- Hemoglobin (Hb) transports CO2 in venous blood as carbamates. The following statements refer to the formation of these carbamates:
A. CO2 interacts with amino terminal nitrogens of Hb polypeptide chains
B. CO2 interacts with carboxyl terminal carbons of Hb polypeptide chains
C. Carbamates helps formation of salt bridges between α and β chains of Hb
D. Carbamates helps formation of disulfide bridges between α and β chains of Hb
Which one of the following option is a combination of correct statements:
(1) A and C (2) B and D
(3) B and C (4) A and D
Introduction
Hemoglobin (Hb) transports carbon dioxide (CO2) in venous blood primarily by forming carbamates. This process involves CO2 binding chemically to hemoglobin’s amino groups, facilitating efficient CO2 transport from tissues to lungs.
Key Facts About Carbamate Formation on Hemoglobin
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CO2 binds to amino terminal nitrogens of the globin polypeptide chains (the free NH2 groups on α and β chains).
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This reaction forms carbaminohemoglobin, a compound with CO2 chemically attached to hemoglobin.
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Carbamate formation helps stabilize the T (tense) form of hemoglobin, favoring oxygen release (Bohr effect).
Structural Role of Carbamates
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The carbamate group aids in the formation of salt bridges between α and β chains of hemoglobin.
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These salt bridges stabilize the deoxyhemoglobin form, enhancing CO2 uptake and oxygen unloading.
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Carbamate groups do not form disulfide bridges (which involve sulfur atoms in cysteine residues).
Evaluating the Statements
Statement Correctness Explanation A. CO2 interacts with amino terminal nitrogens of Hb polypeptide chains Correct CO2 binds to free NH2 groups forming carbamates B. CO2 interacts with carboxyl terminal carbons of Hb polypeptide chains Incorrect CO2 does not bind to carboxyl terminals C. Carbamates help formation of salt bridges between α and β chains of Hb Correct Salt bridges stabilize the T form of Hb D. Carbamates help formation of disulfide bridges between α and β chains of Hb Incorrect Carbamates are unrelated to disulfide bond formation
Correct Combination
The correct combination of statements is:
(1) A and C
Summary
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CO2 binds to amino terminals (NH2) of globin chains forming carbamates.
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Carbamates help form salt bridges stabilizing deoxyhemoglobin.
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No involvement of carboxyl terminals or disulfide bridges in carbamate formation.
This chemical interaction facilitates CO2 transport and release in the lungs, integral to respiratory gas exchange.
Conclusion
The combination of correct statements about hemoglobin carbamate formation is:
(1) A and C
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