Sally identified a new protein called nueolio that was absorbed from the circula

Question

Sally identified a new protein called nueolio that was absorbed from the circulatory system into cells of the liver. Initial analysis of the amino acid structure of Nueolio predicted that it would have charged residues when dissolved in a solution of PH 7.3.

a) Sally predicted Nuelolio was absorbed by simple diffusion into liver cells. Do you agree with her hyptheis? why or why not?

b) Further analysis of Nueolio determined the protein had an average concentration of 12.3 picomolar in the circulatory system and 4.5 picomolar in liver cells. Based on this new information, how do you hypthesize that Nueolio moves into the liver cells and why?

Explanation / Answer

Peptides and proteins are polymers made of amino acids linked together by amide bonds. The repeating units in a protein are called amino acid residues. Amino acid polymers can be composed of any number of monomers. A dipeptide contains two amino acid residues, a tripeptide contains three, an oligopeptide contains three to 10, and a polypeptide contains many amino acid residues. Proteins are naturally occurring polypeptides that are made up of 40 to 4000 amino acid residues. From the structure of an amino acid, we can see that it's name is not very precise. The compounds commonly called amino acids are more precisely called aminocarboxylic acids.

The internal composition of the cell is maintained because the plasma membrane is selectively permeable to small molecules. Most biological molecules are unable to diffuse through the phospholipid bilayer, so the plasma membrane forms a barrier that blocks the free exchange of molecules between the cytoplasm and the external environment of the cell. Specific transport proteins (carrier proteins and channel proteins) then mediate the selective passage of small molecules across the membrane, allowing the cell to control the composition of its cytoplasm.

Passive diffusion is thus a nonselective process by which any molecule able to dissolve in the phospholipid bilayer is able to cross the plasma membrane and equilibrate between the inside and outside of the cell. Importantly, only small, relatively hydrophobic molecules are able to diffuse across a phospholipid bilayer at significant rates. Thus, gases (such as O2 and CO2), hydrophobic molecules (such as benzene), and small polar but uncharged molecules (such as H2O and ethanol) are able to diffuse across the plasma membrane.

Other biological molecules, however, are unable to dissolve in the hydrophobic interior of the phospholipid bilayer. Consequently, larger uncharged polar molecules such as glucose are unable to cross the plasma membrane by passive diffusion, as are charged molecules of any size (including small ions such as H+, Na+, K+, and Cl-). The passage of these molecules across the membrane instead requires the activity of specific transport and channel proteins, which therefore control the traffic of most biological molecules into and out of the cell. thus it is impossible for the amino acid to diffuse into liver cells unaided.

If Sally's amino acid NUEOLIO could have been a cell-penetrating peptide then yes it can diffuse due to its modification. these CPPs are of different sizes, amino acid sequences, and charges but all CPPs have one distinct characteristic, which is the ability to translocate into the plasma membrane and facilitate the delivery of various molecular cargoes to the cytoplasm or an organelle.

CPP translocation can be classified into three main entry mechanisms.

1. direct penetration in the membrane.

2. endocytosis-mediated entry.

3. and translocation through the formation of a transitory structure.

Cell-penetrating peptides (CPP) are able to transport different types of cargo molecules across plasma membrane of the liver; thus, they act as molecular delivery vehicles. Cell-penetrating peptides have found numerous applications in medicine as drug delivery agents in the treatment of different diseases including cancer and virus inhibitors, as well as contrast agents for cell labeling. the cooncentration of sally's amino acid was found to be 12.3 picomolars but in the liver it was 4.3, thus it was broken down before absorbtion and then the fractions were transported into the liver aided by CPPs.

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