Biology Unit 2 Revision notes

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  • Created on: 20-04-11 16:43

Genetic Engineering

1. Genetic engineering is the removal of genes from one organism and insertion into another.

2. The genome is the entire DNA sequence of an organism, i.e. all of the genes and the entire noncoding DNA in between.

3. A transgenic organism is one that has had its DNA altered by the insertion of genes from another 


4. Recombinant DNA is DNA that has been mixed with the DNA of another species. Usually the 

entire genome will be intact – only one or two specific genes are added.

5. Restriction endonuclease enzymes will cut DNA at a specific base sequence. They will cut in a 

staggered manner to make ‘sticky ends’ on the DNA cut. Sticky ends can be joined together using 

ligase enzymes.

6. DNA can be isolated from cells for use in genetic engineering:

a. For plant cells, the cellulose cell walls must be physically broken up by grinding in sand.

b. This is placed in a buffer solution, along with SDS detergent to emulsify lipids and break 

down membranes within the cells. It is incubated at 65°C to disrupt the proteins.

c. This mixture is then centrifuged to remove the cell debris and leave the DNA in the 


d. Adding ice-cold ethanol will cause the DNA to form a precipitate, which can be removed.

7. In order to locate a specific gene:

a. The polypeptide for which the gene codes is analysed and converted into an mRNA 


b. The mRNA is converted into DNA using the enzyme reverse transcriptase, in the 

presence of radioactively labelled cytosine.

c. This is then used as a radioactive gene probe, so when it is added to the DNA it will bind 

to the gene, pinpointing its location.

8. Plasmids are small circles of DNA found in bacteria that can be used as a vector – i.e. as the carrier 

of another gene.

9. To incorporate a gene into a bacterium:

a. Use a restriction endonuclease enzyme to cut out the gene that is needed.

b. Isolate a bacterial plasmid, and use the same restriction endonuclease to cut it, so as to 

produce complementary sticky ends.

c. Splice the DNA into the plasmid with ligase enzymes

d. Place the vector DNA (the plasmid) into a bacterium…


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