Oxygen binding by hemoglobin - analytical assignment BIO 1361: Cheek

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?

13.33 kPa (kPa = mmHg × 0.1333)

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.

Hemoglobin is found in red blood cells which are normally bi - con - cave in shape. If hemoglobin has a difference in amino acid sequence it will turn into a gel like substance altering the shape of some red blood cells. These cells can then get stuck in the capillaries, blocking some of the of the oxygen getting around the body.

Define affinity of a molecule for a ligand.

Ligand binding to a receptor protein alters the chemical conformation by affecting the three-dimensional shape orientation. The conformation of a receptor protein composes the functional state. Ligands include substrates, inhibitors, activators, and neurotransmitters. The rate of binding is called affinity, and this measurement typifies a tendency or strength of the effect. Binding affinity is actualized not only by host-guest interactions, but also by solvent effects that can play a dominant, stericrole which drives non-covalent binding in solution.

11. Which is the independent variable in this case?

PO2 (torr) %sat Hb-B1 %sat Hb-B2 0 0 0 6 39 -- 6.5 -- 24 7 50 -- 9.0 62 40 12 72 60 15 -- 70 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.

PO2 (torr) %sat Hb-B1 %sat Hb-B2 0 0 0 6 39 -- 6.5 -- 24 7 50 -- 9.0 62 40 12 72 60 15 -- 70 a. Hb B1 - 7 b. Hb B2 - 10.5

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

PO2 (torr) %sat Hb-B1 %sat Hb-B2 0 0 0 6 39 -- 6.5 -- 24 7 50 -- 9.0 62 40 12 72 60 15 -- 70 Hb B1

Using your answer to question 12, which type of Hb has higher oxygen affinity?

PO2 (torr) %sat Hb-B1 %sat Hb-B2 0 0 0 6 39 -- 6.5 -- 24 7 50 -- 9.0 62 40 12 72 60 15 -- 70 a. Hb B1

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

PO2 (torr) %sat Hb-B1 %sat Hb-B2 0 0 0 6 39 -- 6.5 -- 24 7 50 -- 9.0 62 40 12 72 60 15 -- 70 a. Hb B2

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

PO2 at sea level = 760 mmHg x .21 = 159.6 mmHG or 159.6 torr

To what part of the Hb molecule does O2 bind? How many oxygen binding sites does each Hb molecule have?

The iron is the site of oxygen binding; each iron can bind one O2 molecule thus each hemoglobin molecule is capable of binding a total to four (4) O2 molecules.

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?

a. 1 X 10^6 = 4 X 10^6 O2 binding sites. b. Half of the sites are occupied by O2. One fourth sites are occupied.

Use Figure 42.18 in Biological Sciences Freeman et al., 6th edition 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?

a. No conversion needed torr = mmHg b. Deer mouse Hb has a higher affinity to PO2 than human Hb

respiratory pigment

a. Respiratory pigment-Any of the oxygen-carrying substances in the blood and tissues, such as hemoglobin and myoglobin. It is a molecule, such as hemoglobin in humans and other vertebrates, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, haemocyanin, haemerythrinand chlorocruorin. Hemoglobin is bright red when oxygenated, and dark red(purplish) when deoxygenated, oxygenated haemocyanin is blue in color, deoxygenated it is almost colorless. Oxygenated chlorocruorin turns from green to red, whereas oxygenated haemerythrin is a violet to pink colour and colorless when deoxygenated. Any of various colored conjugated proteins, such as hemoglobin, occur in living organisms and function in oxygen transfer in cellular respiration.

partial pressure

a. The pressure exerted by a single component of a mixture of gases, commonly expressed in mm Hg or torr; for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. Formerly, symbolized by p, followed by the chemical symbol in capital letters (e.g., pCO2, pO2); now, in respiratory physiology, P, followed by subscripts denoting location and/or chemical species (e.g., PCO2, PO2, PaCO2).

torr

a. The torr (symbol: Torr) is a traditional unit of pressure, now defined as exactly 1 atm = 760 of a standard atmosphere, which in turn is defined as exactly 101325 pascals. Thus one torr is exactly 101325/760? 133.3 pascals. b. Historically, one torr was intended to be the same as one "millimeter of mercury". However, subsequent redefinitions of the two units made them slightly different (by less than0.000015%). The torr is not part of the International System of Units (SI), but it is often combined with the metric prefix milli to name one millitorr(mTorr) or 0.001 Torr.

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 pigment.

a. Vertebrates- hemoglobin- Fe(Iron) b. Decapod and crustaceans- hemocyanin - Cu (Copper) c. Hemoglobin - Iron Fe2+, has 4 protein subunits and single hemoglobin molecule binds up to 4 oxygen molecules. Hemocyanin - copper Cu2+ All have high affinity for oxygen, and binding of oxygen is non-covalent and reversible.

heme

b. Heme-The deep red, nonprotein, iron-containing component of hemoglobin that carries oxygen. Heme is a porphyrin with an iron atom at its center. One of the free valence electrons of the iron atom of heme is bound to the hemoglobin molecule, while the other is available for binding to an oxygen atom. A hemoglobin molecule contains four hemes. Chemical formula: C34H32FeN4O4. i. A small molecule that binds to each of the four polypeptides in hemoglobin; contains an iron ion that can bind oxygen.

Identify 3 different units used to measure partial pressure.

i. mmHg ii. torr iii. atm

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

the most common hemoglobin type is a tetramer (which contains 4 subunit proteins) called hemoglobin A, consisting of two alpha and two beta subunits non-covalently bound, each made of 141 and 146 amino acid residues, respectively.