Answer: Hemoglobin has 4 tertiary structure protein
chains which enable them to perform the function of transporting
oxygen around the body.
Introduction: The oxygen taken in by the mammals during
respiration needs to be transported from lungs to different parts
of the body. This transport is done by a protein called hemoglobin,
present in the RBCs of the blood.
Different levels of polypeptide structures:
- Primary structure: Amino acids join together to form a
polypeptide chain in a specific order by forming peptide bonds.
This reaction is called condensation reaction in which water
molecule is released.
- Secondary structure: These polypeptide chains do not remain in
a straight line. They bend to form a 3-D shape either an alpha
helix (spiral) or a beta sheet (accordion shape). These secondary
structures are held together by hydrogen bonds
- Tertiary structure: This is the final form of the protein and
is functional. The tertiary structure is formed by secondary
structure components. The hydrophobic regions are to the interior
and the hydrophilic regions are to the exterior
- Quaternary structure: Some complex proteins possess this
structure. The protein consists of multiple chains with multiple
- The quaternary protein structure consists of 4 tertiary
polypeptide chains which are all alpha helices
- Each alpha helix is a seconadry polypeptide structure made of
- The sequence amino acids in turn are the primary structure of
- The 4 secondary structure chains or alpha helices surround the
iron molecule which is called a heme group
- The oxygen binds to this heme group. There are 4 heme sites for
the oxygen binding in hemoglobin
- Structural changes occur as oxygen binds to it. First oxygen
binding is difficult but the other 3 oxygen molecules bind easily.
Changes continue to occur in the hemoglobin sub units
- Oxygen levels in the blood decrease as the carbon dioxide
levels increase. And oxygen is released and the shape of the
hemoglobin changes again
- All four oxygen molecules are released eventually
Conclusion: Thus, there is a clear relationship between
the different levels of organization of hemoglobin polypetide and