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Haemoglobin and Collagen
Haemoglobin is an example on a globular protein, a protein that appears to curl up into a ball. It is a
pigment which is found in red blood cells and carries oxygen. Haemoglobin has four polypeptide
chains, two and two . Each of these chains winds itself around a group of atoms with an iron ion in
the centre and these groups of atoms are called a haem group.
This haem group is essential for the functioning of the haemoglobin molecule in the transportation of
oxygen as the iron ion in each of the four haem groups in a haemoglobin molecule is able to bond
with two oxygen atoms, meaning that each haemoglobin molecule is able to carry eight oxygen
Sickle Cell Anaemia
A person with sickle cell anaemia has red blood cells that can go seriously out of shape when oxygen
levels in the blood are low. The cells form sickle shapes rather that their usual biconcave disc shape.
They are then unable to carry oxygen and get stuck in capillaries, leading to damage to tissues.
It is caused by a difference in the primary structure of the polypeptide in haemoglobin. Just one
amino acid is different. Where there should be the amino acid glutamate, there is valine. Glutamate
has a small charge on it, which makes it associate with water molecules, which enable haemoglobin to
be soluble in water. But valine has no charge and so decreases the solubility of haemoglobin. Also
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Collagen is a fibrous protein, meaning that it is structured as long strands. It is found in skin, tendons,
bones, teeth, cartilage and the walls of blood vessels and is an important structural protein. It
consists of three polypeptide chains, each in the shape of a helix, wound together to form a `rope',
meaning that it is strong. Almost every third amino acid in each polypeptide is glycine which is the
smallest amino acid.…read more