Oxygen binding by hemoglobin - analytical assignment BIOL 1306: Cheek

Partial pressure

The contribution of each gas in the mixture

Identify 3 different units used to measure partial pressure.

1. mmHg

2. Pascal (Pa)

3. atm

Torr

• Unit of pressure = 133.322 Pa

• 1 atm = 760 torr

What is the PO2 of the atmosphere at sea level? Express in units of torr.

As oxygen is 21% of dry air, the inspired oxygen pressure is 0.21×760 mmHg = 21.3 kPa = 159.6 torr at sea level.

A solution of Hb is 98% saturated with O2 when the partial pressure of O2 is 100 mmHg. What is the partial pressure of O2 in units of kPa?

13.33 kPa (kPa = mmHg × 0.1333)

Which is the independent variable in this case?

Partial Pressure of O2 (PO2 torr)

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.

• Hb-B1 at 7

• Hb-B2 at 10.5

Respiratory pigment

A substance (such as hemoglobin or hemocyanin) with a molecule consisting of protein with a pigmented prosthetic group, involved in the physiological transport of oxygen or electrons.

Heme

An iron-containing compound of the porphyrin class that forms the nonprotein part of hemoglobin and some other biological molecules.

Name the respiratory pigment found in vertebrates. Identify the metal ion associated with the porphyrin rings of each respiratory pigment.

• Hemoglobin

• This porphyrin ring consists of four pyrrole molecules

  cyclically linked together (by methine bridges) with the iron ion bound in the center.

Name the respiratory pigment common in decapod crustaceans. Identify the metal ion associated with the porphyrin rings of each respiratory pigment.

• Hemocyain

• The copper atoms of hemocyanin are bound

  as prosthetic groups coordinated by histidine residues.

How many subunits does vertebrate Hb have and what are they named?

• 4 globular protein subunits.

  • All-α

  • All-β

  • α+β

  • α/β

To what part of the Hb molecule does O2 bind?

Iron ion

How many oxygen binding sites does each Hb molecule have?

4

If a solution contains 1 x 10^6 Hb molecules, how many O2 binding sites are available?

4 X (1 X 10^6) = 4 X 10^6 O2 binding sites.

If the solution of Hb is 50% saturated with O2, how many binding sites are occupied by O2?

2 x 10^6

If the Hb solution is 23% saturated with O2, how many binding sites are occupied by O2?

10^6

Define affinity of a molecule for a ligand.

The interaction of most ligands with their binding sites can be characterized in terms of a binding affinity. In general, high-affinity ligand binding results from greater intermolecular force between the ligand and its receptor

Which type of Hb has higher oxygen affinity?

Hb-B1 (affinity)

Which form of Hb would you expect to find in deer mice living at high altitude where the PO2 of the atmosphere is less?

Hb-B1 (altitude)

Which form of deer mouse Hb releases O2 more easily when blood circulates to body tissues?

Hb-B1

The amino acid sequence of the β-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.

Because different proteins differ from the sequence of amino acids

Use Figure 42.18 in Biological Sciences Freeman et al., 6th edition to estimate P50 of adult human Hb.

25 torr

Which type of Hb has a higher affinity for O2, deer mouse Hb-B1 or human Hb?

Deer mouse Hb-1

Notice the units on this graph. Determine whether a conversion factor is necessary to convert to the same units as your deer mouse graph

It’s not necessary