Structure and Function of Myoglobin and Hemoglobin

Questions and Answers

What are the contents of plasma?

Water, proteins, nutrients, hormones, etc.

What are the physiological roles of hemoglobin?

Hb binds O2 in the alveoli of the lungs and delivers O2 to tissues. It also helps maintain acid-base balance.

What is partial pressure?

The partial pressure of a gas is equal to the atmospheric pressure times the fraction of the atmosphere that is composed of that gas.

What is myoglobin and what is its function?

Myoglobin is synthesized inside muscle cells to store oxygen for high metabolic demand. Signup and view all the answers

How does myoglobin vary with skeletal muscle fiber type?

Myoglobin content varies with skeletal muscle fiber type: IA > IIA > IIB. Signup and view all the answers

Describe the features of the structure of myoglobin.

Single polypeptide chain; ~80% alpha-helical; closely-packed tertiary structure; single heme molecule bound; binds one O2 molecule. Signup and view all the answers

Describe the features of the structure of hemoglobin.

4 polypeptide chains - 2 alpha chains and 2 beta chains; each chain folds similar to myoglobin; binds up to 4 O2. Signup and view all the answers

What is the structure of HbA?

HbA = alpha2beta2 = 97 - 98.5% of total Hb in adults. Signup and view all the answers

What is the structure of HbA2?

HbA2 = alpha2delta2 = 1.5 - 3% of total Hb in adults. Signup and view all the answers

What is the structure of HbF?

HbF = alpha2gamma2; it is fetal hemoglobin that is major from ~1 month gestation until near birth. Signup and view all the answers

What is the structure of Hbepsilon?

= zeta2epsilon2 or alpha2epsilon2 or zeta2gamma2; embryonic hemoglobin from ~1 week post-conception until birth. Signup and view all the answers

What is thalassemia?

Thalassemias are an imbalance in globin chain synthesis. Signup and view all the answers

What are the causes of thalassemia?

Causes can include gene deletion, mutations affecting gene regulation or splicing. Signup and view all the answers

What does the alpha^0 or beta^0 classification mean?

No synthesis of a particular type of globin chain. Signup and view all the answers

What does the alpha^+ or beta^+ classification mean?

<ul> <li>or ++ reduced level of a particular type of globin chain.</li> </ul> Signup and view all the answers

What gene is deleted in beta-thalassemia minor?

1beta. Signup and view all the answers

What gene is deleted in beta-thalassemia major?

2beta. Signup and view all the answers

What gene is deleted in Cooley anemia?

2beta. Signup and view all the answers

What gene is deleted in the thalassemia that has no symptoms/silent carrier?

1alpha. Signup and view all the answers

What gene is deleted in the alpha-thalassemia trait?

2alpha. Signup and view all the answers

What gene is deleted in HbH disease?

3alpha. Signup and view all the answers

What gene is deleted in HbBart's disease?

4alpha. Signup and view all the answers

What gene is deleted in hydrops fetalis?

4alpha. Signup and view all the answers

Deletion of 1beta results in what type of thalassemia?

Beta-thalassemia minor. Signup and view all the answers

Deletion of 2beta results in what type of thalassemia?

Beta-thalassemia major/Cooley's anemia. Signup and view all the answers

Deletion of 1alpha results in what type of thalassemia?

Usually no symptoms; silent carrier. Signup and view all the answers

Deletion of 2alpha results in what type of thalassemia?

Alpha-thalassemia trait. Signup and view all the answers

Deletion of 3 alpha results in what type of thalassemia?

HbH disease (named after beta4 tetramer formed here). Signup and view all the answers

Deletion of 4alpha results in what type of thalassemia?

HbBart's disease or hydrops fetalis (Hb Bart's is gamma4 tetramer). Signup and view all the answers

Study Notes

Plasma Contents

Composed of water, proteins, nutrients, hormones.

Physiological Roles of Hemoglobin

Binds O2 in lung alveoli and delivers O2 to body tissues.
Maintains acid-base balance by binding CO2 and releasing it in the lungs.
Functions depend on partial pressure gradients of O2 and CO2.

Partial Pressure Definition

Equal to atmospheric pressure multiplied by the gas fraction.
Differences in partial pressures in lungs, tissues, and blood drive gas exchange.

Myoglobin

Synthesized in muscle cells to store oxygen.
Supports high metabolic demand during activity.

Myoglobin Variability in Muscle Fibers

Myoglobin content hierarchy: Type IA > Type IIA > Type IIB.

Myoglobin Structure

Made up of a single polypeptide chain.
Approximately 80% alpha-helix, with a compact tertiary structure.
Contains a single covalently bound heme molecule, capable of binding one O2.

Hemoglobin Structure

Composed of four polypeptide chains: two alpha and two beta.
Each chain is structured similarly to myoglobin with a heme molecule.
Capable of binding up to four O2 molecules.
Strong hydrophobic interactions between alpha1 & beta1 and alpha2 & beta2.
Weaker polar interactions between heterodimers alpha1beta2 and alpha2beta2.

Hemoglobin Variants

HbA: alpha2beta2, constitutes 97-98.5% of total hemoglobin in adults; glycosylation indicates chronic elevated blood sugar.
HbA2: alpha2delta2, accounts for 1.5-3% of total hemoglobin in adults.
HbF: alpha2gamma2, dominates from around one month gestation until just before birth; about 40% at birth.
HbEpsilon: zeta2epsilon2 or alpha2epsilon2 or zeta2gamma2, present from about one week post-conception until birth.

Thalassemia

A disorder characterized by an imbalance in globin chain synthesis.

Causes of Thalassemia

Results from gene deletion, mutations affecting gene regulation or splicing.
Unstable hemoglobins can lead to thalassemia-like symptoms.

Thalassemia Classifications

Alpha^0 or Beta^0: indicates no synthesis of a specific globin chain.
Alpha^+ or Beta^+: indicates a reduced level of a particular globin chain.

Gene Deletions in Thalassemia

Beta-thalassemia minor: deletion of 1 beta chain.
Beta-thalassemia major (Cooley anemia): deletion of 2 beta chains.
Silent carrier: deletion of 1 alpha chain, usually asymptomatic.
Alpha-thalassemia trait: deletion of 2 alpha chains.
HbH disease: deletion of 3 alpha chains, leads to a tetramer formation (beta4).
HbBart's disease and hydrops fetalis: deletion of all 4 alpha chains, forms gamma4 tetramers.

Thalassemia Outcomes

Deletion of 1 beta results in beta-thalassemia minor.
Deletion of 2 beta results in beta-thalassemia major or Cooley's anemia.
Deletion of 1 alpha typically presents no symptoms (silent carrier).
Deletion of 2 alpha results in alpha-thalassemia trait.
Deletion of 3 alpha leads to HbH disease.
Deletion of 4 alpha results in HbBart's disease or hydrops fetalis.

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Description

This quiz explores the structure and function of myoglobin and hemoglobin in the human body. It includes essential information about plasma contents and the physiological roles of hemoglobin, providing a comprehensive review of their importance in oxygen transport and acid-base balance.