Question

• In your own words (and approximately 250 words), explain why adult haemoglobin (HbA) is better suited for its job as the oxygen-carrying protein in red blood cells compared with myoglobin and the sickle cell form of haemoglobin (HbS). In addition, how does foetal haemoglobin (HbF) compare and why do we have this form of Hb??

Include in your answer:

• An introduction to haemoglobin (HbA) and the way in which its structure underlies its function.
• The way in which Mb differs from HbA and thus why it is unsuitable for the job HbA does.
• The way in which HbS differs from HbA, the consequences of this and thus why it is less suitable for the job HbA does.
• The way in which HbF differs from HbA and what its function is.

Answer 1

Hemoglobin is contained in red blood cells, which efficiently carries oxygen from the lungs to the tissues of the body. It also helps in the transportation of carbondioxide and hydrogen ions back to the lungs.

It consists of four subunits , each with a cofactor called heme group that has an iron atom at the centre.The iron is the main component that actually binds to oxygen , thus each hemoglobin molecule is able to carry four molecules of oxygen. Cooperation among the four subunits of the hemoglobin molecule is necessary for the efficient transportation of oxygen. The four subunits atcually bind to oxygen cooperatively , the binding of oxygen to one site of the four subunits will increase the likelihood of the remaining sites to bind with oxygen as well.

It is a protein that is used to carry oxygen through the bloodstream from lungs to the tissues . This is important for survival . It has lower affinity for oxygen the lower the concentration of oxygen gets. This has great implications for human body and has helped us adapt very effectively. The lower affinity and lower concentrations means that when we are working out, our bodies are low on oxygen which means hemoglobin has less affinity for oxygen and can more easily drop the oxygen off in human tissues. This gives us greater oxygen in our oxygen dependent state. When oxygen concentration is high , the hemoglobin has a higher affinity for oxygen and therefore doesnot drop the oxygen where it is not needed.  

MYOGLOBIN

It is a small oxygen binding protein found in muscle cells. Its function primarily in storing oxygen and faciliatating oxygen diffusion in muscle tissue. It is a single chain globular protein that consists of 153 amino acids and a heme group. The globular structure of myoglobin consists of mainly alpha helices linked together by various turns.It exists either in an oxygen free form called deoxymyoglobin or in a oxygen bound form called oxymyoglobin. Whether it binds to oxygen depends on the presence of the prosthetic group , heme. When myoglobon is able to bind oxygen , it serves as the primary oxygen carrying molecule in the muscle tissue. Its affinity for oxygen is higher than hemoglobin

Although it has much higher affinity for oxygen than its structural analog hemoglobin , myoblobin is a less efficient oxygen carrier for the cell. Because its affinity for oxygen is so high , myoglobin has a difficult time in letting go of the oxygen in the right areas. The cell needs oxygen to be distributed to the appropriate organelles , jsut as the body needs oxygen to be distributed to the right organ systems. This means that carries the oxygen must be capapble of releasing it once it reaches its assigned destination. iTS HIGHER AFFINITY FOR OXYGEN MEANS THAT IT WILL BE LESS INCLINED TO RELAESE THE OXYGEN ONCE IT HAS BEEN BOUND. This in turn means that it will be distributing less oxygen to those areas where it is needes.

THUS HEMOGLOBIN IS ATCUALLY A MORE EFFICIENT CARRIER FOR THE CELL SINCE ITS AFFINITY FOR OXYGEN IS LOWER.

FETAL HEMOGLOBIN -

The four hemes, which are the oxygen binding parts of hemoglobin , are similar between hemoglobin F and other types of hemoglobin A. The key feature allows hemoglobin F to bind more strongly to oxygen is by having gamma subunits istead of beta , In fact , some naturally occuring molecules in our body can bind to hemoglobin and change its affinity for oxygen. One of the molcules is 2,3-BPG and it enhances hemoglobin's ability to release oxygen. It interacts much more with HbA than HbF . This is beacuse the adult beta subunit has more positive charges than the fetal gamma subunit, which attracts the negative charges from 2,3-BPG . Due to the presence of 2,3-BPG for hemoglobin A , Hemoglobin F binds to oxygen with more affinity in average.

. One of the molecules s 2,3-bisphosphoglycerate (2,3-BPG) and it enhances hemoglobin's ability to release oxygen.[12] 2,3-BPG interacts much more with hemoglobin A than hemoglobin F. This is because the adult β subunit has more positive charges than the fetal γ subunit, which attract the negative charges from 2,3-BPG. Due to the preference of 2,3-BPG for hemoglobin A, hemoglobin F binds to oxygen with more affinity, in average.[13]