Hemoglobin and Myoglobin Flashcards
What is myoglobin
A globular protein that is found in skeletal and cardiac muscle in almost all vertebrates and mammals.
Has a higher O2 affinity than Hemoglobin
Stores O2 and uses it as a reserve for when the demand for O2 cannot be totally satisfied by Hemoglobin
O2 is stored on a heme group found in it’s single polypeptide chain
It’s 80% alpha-helix. It’s a monomer so it has no quaternary structure
The hydrophobic parts of the protein fold inward and the polar parts are on the outside of the structure making it hydrophilic and soluble in water.
The heme group (prosthetic group) sits on a crevice lined by non-polar amino acids.
Myoglobin is the heme(iron containing) protein responsible for the color of meat. The more Mb the darker the meat.
It can only bind one O2 molecule because it only contains one heme
It’s found in large quantities in muscle and heart cells. When there is significant muscle or heart damage the blood contains a large number of Mb proteins. If you have too many of thesein the blood it can cause kidney damage. (Rhabdomyolysis)
What do high amounts of myoglobin allow you to do?
It allows you to hold your breath for long amounts of time
ex: Whales and Seals
Hemoglobin
A globular protein with 4 polypeptide chains
- 2 alpha chains
- 2 beta chains
Similar to Myoglobin in 1st, 2nd, and 3rd protein structure.
Each chain has a heme group with its Fe2+ iron, so it can carry four O2 molecules
When Hb is deoxygenated, a molecule called BPG is held in its central cavity
Contained in red blood cells.
It is a better transporter than Mb. Hb is an allosteric protein that shows cooperative binding. When it binds to O2, it goes through a conformational change that makes it have more affinity to O2, and so on down the line until it has four O2
When it loses O2, then all the other O2 are also lost more readily.
What can Hb bind to?
O2 - HbO2 - Oxyhemoglobin
CO - HbCO - Carboxyhemoglobin
CO2 - HbCO2 - Carbaminohemoglobin
What effects do pH and CO2 have on Mb and Hb
Mb - little to no effect due to CO2 or pH
Hb - CO2 and H+ promote the release of O2. Hb decreases its affinity for O2. This is called the Bohr effect
What is the bohr effect
As CO2, Temperature, BPG, and H+ increase the binding affinity of Hb decreases.
Co2, BPG, and H+ bind to Hemoglobin reducing it’s affinity.
As cells undergo rapid metabolism the H+, BPG, Co2 and temp increase causing O2 to be released where it is needed.
What is BPG?
It is a byproduct of glycolysis.
Exercising muscles rapidly undergo glycolysis and also the intermediates used in other pathways.
BPG is released from the exercising muscles.
BPG binds in the donut hole of the HB greatly reducing the affinity for O2 (by a factor of 26)
At higher altitudes the amount of BPG is increased substantially to make up for the decreased pressure. This is why acclimatization is important in mountaineering
Fetal Hb
Fetal Hb
Has two alpha chains and two gamma chains
Binds BPG less readily and therefore shifts the curve to the left.
Has more affinity for O2
What has a higher affinity for O2? Mb or Hb?
Mb has a much much greater affinity for O2
What are the two forms of Hb and how does it affect affinity?
The two forms of Hb are:
- T form:
- Less affinity for O2
- deoxyhemoglobin
- R form:
- Higher affinity for O2
- oxyhemoglobin
Haldane Effect
The T-form (deoxyhemoglobin) of Hb increases its ability to carry CO2
The removal of O2 from Hb will increase its affinity for CO2
Hb-CO2
Carbaminohemoglobin
CO2 binds to the amino groups of lysine and arginine residues in hemoglobin
What shifts the Hb curve to the right? (reduced affinity)
- Increase in temp
- Increase in BPG
- Increase in CO2
- Increase in H+ or decrease in pH
- Increase of acidity
How does CO affect O2 affinity of Hb
CO binds 240 times more easily than O2, so the affinity for O2 decreases and shifts the curve to the left
What is the mutation of sickle cell anemia? (Favorite DAT question)
A glutamic acid is converted to a valine.
The mutation occurs on the hemoglobin Beta chain
This decreases the carrying capacity of Hb and causes pain as the blood vessels get clogged in places by the sickle shaped cells.
