Hemoglobin and Gas Exchange Flashcards
Gas exchange steps: oxygen to hemoglobin
- O2 is breathed in
- O2 is pulled in to lungs by pressure difference between lungs and nostrils
- O2 flows from bronchi to bronchioles to alveoli to membrane lining to blood stream
- O2 is loaded onto red blood cells (goes from higher concentration in lungs to lower concentration in RBC)
- O2 binds to hemoglobin (cooperative binding: hemoglobin is transformed to high O2 affinity state)
Gas exchange steps: hemoglobin to CO2
- Hemoglobin carries O2 to tissues
- Acidic environment promotes release of O2 into tissues
- CO2 is picked up by RBCs (CO2 is either attached to Hb or H2O by carbonic anhydrase)
- CO2 is transported to lungs
- CO2 goes down concentration gradient: flows from RBCs to lungs
- CO2 is breathed out
Heme group
Iron-containing group in myoglobin and hemoglobin
Iron can form 6 bonds
Allows myoglobin and hemoglobin to bind to oxygen
Causes color in urine, feces, and bruises
Myoglobin
Oxygen-binding protein in muscles
All or nothing: only kicks on in high or low oxygen concentrations (good in muscle, where O2 levels can become very low)
Hemoglobin
Oxygen-carrrying protein in RBCs
Essentially duplications of myoglobin (4 polypeptides instead of 1)
Has higher oxygen carrying capacity than myoglobin
Releases O2 at higher O2 levels than myoglobin: better for rest of body, where metabolizing tissues are at about 20% O2
Oxygen binding and shape change of heme
Oxygen binding “shrinks” the heme’s iron, allowing it to move into the heme plane
Shift in electron density creates a change in the magnetic properties (fMRI: measure blood flow to different parts of brain)
Formation of reactive oxygen species
Oxygen binding can result in oxidation of Fe+2 to Fe+3, making a superoxide ion (reactive oxygen species)
If ROS is released, no new O2 can bind: problem
Solution to problem: another His in globin prevents departure of ROS
Cooperative binding
Binding of 1 O2 molecule makes it more likely for others to bind
1 subunit of hemoglobin is altered, causing the other 3 to be altered
Binding to heme causes subunit shift
T state
“Tight” state: deoxyhemoglobin
R state
“Relaxed” state: oxyhemoglobin
2,3-Bisphosphoglycerate (2,3-BPG)
Molecule present in RBCs at about same level as hemoglobin
Stabilizes T state by “fitting in” H-bonds
Allosteric effector
Influences binding from a site different from the binding site
Ex: 2,3-BPG
Fetal hemoglobin
Contains gamma subunits: less 2,3-BPG binding
Causes fetus to hold onto O2 longer than mom: ensures that O2 flows from mom to baby and not other way around
Bohr effect
Decrease in pH causes O2 to come off hemoglobin at lower pressure
HCO3- (formed from reaction of H2O and CO2) binds to hemoglobin, causing release of O2 and transportation of CO2
Carbonic anhydrase
Catalyzes reaction of water and CO2
Formation of salt bridges between amino acids in Hb
Stabilize T state
Can only form at low pH
Carbamate ion
Result of CO2 binding to N-terminus of Hb
Stabilizes T-state and provides mechanism for CO2 transport to lungs
Purposes of CO2 acquisition
Increase O2 release (stabilize T state)
Provide clearance of CO2 (CO2 is carried to lungs, where it is released)
Cause of sickle cell anemia
Glu in hemoglobin is mutated to Val
Hydrophobic interactions can occur between Val and Phe
When hemoglobin is in T state, more hydrophobic interactions can occur, creating insoluble fibrils
