Why does plasmid recombination require precise "copying and pasting" but microinjection doesn't?

Question

Just learning about biotechnological techniques of gene transfer at the moment. With bacterial plasmid recombination, from a high-school level, we are taught that:

1. The desired gene is cut using a particular restriction enzyme
2. The plasmid from the host is also cut using the same restriction enzyme
3. The desired gene is inserted into the space that was cut out from the plasmid.
4. The plasmid is put back into the bacteria and the gene can now be expresesd.

This makes logical sense.

With microinjection, however, we are taught that the gene is just directly injected into the cell using a needle and that it somehow manages to use it? How does that actually work? How does the extra gene just somehow get put into the existing DNA without cutting out a section like you have to do in plasmid recombination? Furthermore, if you can just insert the DNA into the cell with microinjection without all of the hassle of precise "copying and pasting" done in plasmid recombination, then what is the point of using plasmid recombination?

Answer 1

You can't microinject a bacterium for one thing - far too small, so you need all the components in one place to get the gene expressed and make the plasmid replicable. This will include things like promoters, start sites, Kozak sequences, terminators, resistance genes, ori, etc.

Genes to be microinjected need, at a minimium, sites to make them insert into the host genome by recombination, or need similar components to a plasmid; promoters etc. It's not like this isn't also a precise science in how to get it to work, it's merely that microinjection is one of the techniques used to insert genes into the nucleus of eukaryotic cells.

Answer 2

You can't really determine the exact location of where the insertion will be, and I believe the microinjection you're talking about is using transposons (e.g. P elements).