Give reasons why:
(a) DNA cannot pass into a host cell through the cell membrane.
(b) Proteases are added during isolation of DNA for genetic engineering.
(c) Single cloning site is preferred in a vector.
Answer (a) DNA is a hydrophilic molecule, so it cannot pass into a host cell through cell membrane. The cell membrane consists of lipid bilayers that are generally impermeable to hydrophilic molecules.
(b) DNA is interwined with proteins like histones and RNA. To obtain purified DNA, proteases are added during isolation of DNA which convert proteins into amino acids. The purified DNA finally precipitates out after the addition of chilled ethanol.
(c) In order to link the alien DNA, the vector needs to have very few, preferably single, recognition sites for the commonly used restriction enzymes. Presence of more than one recognition sites within the vector will generate several fragments, which will complicate the gene cloning process.
