Lecture #4

Question 1

Explain why the hemoglobin O2 affinity curve is sigmoidal

Answer 1

• 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

Question 2

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)

Answer 2

least -> middle -> most

pigment B -> pigment C -> pigment A

Question 3

How do hemoglobin and myoglobin interact to ensure O2 delivery to muscle? And maternal and fetal hemoglobin to ensure O2 delivery to the fetus?

Answer 3

• 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

Question 4

Which organisms have hemocyanin?

Answer 4

• some gastropods, some bivalves, all cephalopods

- most crustaceans, arachnids, and centipedes

Question 5

What are the similarities and differences between hemoglobin and hemocyanin?

Answer 5

• 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

Question 6

For a given respiratory pigment (or blood), what is the difference between “oxygen binding affinity” and “oxygen carrying capacity”?

Answer 6

• 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

Question 7

For Antarctic ice-fishes, what is a major disadvantage of not having hemoglobin?

Answer 7

• 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

Question 8

How are Antarctic ice-fishes still able to deliver enough oxygen for aerobic respiration to tissues?

Answer 8

-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

Question 9

What other physiological adaptations do Antarctic ice-fishes posses?

Answer 9

• “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