Question

What is the structure of hemoglobin and how is oxygen bound to it?

Hemoglobin is made of two protein subunits. Within each subunit, is a heme group made of nitrogen and calcium. The heme groups bind to oxygen.

Hemoglobin is made of six protein subunits. Within each subunit, is a heme group made of hydrogen and iron. The heme groups bind to sulfur.

Hemoglobin is made of four protein subunits. Within each subunit, is a heme group made of nitrogen and iron. The heme groups bind to oxygen.

Answer 1

The last option is correct about the structure of hemoglobin. Hemoglobin is made of four subunits. Each subunit contains a polypeptide chain called globin and a heme group. So there are 4 polypeptide chains (globin chains), two of which are called alpha chains and the other two are beta chains. Each polypeptide chain is associated with a heme group which has iron at the center. It is the oxygen binding site.

So 1 hemoglobin molecule - has 4 heme groups (each heme group binds to an oxygen molecule)

Thus 1 hemoglobin molecule - can carry 4 oxygen molecules.

Answer 2

The correct answer would be "Hemoglobin is made of four protein subunits. Within each subunit, is a heme group made of nitrogen and iron. The heme groups bind to oxygen".

Hemoglobin is a protein exists in quaternary structure. It has four sub-units namely 2 alpha subunits and 2 beta subunits. The structure is denoted as α₂β₂.

The subunits are bound together with the help of hydrogen bonds, salt bridges, and hydrophobic interactions.

Each subunit consists of a protein chain and a prosthetic group termed as heme which consists of iron ion and a porphyrin ring. The iron and the four nitrogen atoms lie in one plane in the center of the ring.

This iron serves as the oxygen binding site in the hemoglobin.