Hemoglobin Physiology and Gas Binding

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Questions and Answers

What is the physiological significance of the Bohr effect on hemoglobin's affinity for oxygen?

It alters hemoglobin's structure to bind more oxygen under normal conditions.

It increases hemoglobin's affinity in low pH environments.

It decreases hemoglobin's affinity in response to high concentrations of protons. (correct)

It eliminates the effects of BPG on hemoglobin's oxygen binding.

How does carbon monoxide (CO) interact with hemoglobin compared to oxygen?

CO binds to hemoglobin more weakly than O2.

CO is preferentially released from hemoglobin in acidic environments.

CO causes a conformational change that enhances hemoglobin's affinity for oxygen.

CO competes with oxygen but binds more effectively due to structural differences in hemoglobin. (correct)

What role does 2,3-bisphosphoglycerate (BPG) play in hemoglobin's function?

It promotes the formation of hemoglobin F over hemoglobin A.

It decreases hemoglobin's oxygen affinity, facilitating oxygen release. (correct)

It maintains a high pH in the blood to support oxygen binding.

It increases the binding affinity of hemoglobin for oxygen.

How does the presence of the gamma subunit in fetal hemoglobin (HbF) affect its affinity for oxygen?

HbF exhibits a higher affinity for oxygen due to reduced interactions with BPG. Signup and view all the answers

What is the relationship between hemoglobin and acid-base homeostasis?

Hemoglobin acts as a buffer by binding protons, contributing to pH stability. Signup and view all the answers

What is the genetic basis of thalassemias?

Thalassemias result from deletions or mutations in alpha or beta globin genes resulting in reduced or absent hemoglobin production. Signup and view all the answers

What percentage of sequence homology exists between Mb and Hb?

17% Signup and view all the answers

Which of the following amino acids is conserved across species when comparing Mb and Hb?

Histidine Signup and view all the answers

What is the structural composition of myoglobin?

It contains 75% α-helices. Signup and view all the answers

Which gene is expressed only at the embryonic stage in the alpha gene cluster?

ζ Signup and view all the answers

Which of the following correctly describes the interaction of oxygen with hemoglobin?

Oxygen binds to the heme ferrous iron. Signup and view all the answers

What is the composition of fetal hemoglobin (HbF)?

α2γ2 Signup and view all the answers

Which of these statements about the α and β gene families is correct?

Both gene families consist of gene clusters. Signup and view all the answers

What distinguishes the structure of hemoglobin from myoglobin?

Hemoglobin has a quaternary structure with four polypeptide chains. Signup and view all the answers

Which form of hemoglobin contains the δ gene?

HbA2 Signup and view all the answers

Which chains are included in normal adult hemoglobin (HbA1)?

α2β2 Signup and view all the answers

How many distinct α-helical regions are present in globin proteins like myoglobin and hemoglobin?

Eight Signup and view all the answers

What characteristic distinguishes the β family of hemoglobin subunits?

Has higher affinity for O2 than the α family Signup and view all the answers

How many conserved residues are there when comparing Mb and Hb across species?

Nine Signup and view all the answers

What role do the histidine residues play in hemoglobin's structure?

They interact with oxygen at the active site. Signup and view all the answers

What drives and stabilizes the structure of myoglobin?

Hydrophobic forces. Signup and view all the answers

Which of the following statements about hemoglobin is false?

Hemoglobin structure is identical to that of myoglobin. Signup and view all the answers

What is the primary role of BPG in hemoglobin function?

To stabilize the T-form of hemoglobin Signup and view all the answers

How does the absence of BPG influence the oxygen saturation curve of hemoglobin?

It makes the curve hyperbolic and similar to myoglobin Signup and view all the answers

Which amino acid residues does BPG interact with within the hemoglobin molecule?

Lysine and histidine Signup and view all the answers

What physiological adaptation occurs in response to high altitude concerning BPG?

BPG concentration increases to facilitate oxygen release Signup and view all the answers

What effect does BPG have on hemoglobin's affinity for oxygen?

BPG decreases oxygen affinity, aiding in oxygen release Signup and view all the answers

What is the mechanism by which BPG affects oxygen binding cooperativity in hemoglobin?

By stabilizing the T-form of hemoglobin and reducing O2 affinity Signup and view all the answers

What is the consequence of the reduced production of α globin chains in adults?

Excess of β chains Signup and view all the answers

Which genotype corresponds to the asymptomatic (silent carrier) phenotype?

α1α2O/α1α2 Signup and view all the answers

In which condition is HbH disease primarily characterized by?

Unstable tetramers of β chains Signup and view all the answers

What is the expected phenotype when all four α loci are affected?

Hydrops fetalis; fatal in utero Signup and view all the answers

Which of the following genotypes represents the α thalassemia Minor phenotype?

α1α2/α1α2 or O O Signup and view all the answers

What is a characteristic feature of the α thalassemias when only one locus is affected?

Minimal biological effect Signup and view all the answers

Hb Bart's is primarily formed from which chains, and when is it most prevalent?

γ chains; at birth then declines Signup and view all the answers

The severity of α thalassemias is correlated with what factor?

Number of affected α globin loci Signup and view all the answers

Study Notes

Physiological Significance of Protons, CO2, BPG, and HbF

The Bohr Effect describes how protons (H+) and carbon dioxide (CO2) decrease hemoglobin's (Hb) affinity for oxygen (O2) by stabilizing the T (tense) state.
Increased CO2 levels lead to more H+ ions, promoting oxygen release in tissues where it is most needed.
BPG (2,3-bisphosphoglycerate) lowers O2 affinity by binding to hemoglobin, facilitating O2 release, especially under conditions of hypoxia or high altitude.
Fetal hemoglobin (HbF) with γ-subunits has a higher affinity for O2 than adult Hb (α2β2), favoring oxygen transfer from maternal blood to fetus.

Carbon Monoxide (CO) Binding

Carbon monoxide competes with oxygen for binding sites on hemoglobin due to its higher affinity for heme iron.
The presence of distal histidine in hemoglobin reduces this affinity, making it less effective for CO binding compared to O2.
CO binding inhibits oxygen release, leading to potential tissue hypoxia.

Hemoglobin and Acid-Base Homeostasis

Hemoglobin acts as a buffer in the blood, binding excess H+ ions and CO2, which helps maintain pH levels in the body.
The interaction between deoxygenated hemoglobin and protons promotes the release of O2, supporting cellular respiration and acid-base balance.

Molecular Genetic Basis of Thalassemias

Thalassemias are genetic disorders caused by mutations in globin gene clusters, leading to reduced production of either α or β globin chains.
The severity of α-thalassemia correlates with the number of affected α globin loci; more loci affected results in more severe disease manifestations.
Genotype-phenotype relationships show that the degree of symptomatology differs greatly with variations in affected loci.
Excess β chains in α-thalassemia result in the formation of unstable tetramers (HbH), leading to altered oxygen dissociation properties.
In β-thalassemia, mutations reduce β chain production leading to α chain accumulation, causing ineffective erythropoiesis and anemia.

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Description

Explore the physiological significance of protons, carbon dioxide, and bisphosphoglycerate in hemoglobin function. Understand the Bohr Effect, the intricacies of oxygen release under different conditions, and the impact of carbon monoxide binding on hemoglobin. This quiz delves into the factors that influence oxygen affinity and transport in the body.