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Questions and Answers
What is the primary non-protein component of hemoglobin?
What is the primary non-protein component of hemoglobin?
Which type of hemoglobin cannot form a reversible bond with oxygen?
Which type of hemoglobin cannot form a reversible bond with oxygen?
What is the structural arrangement of pyrrole rings in the tetrapyrrole unit of heme?
What is the structural arrangement of pyrrole rings in the tetrapyrrole unit of heme?
Which derivative of hemoglobin has the highest affinity for carbon monoxide?
Which derivative of hemoglobin has the highest affinity for carbon monoxide?
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How many globin components are present in hemoglobin?
How many globin components are present in hemoglobin?
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In the process of releasing oxygen, oxyhemoglobin is converted to which form?
In the process of releasing oxygen, oxyhemoglobin is converted to which form?
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What is the molecular weight of hemoglobin approximately?
What is the molecular weight of hemoglobin approximately?
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Which bridge connects the pyrrole rings in the structure of heme?
Which bridge connects the pyrrole rings in the structure of heme?
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What is the primary structural characteristic that differentiates the α-chain from the β-chain in adult hemoglobin?
What is the primary structural characteristic that differentiates the α-chain from the β-chain in adult hemoglobin?
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Which type of hemoglobin is primarily present at birth and later replaced by Hb A?
Which type of hemoglobin is primarily present at birth and later replaced by Hb A?
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What significant role does hemoglobin play in the human body beyond oxygen transport?
What significant role does hemoglobin play in the human body beyond oxygen transport?
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In the structure of adult hemoglobin, how is the heme-pocket of the β-subunit distinct compared to the α-subunit?
In the structure of adult hemoglobin, how is the heme-pocket of the β-subunit distinct compared to the α-subunit?
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What fraction of total hemoglobin is made up of Hb A in normal humans?
What fraction of total hemoglobin is made up of Hb A in normal humans?
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What is the composition of a typical adult hemoglobin molecule?
What is the composition of a typical adult hemoglobin molecule?
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What distinguishes Hb A1c from other forms of hemoglobin?
What distinguishes Hb A1c from other forms of hemoglobin?
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Which of the following best describes the quaternary structure of hemoglobin?
Which of the following best describes the quaternary structure of hemoglobin?
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What is the primary function of the heme group in hemoglobin?
What is the primary function of the heme group in hemoglobin?
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Which disorder is associated with a structural change in hemoglobin, leading to significant clinical consequences?
Which disorder is associated with a structural change in hemoglobin, leading to significant clinical consequences?
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In beta thalassemia major, what is a common clinical manifestation related to bone structure?
In beta thalassemia major, what is a common clinical manifestation related to bone structure?
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Which statement accurately describes the transition from Hb F to Hb A after birth?
Which statement accurately describes the transition from Hb F to Hb A after birth?
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Which of the following statements is true about the structure of the heme group?
Which of the following statements is true about the structure of the heme group?
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Which symptom is NOT typically associated with beta thalassemia major?
Which symptom is NOT typically associated with beta thalassemia major?
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What is the natural state of the iron atom in the heme group?
What is the natural state of the iron atom in the heme group?
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How does chronic anemia affect endocrine functions in individuals with beta thalassemia major?
How does chronic anemia affect endocrine functions in individuals with beta thalassemia major?
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Study Notes
Hemoglobin Structure and Types
- Red blood cells contain hundreds of thousands of hemoglobin molecules, responsible for transporting oxygen.
- Oxygen binds to heme, a component within the hemoglobin molecule.
Hemoglobin Structure
- Hemoglobin (Hb) is a spherical molecule comprising four peptide subunits (globins), forming a quaternary structure.
- Adult hemoglobin (Hb A) is a tetramer, composed of two alpha (α) and two beta (β) globins.
- Each globin subunit contains one heme group with a central iron (Fe²⁺) ion.
Heme Structure
- Heme is a Fe-porphyrin compound.
