Respiratory Physiology Lecture 5 Part 25: Cooperative Binding and the O2 Dissociation Curve

Question 1

What happens to heme when O2 combines with it?

Answer 1

When O2 binds to a HEME group, it deforms the shape of the HEME group which changes the shape of its associated globin chain from tense (T) to relaxed (R) state

Question 2

What is cooperative binding of oxygen with heme?

Answer 2

The change in the shape of one globin chain of the heme due to attachement of oxygen deforms the others, exposing the iron in their HEME groups and facilitates binding of additional O2 molecules

Question 3

What curve does cooperative binding of O2 with heme create?

Answer 3

This cooperative binding action produces the characteristic sigmoidal oxygen binding curve of Hb

Question 4

What are the important regions of the sigmoidal dissociation curve Hb saturation?

Answer 4

1. Flat portion (Plateau) between 60 - 100 mmHg
2. Steep portion between 10 - 40 mmHg
3. Steep portion between 40 - 60 mmHg

Question 5

Plateau of oxyhemoglobin dissociation curve

Answer 5

higher oxygen tension between 60-100 mmHg → range that exists at the pulmonary capillaries

• Due to plateau, saturation stays high over widevrange of alveolar PO2 (With drop in PO2 to 60 mmHg, saturation drops only 10 %)
• Provides safety factor so that even a significant limitation of lung function still allows almost normal oxygen saturation of Hb.

Question 6

What can reduce the plateau in the oxyHb dissociation?

Answer 6

many conditions result in reduced alveolar PO2 and therefore arterial PO2

• (Pulmonary diseases, altitude)

Question 7

Steep portion (40-60 mmHg) of oxyHb dissocation curve

Answer 7

range that exists at the systemic capillaries

unload large amounts of O2 with only small decrease in PO2. At PO2 of 40 mmHg O2 saturation of Hb is still 75 %.

Question 8

Why is it important that P_O2 remain high in the peripheral capillaries?

Answer 8

It is important that PO2 remains relatively high in the capillary of peripheral tissue since this pressure is necessary to drive diffusion of O2 from RBC, to blood to cells and mitochondria

Question 9

What can enhance O2 unlaoding in the peripheral tissue?

Answer 9

Because PO2 in the capillary of peripheral tissue is on steep portion, small changes in shape of dissociation curve due to compounds produced in tissues (pH, temperature) enhance O2 unloading