Answer :
1. The right answer is True.
Hemoglobin, commonly symbolized by Hb, sometimes Hgb, is an iron-containing metalloprotein, found mainly in the blood of vertebrates within their red blood cells, as well as in the tissues of certain invertebrates.
Hemoglobin has a quaternary structure characteristic of many globular subunit proteins. Most of its amino acid residues are involved in α helices interconnected by non-helical segments.
2. The right answer is False.
The helicoidal sections of hemoglobin are stabilized by hydrogen bonds which give the protein its characteristic three-dimensional structure, called globin folding, as it is also found in other globins with prosthetic hemic groups such as myoglobin8. This characteristic folding has a cavity in which is closely inserted a heme molecule constituting the prosthetic group of the protein. Hemoglobin therefore contains one molecule of heme per subunit.
3 The right answer is False.
The biosynthesis of hemoglobin involves a complex set of steps. Heme is the result of a series of reactions that start in the mitochondria and continue in the cytosol of immature erythrocytes, while the apoprotein is produced at the ribosomes of the cytosol (and not those of the endoplasmic reticulum). Hemoglobin production occurs in the early stages of erythropoiesis, from the proerythroblast to the reticulocyte stage in the bone marrow.
4. The right answer is False.
Mutations on the hemoglobin genes can lead to hemoglobin variants. Most of these variants are functional and have no effect on health. Some mutations in hemoglobin, by contrast, are likely to cause genetic diseases called hemoglobinopathies.
Sickle cell disease is due to the substitution of a single amino acid residue for the β-chain of hemoglobin (without change in the alpha chain). This genetic mutation - replacement of glutamate in position 6 by a valine, giving hemoglobin S - promotes, under certain conditions, the appearance of rigid red cells of elongated shape, called sickle or acanthus leaf, likely to induce three broad categories of clinical manifestations.
- The statement “Hemoglobin has quaternary structure” is true.
- “Individual alpha-helices found in hemoglobin are stabilized by ionic bonds” is false.
- “Hemoglobin would be synthesized by a ribosome on the rough ER” this is a false statement.
- “A DNA mutation that affects the primary structure of the alpha-globin protein sub-unit would also affect the primary structure of the beta-globin protein sub-unit.” is not true.
Further Explanation:
A polypeptide chain leads to formation of proteins. There are exceptions to proteins; some of them are formed by the association of more than one polypeptide chain (sub-units). These proteins are termed to be as Quaternary proteins.
Depending upon the number of protein chain subunits proteins can be of following types;
- Dimers
- Tetramers
- Hexamers
Hemoglobin is one such quaternary protein which is formed by as of polypeptide chains association. The polypeptide chains found in hemoglobin are;
- Two alpha chains.
- Two beta chains.
The 3D structure of the molecule is as the result of the hydrogen bond interactions. This interactions gives the molecule it characteristic shape and helps it to carry out it functions effectively.
Formation of hemoglobin occurs differently depending on the components. The hemoglobin molecule has two components that are heme and globin.
The Heme part is formed at following location;
- Mitochondria
- Cytosol of immature erythrocytes.
While, the ‘globin’ part is synthesized by the ribosomes, in the cytosol of the cell. The change or mutation in one of the chain won’t affect the other chain but surely the overall functions and physicality will be altered. For example, the replacement of glutamic acid codon (GAG) to a valine codon (GTG) can lead to sickle cell anemia.
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Answer Details:
Grade: High School
Subject: Biology
Topic: Hemoglobin
Keywords:
Hemoglobin, quaternary structure, rough ER, myoglobin, structure, globin, folding, hydrogen bond, heme, variant, oxygen, erythrocytes, beta, alpha.
