Haemoglobin and Myoglobin. Flashcards
A globular protein is in what form of protein structure?
Tertiary.
What are the characteristics of a globular protein?
They are spherical in shape.
They are water soluble.
They can be used as transport proteins or enzymes.
If a globular protein contains heme, where will the heme likely be found?
Heme will be bound to a domain within the globular protein.
Heme is an example of what kind of protein attachment?
A prosthetic group.
What are the functions of hemeproteins?
They can function as electron carriers.
They can be part of an active site.
Transport of O2 and CO2.
Storage of O2.
What are 2 examples of hemeproteins?
Myoglobin.
Haemoglobin.
What is the structure of heme?
A porphyrin ring with an iron atom at its centre.
The porphyrin ring of heme is an example of what kind of protein feature?
A coenzyme.
The iron atom of heme is an example of what kind of protein feature?
A cofactor.
How many bonds can iron form?
6.
How does iron bind to the porphyrin ring?
4 of the bonds are bound to 4 nitrogen atoms that are part of the porphyrin ring.
Heme will insert itself into what level of structure in myoglobin?
The tertiary structure.
Heme will insert itself into what level of structure in haemoglobin?
The quaternary structure.
Where does oxygen bind to in myoglobin or haemoglobin?
To the heme molecule.
What part of the heme molecule will oxygen bind to?
The iron atom.
What are the 2 free bonds of iron bonded to when heme is oxygeated.
One bond is bound to one of the oxygens of O2.
One bond is bound to proximal histidine.
What is oxygen bound to within the heme molecule?
One oxygen is bound to the iron of heme.
One is bound to distal histidine.
Why does an oxygen atom bind to distal histidine?
Because the distal histidine stabilises the oxygen.
What does the proximal histidine do to for heme molecule?
It stabilises the positioning of heme.
What shape is de-oxygenated heme?
Non planar.
It is domed.
What shape is oxygenated heme?
It is planar.
The bonding of oxygen to heme straightens it out.
What is the function of myoglobin?
Myoglobin is used for storing oxygen.
Describe the secondary structure of myoglobin?
It is made up of many different alpha helices that are separated by beta bends and random loops.
Where is heme located in myoglobin?
In a domain at the centre of the protein.
How many oxygens does myoglobin bind to?
1.
Does myoglobin suffer from allosteric effectors?
No.
Myoglobin is at what level of protein structure?
Tertiary.
Is myoglobin a single or multiple polypeptide?
A single polypeptide.
Where is haemoglobin found in the body?
Only in red blood cells.
What is the function of haemoglobin?
To transport oxygen around the body.
What level of protein structure is haemoglobin at?
Quaternary.
How many polypeptides make up haemoglobin?
4.
How are the 4 subunits of haemoglobin divided up?
Into an alpha dimer and a beta dimer.
How are the 4 dimers of heme arranged?
Dimer 1 is made of an 1 alpha dimer and a beta dimer.
Dimer 2 is made up of a beta dimer and an alpha dimer.
How many heme molecules are found in haemoglobin?
4.
How many heme molecules are found in myoglobin?
1.
How many oxygens can haemoglobin bind to?
4.
What holds the dimers of haemoglobin together?
Non covalent bonds.
What happens to the bonds that hold the 2 dimers together when an oxygen binds to a heme?
Some of the bonds are broken so the forces holding the 2 hemes together are weaker.
What is the taut form of haemoglobin?
The form of haemoglobin that is not bound to oxygen.
This is because the bonds holding the dimers together are stronger as there are more of them.
What is the relaxed form of haemoglobin?
The form of haemoglobin that is bound to oxygen.
This is because the bonds holding the dimers together are weaker as there are fewer of them.
What kind of affinity for oxygen does taut haemoglobin have?
Low affinity.
What kind of affinity for oxygen does relaxed haemoglobin have?
High affinity.
How does the affinity of haemoglobin to oxygen change?
It changes depending on the amount of oxygen available.
What are the allosteric effectors that influence hemes binding affinity for oxygen?
Partial pressure of oxygen
pH of the environment.
Partial pressure of CO2.
The availability of 2,3-bisphosphoglycerate.
Does myoglobin have a high or low affinity for oxygen?
Very high.
What happens to haemoglobin’s affinity for oxygen when an oxygen molecule binds to de-oxygenated heme?
As more oxygen binds to haemoglobin its affinity for oxygen will increase.
