Chapter 7 Flashcards
Myoglobin & Hemoglobin
What kind of protein is Myoglobin? (structure, type, and where? ICF or ECF?)
Monomeric (single polypeptide chain), globular, and intracellular
What are the two types of Myoglobin?
Deoxymyoglobin and Oxymyoglobin
How many molecules of O2 does Myoglobin bind to?
1 molecule of O2
What kind of structure is Hemoglobin?
heterotetramer (2 alpha and 2 beta sub-units)
How many molecules of O2 does Hemoglobin bind to?
4 molecules of O2
What are the functions of Myoglobin?
1) Increases O2 solubility in tissues
2) Facilitates O2 diffusion
3) Stores O2 in tissues
What are the functions of Hemoglobin?
Transports O2 from lungs to peripheral tissues (erythrocytes)
What ring surrounds 4 of the six ligands of Hemoglobin?
Porphyrin ring (The iron binds to the 4 N atoms of the 4 pyrrole rings)
What is connected to the fifth coordination site on Hemoglobin?
Proximal histidine (Fe connects to the N of the histidine ring) imidazole ring of a histidine
What is connected to the sixth coordination site on hemoglobin?
O2 (O=O)
What stabilizes the sixth coordination site?
Distal histidine
What is the function of the distal histidine?
Prevents oxidation of the Fe and reduces CO (carbon monoxide) from binding to the Heme
In deoxyhemoglobin, where does the Fe lay? In what plane?
Lies slightly outside of the porphyrin ring
In oxyhemoglobin, where does the Fe lay? In what plane?
Moves into the plane of the porphyrin ring
Basically, when the Hemoglobin becomes oxidized there will be a shift. The beta and alpha subunits will push one each other
What are the two versions/states of Hemoglobin?
T state (deoxy) and R state (oxy)
Why is it important to know the primary structure?
Because the structure dictates the function and knowing the structure of the proteins can better our understanding of species (Amino acids are conserved in hemoglobin among species)
What are the main conformational changes in a hemoglobin chain when it is induced by oxygenation?
When the O2 binds, it basically pulls the HIS ring up towards the porphyrin ring. The QUATERNARY structure changes when the O2 binds.
The iron moves into the plane of the protoporphryin ring.
T state is also known as the ?
Tense state
R state is also known as the ?
Relaxed state
When Hemoglobin is oxidized, what two amino acids start interacting?
-Asparagine and +Aspartate
Does the cavity of Heme shrink of enlarge when it becomes oxidized?
Shrink
What is the organic component of the Heme group?
protoporphyrin
What kind of curve does Hemoglobin have?
Sigmoidal
What kind of curve does Myoglobin have?
Hyperbolic
Why sigmoidal curve of Hb better than the hyperbolic curve of Mb?
More O2 is getting delivered to the tissues from the lungs from hemoglobin (66%) versus myoglobin (7%)
What is an allosteric enzyme?
Allosteric enzymes are enzymes that change their conformational ensemble upon binding of an effector, which results in an apparent change in binding affinity at a different ligand binding site.
What is cooperative binding? And what is an example?
the binding of one ligand (ex. O) to a protein that influences the affinities for the ligand of the other binding sites on the protein
Ex: The binding of O2 in heme
What is Affinity?
liking for more of the same molecules/tightness
What is the Homotropic effect?
If the interacting sites bind all the same ligand
What is the Heterotropic effect?
If the interacting sites bind different ligands
What are allosteric effectors/modulators?
They bind to a protein at a site separate from the functional binding site (may be activators
or inhibitors)
What are the two models of the T and R state?
concerted and sequential which actually both happen at the same time
How do you find the p50 of a graph?
you find the 50% saturation mark and draw a line straight down and that will tell you the p50
The smaller the p50 the _______ affinity for oxygen
HIGHER, creates more binding for a lower p50
this means it will NOT release as much O2 in the tissues
The higher the p50 the ________ oxygen is unloaded
MORE and with less affintiy
What are the three allosteric effectors?