- Porphyrins are cyclic compounds formed by fusing four pyrrole rings linked by methenyl bridges (=CH-).
- The pyrrole rings are labeled I, II, III, and IV, and bridges as alpha, beta, gamma, and delta.
- The presence of an iron atom makes heme a ferroprotoporphyrin.
Hemoglobin Derivatives
- Hemoglobin readily reacts with other substances.
- Oxyhemoglobin: An unstable and reversible compound where iron remains in the ferrous (Fe²⁺) state.
- Reduced/Deoxygenated hemoglobin: Oxygen is released from oxyhemoglobin.
- Carbaminohemoglobin: Binds with carbon dioxide.
- Carboxyhemoglobin: Binds with carbon monoxide (CO); CO has a much higher affinity for hemoglobin than oxygen.
- Methemoglobin: Iron is oxidized to ferric (Fe³⁺), preventing the reversible binding of oxygen.
- Glycosylated hemoglobin (HbA1c): Glucose attaches to terminal valine in the beta (β) chains; elevated levels indicate diabetes mellitus.
Physiological Varieties of Hemoglobin
- Fetal hemoglobin (HbF): Found in fetal red blood cells, it has a higher affinity for oxygen than adult hemoglobin; it disappears within 2-3 months after birth
- Its globin part consists of two alpha (α) and two gamma (γ) polypeptide chains in place of two beta (β) chains.
Hemoglobin Functions
- Transport of Respiratory Gases: Carries oxygen from lungs to tissues, and carbon dioxide from tissues to lungs.
- Major Blood Buffer: Hemoglobin's histidine residues contribute substantially to blood pH regulation
- Other Functions: Changes in hemoglobin structure can lead to various disorders (e.g., sickle cell anemia, thalassemia, methemoglobinemia).
Hemoglobin Synthesis-Factors Controlling
- Role of Proteins: Amino acids from protein sources are required for globin synthesis. Low protein intake hinders globin regeneration
- Role of Iron: Essential for heme synthesis. Iron recycled from old red blood cells is also reused.
- Role of other Metals (e.g,, Copper): Required for proper iron absorption and mobilization.
Fate of Hemoglobin
- Hemoglobin is broken down, releasing globin and iron components.
- Release of amino acids for reuse and bilirubin that is metabolized. The Iron is stored as ferritin or transferred to the bone marrow for reuse.
Myoglobin
- Myoglobin (Mb) is a monomeric oxygen-binding hemoprotein found in heart and skeletal muscle, serving as an oxygen reservoir. It has a single polypeptide chain with a heme moiety.
Hemoglobin Structure-Quaternary Structure
- There are two alternate conformations of Hemoglobin's Quaternary Structure
- The T-State (Tense): Has low affinity for oxygen; deoxy state
- The R-State (Relaxed): Has higher affinity for oxygen; oxy state
- These conformations shift based on oxygen binding and allosteric factors.
Structure of Globin
- Globin is made of four polypeptide chains: two alpha (α) chains and two beta (β) chains
- Each alpha chain contains 141 amino acids, each beta chain contains 146 amino acids
- Normal adult hemoglobin A is written as α₂β₂.
Red Blood Cell (RBC) Lifespan
- The average lifespan of red blood cells is about 120 days.
- Conditions that reduce lifespan include hereditary and extracorpuscular defects, as well as deficits in red blood cell enzymes.
Organs Involved in Heme Synthesis
- The variable organs involved in heme synthesis include reticuloendothelial cells, typically found in various sites like the liver
Hemoglobin Levels
- Normal hemoglobin levels (g/dL): Male 14-18; Female 12-15.5
- Levels can vary based on age and physiological state (e.g., pregnancy).
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Description
Explore the fascinating world of hemoglobin in this quiz. Understand its unique structure, the role of heme, and differentiate between its various derivatives. Test your knowledge on how hemoglobin facilitates oxygen transport in the human body.
