Genetic engineering tools, recombinant proteins and GM organisms

Last time

Before we start: last time, in Gene therapy, gene editing, microarrays and bioinformatics, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Cut, paste, copy

Genetic engineers work like molecular editors. They cut a gene out of one organism, paste it into a carrier, and put the carrier into another. The bacteria, crop plants or animals that result then make a new protein. Every tool in the kit is an enzyme or a piece of D N A you have already met, now used on purpose.

What genetic engineering is

Genetic engineering is the transfer of a gene from one organism, the donor, into another organism, the recipient, so that the recipient makes the protein coded by that gene. The product is a transgenic or recombinant organism. It works because the genetic code is universal, so a human gene can be read by a bacterium. The steps are: obtain the gene, cut it and the vector, join them, put the new D N A into host cells, and identify the cells that took it up.

Getting the gene

The gene can be cut out of the donor D N A by restriction enzymes. But in humans, the gene is hard to find among three billion base pairs. Alternatively, the messenger R N A for the protein is extracted from cells that make a lot of it. Reverse transcriptase makes complementary D N A, c D N A, from the mR N A. This has no introns. Or the gene is made in a gene machine if the protein sequence is known, building the D N A nucleotide by nucleotide.

Cutting and joining

A restriction enzyme cuts D N A at a specific base sequence, the recognition site. Eco R I recognises G A A T T C, which reads the same on both strands. It cuts in a staggered way, leaving short single stranded ends, called sticky ends. Sticky ends of the gene and vector are complementary, and base pair. D N A ligase joins the sugar phosphate backbones, forming phosphodiester bonds, and makes recombinant D N A.

A past-paper example

October November 2024, Paper 41, question 8 part a. When the gene cannot be extracted from the donor, it is synthesised. Outline the two methods for synthesising a gene. One method is to use reverse transcriptase to make c D N A from the mRNA. The other is to use a gene machine, building the D N A from the known amino acid or base sequence. Both give a gene without introns.