1) Bisphosphoglycerate
2) Protons
3) CO2
What are in RBC that makes the O2 release more?
2,3-BPG
What does 2,3-BPG bind to? What charges does it look for?
It will bind to Histidine and Lysine
The negative charges on 2,3-BPG bind to the positive charges of the HIS and LYS
What form of Hemoglobin does 2,3-BPG bind to?
T state/form DEOXY
Stabilizes the T state because the T state can accommodate the 2,3-BPG while the R state can NOT accomodate
What two chains do Fetus’s use in O2 transport?
alpha and gamma
fetus wants to retain more O2 thats why they have gamma instead of beta
What amino acid change in a fetus makes the difference from the chain being a gamma instead of a beta?
It changes from a (+) histidine to a serine (with OH group and is neutral) this makes for lower affinity for 2,3-BPG meaning the 2,3-BPG will not bind to the serine as well as it did the histidine
Will the graph of a fetus have more or less O2 unloading?
LESS it retains more O2 which would make the graph shift left
As 2,3-BPG increases it stabilizes ______ state so the ______ oxygen is released which means for a higher p50
T state, MORE
The higher the altitude, which way does it make the graph shift?
Right because an increase in 2,3-BPG (lwoer affinity and MORE O2 released) at high altitudes which causes efficient oxygen to unload into the tissues
What is the BOHR effect
the response of hemoglobin for a change in pH and CO2
If you have pH of 7.2, how does this affect the graph shift and what state will be stabilized?
this will make the graph shift right because more O2 will be released (having more H+), the T state will be stabilized
If you have pH of 7.6, how does this affect the graph shift and what state will be stabilized?
You will have stabilization of the R state and the graph will shift left because you have (less H+) and more O2 will be retained
As the pH rises, becomes more BASIC, how will the graph shift?
The graph will shift left because His cannot form hydrogen bond with Asp because His no longer protonated= this promotes oxygen binding (stabilizes R state). Oxygen retained
At low pH, more ACIDIC, how will the graph shift?
The graph will shift right because His is protonated and forms ionic binds with Asp= more Oxygen is released (stabilizes T state) more O2 gets released
What interacts with the terminal amino groups and helps stabilize the salt bridge interactions? (This stabilizes the T state of Hb)
carbamate
The R state is stabilized what?
oxygen binding to any heme group
increased pH
release of 2,3 BPG
decreased CO2
T form is stabilized by what?
oxygen released from any heme
decreased pH
binding of 2,3 BPG
increased CO2
What amino acid causes the change in sickle cell disease?
Glutamine to Valine
changes from a negative to hydrophobic
Where is the mutation in Sickle Cell Anemia found?
on the β chain
What do sickle cells do when they rupture?
-causes the release of iron
-Increase in iron leads to
the formation of reactive
oxygen species (ROS) that
damage lipid and protein
components of the cell.
-Sickle Cell Anemia can lead to
Secondary Hemochromatosis (overdose of iron)
–the only way to help someone like this is to pump blood out of them
What is the mechanism of formation of hydrophobic patches in sickle cell anemia?
- In the T state, the valine will be protruding out trying to find another partner to hide itself (hydrophobic) and this forms patches between Hb’s
- –This reduces the solubility of deoxy but not the oxy from of Hb.
- Sickling occurs when there is a high conc of deoxy Hb.
What does THALASSEMIAS stand for?
Misfunctioning Hb genes where
1) One or more of the genes coding for hemoglobin chains may have been deleted
2) One or more genes may be shortened
What is β-Thalassemia?
- β globin is lost or cannot be expressed
- Homozygous: rely on γ chains
- Heterozygous: one β gene is functional
What is α-Thalassemia?
- can have 0, 1, 2, ,3 or 4 copies of α chains
- Low levels of α chains compensated with production of β4 or γ 4 tetramers
- Can make beta or gamma chains overexpressed
