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:

• 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

Circular chromosome

Ribosomes

Plasmid

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. The gene to be transferred is identified on the chromosome.2. The gene is cut from the chromosome using an enzyme3. The gene to be transferred is put into a bacterial plasmid (or into a virus that will take it into a bacterial cell)4. 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