Structure of Myoglobin and Hemoglobin

Notes:

Myoglobin (Mb) is a protein used for O2 storage in muscles. It is a single chain polypeptide, meaning it only has tertiary structure. 

Hemoglobin (Hb) is a protein that is responsible for O2 transport. It has quaternary structure and is considered a "dimer of a dimer", meaning it is a tetramer containing 2 dimers that come together to make yet another dimer. These subunits are 2𝞪 and 2𝛃. (2𝞪,2𝛃). 

Each subunit of hemoglobin functions very similarly to a myoglobin protein. Therefore, the following description will apply for both myoglobin and one subunit of hemoglobin. 

These proteins contain a heme group that binds O2. This heme group is an iron atom bound to four nitrogen atoms. This leaves a 5th site to be open to bind to a proximal histidine as well as a 6th site above this that can bind to oxygen. 

When oxygen binds to this area, the Fe (iron) atom moves up and into the ring towards it. As O2 pulls electrons towards itself, it lets Fe get "smaller" and therefore fit into the ring. It then pulls the histatine with it, which in hemoglobin goes on to create a conformational change. Additionally, the distal histidine helps ensure the proper binding of O2 to this location, which is stabilized by a hydrogen bond. 

Note: There is a bit of extra information, so to get the most out of the video with any time constraints, feel free to stop at around 3:30.