Hello guys, I just wanted some clarification of these question.
1. A sequence of amino acids in a certain protein is found to be -Ser-Pro-Gly-Gly-. The sequence is most probably part of a
1. a-helix
2.b-turn (b-bend)
3. parallel b-pleated sheet
4. a-sheet.
2. The pathological changes in sickle cell anemia are due to
a. loss of ability of the heme group to bind oxygen
b. decrease in the solubility of deoxyhemoglobin
c. increase in the solubility of oxyhemoglobin
d. dissociation of iron(II)ion from heme.
To answer the first question, we need to understand the different secondary structures of proteins. The four options mentioned are - a-helix, b-turn (b-bend), parallel b-pleated sheet, and a-sheet.
1. a-helix: An a-helix is a right-handed coiled structure with hydrogen bonds stabilizing it. It forms a compact structure.
2. b-turn (b-bend): A b-turn is a short segment of a protein that reverses the direction of the polypeptide chain. It is commonly found on the protein surface.
3. parallel b-pleated sheet: In parallel b-pleated sheets, the polypeptide chains run in the same direction, and adjacent chains are aligned in a parallel manner. Hydrogen bonds stabilize the structure.
4. a-sheet: An a-sheet consists of several polypeptide chains aligned side by side with inter-chain hydrogen bonding.
Now, let's analyze the given amino acid sequence (-Ser-Pro-Gly-Gly-). A key observation is the presence of glycine (Gly) at positions 3 and 4, which are adjacent. Glycine is a small amino acid with a flexible side chain. Such a repeated occurrence of glycine generally suggests the presence of a b-turn.
Therefore, the sequence is most likely part of a b-turn (b-bend).
Moving on to the second question regarding sickle cell anemia, we need to consider the specific pathological changes associated with the condition.
Sickle cell anemia is caused by a mutation in the hemoglobin gene, leading to the production of abnormal hemoglobin called hemoglobin S. The key pathological change in sickle cell anemia is the distorted shape (or "sickling") of red blood cells under certain conditions.
The distorted shape of red blood cells is primarily due to the polymerization of hemoglobin S when it becomes deoxygenated. This polymerization causes the red blood cells to form a sickle shape, leading to numerous complications.
From the given options, the most accurate choice is "b. decrease in the solubility of deoxyhemoglobin." This decrease in solubility promotes the polymerization of hemoglobin S and subsequent sickling of red blood cells, resulting in the pathophysiology of sickle cell anemia.
I hope this clears up any confusion you had!