There's a bit of a misunderstanding here. It's not a polypeptide chain that has haem molecules attached to it, but a protein called haemoglobin.

Here's the breakdown:

* Haemoglobin is a protein found in red blood cells that is responsible for carrying oxygen throughout the body.

* Haemoglobin is made up of four polypeptide chains (two alpha and two beta chains).

* Each polypeptide chain has one haem molecule attached to it.

* Each haem molecule can bind to one oxygen molecule.

Therefore, a haemoglobin molecule has four haem molecules attached to it, allowing it to bind and carry four oxygen molecules at a time.