When 1 oxygen binds to a heme group, the affinity for oxygen of the other heme groups increases.
Is the partial pressure of oxygen higher in the tissues or the lungs?
The lungs.
Myoglobin has what kind of shape on an oxygen dissociation graph?
Hyperbolic.
What does the p50 of myoglobin or haemoglobin represent?
The partial pressure of oxygen where they will lose 50% of their oxygen.
Is the P50 higher form myoglobin or haemoglobin?
Haemoglobin.
In what organ will haemoglobin be fully saturated with oxygen?
In the lungs.
What happens when haemoglobin travels away from the lungs and goes to the tissues?
It will lose oxygen as the partial pressure of oxygen decreases.
What shape is haemoglobin on an oxygen dissociation graph?
Sigmoidal.
What happens when haemoglobin is shifted to the left on the oxygen dissociation graph?
Its affinity for oxygen will increase.
What happens when haemoglobin is shifted to the right on the oxygen dissociation graph?
Its affinity for oxygen will decrease.
How strong are the bonds between the 1st O2 to bind to haemoglobin and the hem group?
They are very weak.
As each subsequent oxygen binds to its heme, the bonds to each one will get stronger.
Why does haemoglobin off load O2 in the tissues?
Because the partial pressure of O2 is much lower in the tissues.
What happens when haemoglobin has off loaded all of its oxygens?
It will start to pick up CO2 molecules that have been made by the tissues.
What happens to CO2 once it has bound to heme?
It will be transported back to the lungs where it will be exhaled.
Does CO2 bind to the heme groups in haemoglobin?
No.
CO2 binds to the 4 amino groups of the subunits that make up haemoglobin.
What can compete with O2 to bind with haemoglobin?
Carbon monoxide.
Does heme have stronger affinity for CO2 or CO?
CO.
What effect will 1 CO molecule that is bound to a heme have on the 3 other heme molecules in haemoglobin?
If one heme is bound to a CO, then it will affect the affinity for oxygen of the other heme groups and they will form much stronger bonds with oxygen.
How does heme behave if it is bound to 1 CO and 3 O2’s?
It will behave like myoglobin and will not deliver O2 to the tissues.
What will shift the oxygen dissociation curve of haemoglobin to the left and changes the sigmoidal curve to a hyperbolic curve?
If carbon monoxide is bound to a heme molecule.
What kind of acid is formed when there are high levels of CO2 within the body?
Carbonic acid which dissociates to form bicarbonate and H+.
What affect does high levels of CO2 have on the pH in that area of the body?
High levels of CO2 will decrease the pH.
What affect does low pH have on haemoglobin?
Any drop in pH will make it easier for haemoglobin to off load oxygen to the affected area.
What is the Bohr effect?
The decreased affinity of haemoglobin for oxygen under acidic conditions.
An increase in CO2 leads to what in the surrounding tissues?
Acidification.
How can a drop in pH due to increased CO2 levels be corrected?
By adding more O2 to the affected area.
When are the bonds between the 2 dimers of haemoglobin at their strongest?
When haemoglobin has no oxygen bound to it.
Does deoxygenated haemoglobin have low or high affinity for O2?
Low.
How does tissue acidification affect the structure of haemoglobin?
The structure of haemoglobin will go from the relaxed form to the taut form by increasing the number of bonds between the subgroups.
If the amount of CO2 increases, or the pH decreases, how will this affect the oxygen dissociation curve of haemoglobin?
It will shift it to the right, representing haemoglobins decreased affinity for oxygen.
If the amount of CO2 decreases, or the pH increases, how will this affect the oxygen dissociation curve of haemoglobin?
It. will shift to the left, representing haemoglobins increased affinity for oxygen.
Hb-O2 + H+ = ???
Hb-H+ + O2.
When is 2,3-bisphosphoglycerate made?
During glycolysis.
Where does 2,3-BPG locate itself in the haemoglobin molecule?
In the positively charged cavity between the 4 subunits of haemoglobin.
What effect does 2,3-BPG have on haemoglobin?
It stabilises the de-oxy form of oxygen allowing for oxygen to be offloaded much more easily.
What will increase the concentration of 2,3-BPG in haemoglobin?
When a person is at high altitudes.
An increased amount of 2,3-BPG will shift the oxygen dissociation curve for Hb in what direction?
If the concentration of 2,3-BPG is increased, it will shift the oxygen dissociation curve to the right.
