Explain why the hemoglobin O2 affinity curve is sigmoidal
- the cooperativity of hemoglobin causes this
- after one subunit is bound, it increases the favorability of another subunit binding O2 by changing the shape of the hemoglobin (causes increasing attraction to O2)
- this leads to the more rapid increase as opposed to a linear relationship
Consider three respiratory pigments with the following P50 (in brackets): pigment A (P50=20 mmHg; pigment B= 40 mmHg; pigment C (25 mmHg). Arrange them in increasing order of O2 affinity (from less affinity to more affinity)
least -> middle -> most
pigment B -> pigment C -> pigment A
How do hemoglobin and myoglobin interact to ensure O2 delivery to muscle? And maternal and fetal hemoglobin to ensure O2 delivery to the fetus?
- hemoglobin has a lower oxygen affinity than myoglobin, so the oxygen will be more attracted to the myoglobin and will be transferred there
- ensures that the oxygen is transferred to the myoglobin so it can be stored in the muscles
- hemoglobin has a lower oxygen affinity than fetal hemoglobin, so the oxygen will similarly transfer from the mother to the child
Which organisms have hemocyanin?
- some gastropods, some bivalves, all cephalopods
- most crustaceans, arachnids, and centipedes
What are the similarities and differences between hemoglobin and hemocyanin?
- hemocyanin has no cooperativity but hemoglobin does
- hemocyanin uses copper and hemoglobin uses iron
- hemocyanin does better in oxygen-poor regions and hemoglobin does better in oxygen-rich
- hemocyanin is in the hemolymph (fluid inside of invertebrates) while hemoglobin is in the blood
- hemocyanin has higher O2 affinity but hemoglobin has higher O2 capacity
For a given respiratory pigment (or blood), what is the difference between “oxygen binding affinity” and “oxygen carrying capacity”?
- oxygen binding affinity describes how efficient the compound is at extracting oxygen from the environment
- oxygen carrying capacity describes how much oxygen the compound can bind to/transport at one time
For Antarctic ice-fishes, what is a major disadvantage of not having hemoglobin?
- they have very low O2 carrying capacity and must pump a lot of blood to extract enough O2 from the water
- this expends more energy
How are Antarctic ice-fishes still able to deliver enough oxygen for aerobic respiration to tissues?
-they pump more blood and spend ~4-5 times as much energy pumping blood to be able to process enough water to extract the necessary amount
What other physiological adaptations do Antarctic ice-fishes posses?
- “Sluggish” life style
- Large gills
- Large blood volume (4-fold higher than other fishes)
- Large hearts (4-fold larger than other fishes)
- High degree of vascularization
