Haemoglobin
haemoglobin, protein structure,
polypeptide, oxygen, carbon dioxide,
affinity, association, dissociation.
Learning outcomes
• Describe the structure of haemoglobin using
knowledge of protein structure D
• Explain the role of Hb in the transport of
oxygen C
• Explain the properties required by Hb in the
transport of oxygen C
• Sketch oxygen dissociation curves and explain
their features B
Protein structure
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Primary structure- sequence of
amino acids joined by covalent
bonds between carboxyl and amino
groups.
Secondary structure- the way the
protein folds as a result of Hbonding. Can have α-helices or βpleated sheets.
Tertiary structure- the way the
folded pp folds again to form a 3D
shape. This is held in place by H
bonds, disulphide bridges and ionic
bonds. It is at this stage a protein
can become conjugated with a nonprotein molecule called a
prosthetic group.
Quaternary structure- when two or
more pp join together to form an
active protein.
Haemoglobin
• Which level of
structure is it & why?
• What does Hb have
to do?
• What are the
properties of Hb as
an oxygen carrier?
Haemoglobin structure
What can you tell about
this protein structure?
• Primary structure of 4
polypetide chains called
globin
• Secondary structure which
coils the 4 pp into α helices
• Tertiary structure which
folds each chain into its 3D
shape
• Quaternary structure links
the 4 pp into an almost
spherical structure. Each
chain is associated with a
haem group (Fe2+) which can
carry an O2 molecule.
How does it work
• Each haem molecule can carry an O2 molecule
So Hb + 4O2
HbO8
• In the lungs there is a raised pH as there is
low CO2 and this aids the shape change
• When one Hb PP binds O2, it changes shape
and that of the other 3 so that they take up
O2 more easily. The shape change increases
the affinity of Hb for O2.
What properties has it got?
• Easily associates with O2 where gas
exchange occurs (a high pO2and low
pCO2).
• Readily dissociates with O2 in the
tissues (a high pCO2 and low pO2).
• Some Hbs have a high O2 affinity, some
have low affinity.
Loading oxygen
• Some Hbs have a high O2 affinity, some
have low affinity due to shape.
• High affinity – organisms in a low O2
environment need as much O2 as possible.
They have low metabolic rates so its
unimportant that they release the O2
slowly.
• Low affinity – organisms in a high O2
environments have a high metabolic rate so
need O2 fast so needs to be released fast.
Unloading oxygen
• In the tissues there is a low pH due to
high pCO2.
• The shape of one Hb pp changes so that
it will release the O2 easily. This leads
the other 3 to do so.
• In the presence of high pCO2 Hb has a
reduced affinity for O2.
• The higher the pCO2 the more readily
O2 is released (Bohr effect).
Task
• Pick a number
– All 1s get together and research the structure
of Hb.
– All 2s get together and research the
properties of Hb.
– All 3s get together and research why we have
different Hbs and how they work.
– All 4s get together and research how Hb loads
and unloads O2.
• You now need to get into groups with a 1,
2,3 and a 4 to get a complete set of
information.
Learning outcomes
• Describe the structure of haemoglobin using
knowledge of protein structure D
• Explain the role of Hb in the transport of
oxygen C
• Explain the properties required by Hb in the
transport of oxygen C
• Sketch oxygen dissociation curves and explain
their features B
Oxygen dissociation curves
How much Hb contains oxygen
O2 in the lungs/arteries
O2 in the tissues
O2 in the veins
How much of the atmosphere is due to oxygen
Homework
• Sketch an oxygen dissociation curve for
adult Hb. Add in where you think foetal
haemoglobin and myoglobin curves
should go and explain why
• Exam Q5 with carbon dioxide effects