National 5 Biology Course Notes
Unit 1 : Cell Biology
Part 6 :
Genetic Engineering
Structure of bacteria
Bacterial cells are different from plant and animals cells because:
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Although they have cell walls like plant cells, bacterial cell walls are chemically different
They have a cell membrane and ribosomes but don’t have any other organelles found in plant and animal cells
They don’t have a nucleus but just have a single circular chromosome.
They have circles of DNA separate from the chromosome called plasmids
Bacterial cell diagram
Cell wall
Cell membrane
Plasmid
Ribosomes
Circular chromosome
Transfer of genes between cells
Genes can be transferred between cells naturally or by genetic engineering
Transfer of genes naturally
This can be brought about by:
Viruses
Transfer of plasmids (and the genes they contain) from one bacterial cell to another
Genetic engineering
Genetic engineering involves taking a gene from one organism, e.g. a human gene, and transferring it to a
different organism (e.g. a bacterium).
The organism receiving the transferred gene will now produce the protein coded for by the gene.
Human genes for the hormones insulin and human growth hormone have been put into E. coli bacteria
allowing the bacteria to make these hormones to treat diabetes and pituitary dwarfism.
Stages in genetic engineering
1.
2.
3.
4.
The gene to be transferred is identified on the chromosome.
The gene is cut from the chromosome using an enzyme
The gene to be transferred is put into a bacterial plasmid (or into a virus that will take it into a bacterial cell)
The plasmid containing the new gene is placed into a bacterial cell. (the cell is now a genetically modified (GM)
organism).
5. The bacterial cell containing the transferred gene reproduces and produces the protein the gene codes for.
Gene to be transferred is
identified and cut from the
chromosome using an
enzyme
Gene is joined to
the plasmid using
an enzyme
Plasmid containing the
transferred gene is placed
into a bacterial cell
“Host” bacterial cell and the
plasmid it contains reproduce
to make more copies of the
transferred gene
Protein made by the gene, e.g. insulin, is
extracted and purified