Which impurities are released along with $DNA$ when cells are broken down for $DNA$ isolation?

$I. ... A...$ is the ability of a cell to take up foreign $DNA$.
$II.$ The cell is treated with a specific concentration of a divalent cation such as $... B...$ to increase the pore size in the cell wall.
$III.$ In $...C...$ method,recombinant $DNA$ is directly injected into the nucleus of an animal cell.
The most appropriate option regarding $A, B$ and $C$ is:

Choose the correct statement:
$P -$ Endonucleases cut the $DNA$ at a specific site inside the $DNA$.
$Q -$ $A$ stirred-tank reactor is usually square in shape.
$R -$ In order to force bacteria to take up the plasmid,the bacterial cells must first be made 'competent' to take up $DNA$ by treating them with a divalent cation like $Ca^{2+}$.

In the process of recombinant $DNA$ technology,proteins and lipids are removed from the medium by which enzymes,respectively?

In the case of polymerase chain reaction $(PCR)$,what are the temperatures required for the following steps?
$A.$ Denaturation
$B.$ Annealing
$C.$ Extension

Select the correct sequence of steps in $PCR$.