Question

Laboratory techniques for randomly linking together amino acids typically generate an insoluble polypeptide, yet a naturally occuring polypeptide of the same length is usually soluble. The polypeptide synthesized in a living cell has a sequence that has been optimized by natural selection to fold properly. Explain

Answer 1

The polypeptide chain synthesised by living cells has amino acid composition in a way which allows its proper folding and hence makes it soluble. Hydrophobic amino acids are hidden inside and hydrophilic polar amino acids are exposed on the surface. The polar ones interact with each other to make hydrogen bond and other bonds which makes the polypeptide structure more compact, stable and soluble.

When the polypeptide is synthesised in lab with random amino acid composition, the sequences do not fit properly with each other. Hydrophobic side chains are exposed on surface and get aggregated due to which the polypeptide becomes insoluble and precipitates in the solution.

Answer 2

Translation may be defined as the process of formation of the protein product from the RNA molecule. The proteins gets fully folded and acquire proper 3D shape to become functionally active.

The polypeptides optimized by natural selection folds properly because the polypeptides has both the hydrophobic residues inside the protein and polar residues on the surface of protein. The random sequence present in the synthetic peptide will not direct the correct coherent folding process. The hydrophobic side chains that are present on the different molecules aggregate that causes the precipitation of polypeptide in the solution.