7.1 haemoglobin

Question 1

What are haemoglobins?

Answer 1

• a group of chemically similar molecules found in a wide variety of organisms.
• proteins with a quaternary structure allowing them to load oxygen under one set of conditions and unload it under another.

Question 2

Describe the structure of haemoglobin.

Answer 2

PRIMARY: the sequence of amino acids in the 4 peptide chains
SECONDARY: each chain is coiled into a helix
TERTIARY: each shape is folded into a precise shape so that it can carry oxygen.
QUATERNARY: all 4 polypeptides are joined to form an almost spherical shape. Each polypeptide is joined to a haem group containing a ferrous (FE2+) ion. Each ion can combine with a single oxygen molecule, meaning 4 are carried by a single haemoglobin molecule.

Question 3

What is loading/associating?

Answer 3

The process by which haemoglobin binds to the oxygen in the lungs

Question 4

What is unloading/dissociating?

Answer 4

the process by which haemoglobin releases oxygen in the tissues

Question 5

How does affinity effect loading/unloading?

Answer 5

• haemoglobins with a high affinity for oxygen take it up more easily but release it less easily
• haemoglobins with a low affinity for oxygen take it up less easily but release it more easily

Question 6

What is the role of haemoglobins and what does it need to perform this?

Answer 6

• Its role is to transport oxygen. to do this it must:
• readily associate with oxygen at the gas exchange surface
• readily dissociate at tissues requiring oxygen

Question 7

How does haemoglobin readily associate/dissociate with oxygen?

Answer 7

• It changes affinity to oxygen under different conditions

- its shape changes in the presence of carbon dioxide so i binds to oxygen more loosely.

Question 8

Why are there different haemoglobins?

Answer 8

• haemoglobin from different species have different affinities for oxygen
• this is because they have different primary structures, so different 3D shapes and oxygen binding properties.