Hemoglobin and Gas Exchange

Question 1

Gas exchange steps: oxygen to hemoglobin

Answer 1

1. O2 is breathed in
2. O2 is pulled in to lungs by pressure difference between lungs and nostrils
3. O2 flows from bronchi to bronchioles to alveoli to membrane lining to blood stream
4. O2 is loaded onto red blood cells (goes from higher concentration in lungs to lower concentration in RBC)
5. O2 binds to hemoglobin (cooperative binding: hemoglobin is transformed to high O2 affinity state)

Question 2

Gas exchange steps: hemoglobin to CO2

Answer 2

6. Hemoglobin carries O2 to tissues
7. Acidic environment promotes release of O2 into tissues
8. CO2 is picked up by RBCs (CO2 is either attached to Hb or H2O by carbonic anhydrase)
9. CO2 is transported to lungs
10. CO2 goes down concentration gradient: flows from RBCs to lungs
11. CO2 is breathed out

Question 3

Heme group

Answer 3

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

Question 4

Myoglobin

Answer 4

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)

Question 5

Hemoglobin

Answer 5

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

Question 6

Oxygen binding and shape change of heme

Answer 6

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)

Question 7

Formation of reactive oxygen species

Answer 7

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

Question 8

Cooperative binding

Answer 8

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

Question 9

T state

Answer 9

“Tight” state: deoxyhemoglobin

Question 10

R state

Answer 10

“Relaxed” state: oxyhemoglobin

Question 11

2,3-Bisphosphoglycerate (2,3-BPG)

Answer 11

Molecule present in RBCs at about same level as hemoglobin

Stabilizes T state by “fitting in” H-bonds

Question 12

Allosteric effector

Answer 12

Influences binding from a site different from the binding site
Ex: 2,3-BPG

Question 13

Fetal hemoglobin

Answer 13

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

Question 14

Bohr effect

Answer 14

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

Question 15

Carbonic anhydrase

Answer 15

Catalyzes reaction of water and CO2

Question 16

Formation of salt bridges between amino acids in Hb

Answer 16

Stabilize T state

Can only form at low pH

Question 17

Carbamate ion

Answer 17

Result of CO2 binding to N-terminus of Hb

Stabilizes T-state and provides mechanism for CO2 transport to lungs

Question 18

Purposes of CO2 acquisition

Answer 18

Increase O2 release (stabilize T state)

Provide clearance of CO2 (CO2 is carried to lungs, where it is released)

Question 19

Cause of sickle cell anemia

Answer 19

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