoglobin depending on
the organism it comes from.
(left b)The chemical structure of a haem group, with the Fe ion in the centre and (right a) is
a diagram representation of a haemoglobin molecule.
What is it used for?
Haemoglobin transports oxygen around the body. In order to do so efficiently it must bind
to O2 molecules easily (also known as associating or loading) to be able to transport them
but also release the O2 molecules readily (also called disassociating or unloading) so that
respiring tissue can use it. In order to this Haemoglobin molecules bind to O2 molecules
less readily (dissociate) in the presence of CO2, as when the gas is dissolved in the blood it
becomes acidic, lowering the PH and resulting in the haemoglobin molecule to change
shape and disassociate with the O2 molecules readily. High levels of CO2 are found in

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TJ Essay on haemoglobin
respiring tissue as it is a by-product of respiration. Since HB has a lower affinity around CO2
oxygen will readily be released in order for cell tissue to respire further. A high O2
concentration and a low CO2 concentration (such as the ones found at gas exchange
surfaces) results in haemoglobin associating more readily with O2.…read more

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TJ Essay on haemoglobin
Variations in haemoglobin
As mentioned before different amino acid sequences in mammals allow for variation in their
individual HB molecules ability to associate and dissociate with O2 molecules. Environmental factors
have affected how organisms have adapted their haemoglobin molecules in order to be the most
efficient despite their environment.
Animals that have haemoglobin with a high affinity for oxygen take up oxygen but release it
less readily and low affinity haemoglobin takes it up less readily but releases it easily.…read more


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