# Define partial pressure of a gas

1. Define partial pressure of a gas. Identify 3 different units used to measure partial pressure.
2. Define torr.
3. What is the PO2 of the atmosphere at sea level? Express in units of torr.
4. Define respiratory pigment and heme.
5. Name the respiratory pigment found in vertebrates and the respiratory pigment common in decapod crustaceans. Identify the metal ion associated with the porphyrin rings of each respiratory pigmennt
6. How many subunits does vertebrate Hb have and what are they named?
7. To what part of the Hb molecule does O2 bind? How many oxygen binding sites does each Hb molecule have?
8. If a solution contains 1 x 106 Hb molecules, how many O2 binding sites are available? If the solution of Hb is 50% saturated with O2, how many binding sites are occupied by O2? If the Hb solution is 23% saturated with O2, how many binding sites are occupied by O2?
9. A solution of Hb is 98% saturated with O2 when the partial pressure of O2 is 100 mm Hg. What is the partial pressure of O2 in units of kPa?

Deer mice (Peromyscus maniculatus) have structurally different forms of Hb, depending upon whether they live at high or low altitude. A group of researchers collected deer mice from high and low altitude populations and drew blood from the mice. The oxygen binding properties of Hb from high altitude-dwelling and low altitude-dwelling mice were compared at 37°C and pH 7.4. Data from this comparison are given in the table below.
Using the data in the table below, draw a graph showing how the saturation of Hb binding sites changes as the partial pressure of oxygen changes. Points for Hb-B1 and Hb-B2 should be plotted on the same graph. – – in the table indicates no data were collected at that PO2 for that type of Hb.

 PO2 (torr) Percent saturation of Hb-B1 Percent saturation of Hb-B2 0 0 0 6 39 — 6.5 — 24 7 50 — 9.0 62 40 12 72 60 15 — 70
1. Which is the independent variable in this case?
2. Use your graph to estimate the PO2 at which Hb-B1 is 50% saturated with O2 (P50) and the PO2 at which Hb-B2 is 50% saturated with O2.
3. Define affinity of a molecule for a ligand.
4. Using your answer to question 12, which type of Hb has higher oxygen affinity?
5. Which form of Hb would you expect to find in deer mice living at high altitude where the PO2 of the atmosphere is less?
6. Which form of deer mouse Hb releases O2 more easily when blood circulates to body tissues?
7. The amino acid sequence of the ?-globin subunits of Hb-B1 and Hb-B2 is different at four positions:  the 62nd, 72nd, 128th, and 135th amino acids differ between Hb-B1 and Hb-B2.  All the other amino acids are the same between the two types of Hb.  Explain how a difference in amino acid sequence could change function of the entire Hb molecule.
8. Use Figure 34.25a in Campbell Biology in Focus to estimate P50 of adult human Hb.  Notice the units on this graph.  Determine whether a conversion factor is necessary to convert to the same units as your deer mouse graph.  Which type of Hb has a higher affinity for O2, deer mouse Hb-B1 or human Hb?

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