I need help with questions 1, 2, and 3. I Asprin is a weak acid (pKa-35) that is
ID: 142185 • Letter: I
Question
I need help with questions 1, 2, and 3.
Explanation / Answer
As Aspirin is a weak acid with a 3.5 pKa, is absorbed into the blood through the cells lining the stomach and the small intestine but with a pKa of 3.5, aspirin is in its protonated (neutral) form at pH below 2.5. At higher pH, it becomes increasingly deprotonated (anionic). Thus, aspirin is better absorbed in the more acidic environment of the stomach, because absorption requires passage through the plasma membrane, the rate of which is determined by the polarity of the molecule: charged and highly polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly. in the intestine, it becomes anionic means charged, so absorption occurs but slowly, though it has maximum surface area for the absorption.
2. It can be dissolved in water or organic solvents, embedded in micelles and in membranes. Melittin is a small peptide with no disulfide bridge; the N-terminal part of the molecule is predominantly hydrophobic and the C-terminal part is hydrophilic and strongly basic. In water, it forms a tetramer but it also can spontaneously integrate itself into cell membranes. In water, melittin can exist as a monomer or, at high concentration or high ionic strength, as a tetramer. In the monomeric form, the conformation is disordered, whereas in the tetrameric form it is predominantly a-helical.
It is a small linear peptide composed of 26 amino acid residues (NH2-GIGAVLKVLTTGLPALISWIKRKRQQ-CONH2) and is known to have a powerful hemolytic activity. It is a cationic peptide in which the amino terminal is composed predominantly of hydrophobic amino acids (residues 1–20), whereas the carboxy terminal end has a stretch of predominantly hydrophilic amino acids (residues 21–26) that give rise to its amphiphilic character. This amphiphilic property of melittin makes it water soluble and yet it spontaneously associates with natural and artificial membranes. Such a sequence of amino acids, coupled with its amphiphilic nature, is characteristic of many membrane-bound peptides and putative transmembrane helices of membrane proteins. This is the reason that the entire polypeptide can reside in the membrane.
3. a. The pi value for all animal insulins would be similar to human insulin except for chicken and duck. This is because, amino acid changes all involved neutral amino acids. Chicken insulin would be more basic whereas duck would be more acidic. The pI value of one protein is differs from another protein, because they vary in their amino acid content. For example, each amino acid has its own and unique pH. For each amino acid, there is a specific pH at which the concentration of the zwitterionic form reaches its maximum value. This pH is called the isoelectric point (pI), and each amino acid has its own unique pI.
b.