Scientific Principle 1-

Genetic modification

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The basic process of Genetic engineering involves removing a piece of genetic coding for a desired trait, which defines for a characteristic, from a donor organism, which is an organism that naturally exhibits the trait, and inserting that gene into the DNA sequence of the host organism, which is an organism that does not naturally exhibit the trait. (ABPI 2015) Subsequently the new genetic information will be replicated during cell division, which is a process that splits one cell into multiple cells, and the trait which it codes for will begin to appear in every new cell. The process of genetic modification has to be carried out during fertilisation, which is stage of sexual reproduction, because otherwise if only one cell in multicellular organism, which is an organism made up of many cells, was modified and changed the immune system, which is responsible for eliminating foreign cells, of the host organism will reject and kill off the newly genetically modified cells as it can not recognise it as one of the pre-existing cells. (Shmaefsky 2006) However since all organism starts off as a single cell and then begins to replicate, the only way for the genetically modified cell to not be rejected as a foreign cell is to make it the first original cell and let it replicate. Thus the female egg cell is modified and fertilised through artificial insemination, which involves manually fertilising the genetically modified egg cell with the sperm cell from a male animal and the fertilised egg is left to replicate and develop. 

 

The first step of genetic engineering involves removing a piece of DNA coding, which is a sequence of genetic information coding for a trait, for the desired trait from a donor organism using an enzyme called "restriction endonucleases". (Arber and Smith 1970) This enzyme is used to slice a DNA strand, which is a strong of DNA coding, at very precise points, thus this enzyme can be used effectively to remove very specific genes. After cutting off a section of DNA, Restriction endonclease leaves a small section of DNA sticking out at both ends known as sticky ends (Davis, 1970s) so that the section of DNA can be easily attached to another piece of DNA.

 

 

 

 

                 

 

 

 

 

 

 

 

 

 

 

 

 

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Image source: hand drawn, image ideas from "abpischools.org.uk"

 

Subsequently a vector molecule (molecule used as a carrier) is used to carry and insert the DNA to the host cell. Commonly used vectors are bacterial plasmid, which is a section of DNA within a bacterium. The advantages of using bacterial plasmids include its independence from the main bacterial genome, which is the main DNA sequence of the bacteria, and ability of rapid replication within the bacterium.

 

The host cell also has a section cut out by restriction endonucleases for the donor DNA sequence to fit into. The sticky ends of the desired gene has a complimentary set (meaning that it corresponds to) the sticky ends in the missing section of the host cell. After the desired gene is attached another enzyme, ligase (Gellert, 1967), is used to join the sticky ends of the two sequences.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Image source: hand drawn, image ideas from "abpischools.org.uk"

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Image Source: hand drawn, image ideas from "abpischools.org.uk"

 

However for the purposes of pharming the piece of DNA coding is usually artificially synthesised, which means artificially and manually created, with pharmaceutical value. The process of artificial synthesis involves using another type of enzymes known as "reverse transcriptase" which builds the desired DNA code from isolated pieces of messenger RNA (signal bases produced during the process of DNA replication).  (ABPI 2015)

 

Ultimately the completed plasmid carrying the desired gene is inserted into the nucleus of the female egg which is subsequently artificially fertilised to form a zygote with the diploid number of chromosomes. The zygote can then undergo mitosis to begin replication of the desired gene within every cell.