Chapter 7. Hemoglobin: Portrait of a Protein in Action

Question 1

An organic constituent of the heme prosthetic group; consists of four pyrrole rings joined by methylene bridges and contains various side chains.

Answer 1

Protoporphyrin

Question 2

A histidine in globins that forms a hydrogen bond to the bound oxygen that helps to prevent the release of superoxide anion.

Answer 2

Distal histidine

Question 3

An allosteric effector of hemoglobin that decreases the affinity of hemoglobin for oxygen.

Answer 3

2,3-bisphosphoglycerate

Question 4

A member of the globin family expressed throughout the body.

Answer 4

Cytoglobin

Question 5

CO; A colorless, odorless gas that binds to hemoglobin at the same site as oxygen and thereby prevents oxygen binding.

Answer 5

Carbon monoxide

Question 6

An enzyme that catalyzes the reaction of carbon dioxide with water to form carbonic acid.

Answer 6

Carbonic anhydrase

Question 7

Hemoglobin that consists of two a chains and two a chains that has a higher affinity for oxygen than hemoglobin A. This difference in affinity allows the transfer of oxygen from the mother to the fetus.

Answer 7

Fetal hemoglobin

Question 8

A model explaining the kinetics of allosteric enzymes in which the transitions of all of the active sites between the T state and the R state occur simultaneously.

Answer 8

Concerted model (MWC model)

Question 9

A property of allosteric proteins wherein the reactions at different sites are not independent of one another.

Answer 9

Cooperative binding

Question 10

An organic compound the results from the reaction of carbon dioxide with the amino groups in proteins. Carbamate formation in hemoglobin reduces oxygen affinity of hemoglobin

Answer 10

Carbamate

Question 11

The observation made by Christian Bohr that H+ and CO2 promote the release of oxygen from oxyhemoglobin.

Answer 11

Bohr effect

Question 12

A complex of carbon monoxide and hemoglobin that does not bind oxygen.

Answer 12

Carboxyhemoglobin

Question 13

The prosthetic group of myoglobin and hemoglobin as well as other proteins; consists of an organic constituent, protoporphyrin, and an iron atom.

Answer 13

Heme

Question 14

A brain-imaging technique that takes advantage of (1) the fact that magnetic properties of oxyhemoglobin and deoxyhemoglobin are different and can thus be distinguished and (2) the fact that, when a specific part of the brain is active, blood vessels relax and allow more blood flow. Thus, a more active part of the brain will be richer in oxyhemoglobin.

Answer 14

Functional magnetic resonance imaging (fMRI)

Question 15

The fraction of possible binding sites of a biomolecule that are occupied.

Answer 15

Fractional saturation

Question 16

A plot of the fractional saturation of oxygen binding proteins versus the concentration of oxygen.

Answer 16

Oxygen-binding curve

Question 17

Myoglobin in which the iron of the heme is in the ferric state (Fe&sup3+;) and thus cannot bind oxygen.

Answer 17

Metmyoglobin

Question 18

The fraction of the total pressure of a mixture of gases that is due to one component of the mixture.

Answer 18

Partial pressure

Question 19

One of the protein subunits of hemoglobin. Hemoglobin is composed of two α chains and two β chains.

Answer 19

β chain

Question 20

A folding structure of a polypeptide chain, exemplified by myoglobin and hemoglobin subunits, that creates an environment for a heme group to reversibly bind oxygen.

Answer 20

Globin fold

Question 21

A reactive oxygen species that can damage many biological materials.

Answer 21

Superoxide anion (O2-)

Question 22

One of the protein subunits of hemoglobin. Hemoglobin is composed of two α chains and two β chains.

Answer 22

α chain

Question 23

A model for explaining allosteric enzymes in which the binding of one substrate influences the substrate affinity of neighboring active sites without necessarily inducing a transition encompassing the entire enzyme.

Answer 23

Sequential model

Question 24

Activity curves, such as for oxygen binding or enzyme activity, that show low activity with respect to the x-axis initially and then increase rapidly, thereby generating an “S” shaped curve.

Answer 24

Sigmoid

Question 25

Hemoglobin, which forms in the absence of the α chain, that consists only β chains. Hemoglobin H binds oxygen with high affinity and displays no cooperativity.

Answer 25

Hemoglobin H

Question 26

The less active state of allosteric proteins, which is in equilibrium with the more active R-state.

Answer 26

T state

Question 27

a mutant form of hemoglobin and the cause of sickle cell anemia that aggregates when the oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes that impede blood flow in capillaries.

Answer 27

Hemoglobin S

Question 28

The more active state of allosteric proteins, which is in equilibrium with the less active T-state.

Answer 28

R state

Question 29

Anemia caused by a mutation in hemoglobin that promotes aggregation of the hemoglobin when oxygen concentration is low, which in turn causes the red blood cells to form sickle shapes. Such deformed cells to not remain in circulation, thus accounting for the anemia.

Answer 29

Sickle-cell anemia

Question 30

A disease carried by a mosquito parasite, Plasmodium falciparum, that lives within red blood cells at one stage in its life cycle. The presence of one allele for hemoglobin S confers resistance to malaria.

Answer 30

Malaria

Question 31

Genetic disorders characterized by the defective synthesis of one or more hemoglobin chains.

Answer 31

Thalassemia

Question 32

A severe form of anemia that results from the total absence of the β chains of hemoglobin.

Answer 32

Thalassemia major (Cooley anemia)

Question 33

A member of the globin family expressed primarily in the brain, where it appears to protect against hypoxia (insufficient oxygen).

Answer 33

Neuroglobin

Question 34

A plot of log(Y/1-Y) versus log(pO2), where Y is fractional saturation and pO2 is partial pressure of oxygen, that can be used to determine the degree of cooperativity of oxygen binding.

Answer 34

Hill plot

Question 35

The slope of the line generated by a Hill plot. The Hill coefficient is a measure of cooperativity in ligand binding.

Answer 35

Hill coefficient

Question 36

This histidine in myoglobin and hemoglobin that coordinates to the iron in porphyrin through its imidazole ring.

Answer 36

proximal histidine

Question 37

Individuals with one copy of the HbA gene and one copy of the HbS gene are said to have this trait because they can pass the HbS gene to their offspring.

Answer 37

sickle-cell trait

Question 38

A red blood cell protein that binds to the α chain of hemoglobin to ensure the proper folding of the a chain. AHSP is subsequently displaced by the β chain.

Answer 38

α-hemoglobin stabilizing protein (AHSP)