AQA A Level Biology复习笔记8.4.1 Recombinant DNA Technology

Recombinant DNA

• The genetic code is universal, meaning that almost every organism uses the same four nitrogenous bases – A, T, C & G. There are a few exceptions
• The genetic code is the basis for storing instructions that, alongside environmental influences, dictate the behaviour of cells and as a result, the behaviour of the whole organism
• The universal nature of the genetic code means that the same codons code for the same amino acids in all living things (meaning that genetic information is transferable between species)
• Thus scientists have been able to artificially change an organism's DNA by combining lengths of nucleotides from different sources (typically the nucleotides are from different species)
• The altered DNA, with the introduced nucleotides, is called recombinant DNA (rDNA)
• If an organism contains nucleotide sequences from a different species it is called a transgenic organism
• Any organism that has introduced genetic material is a genetically modified organism (GMO)
• The mechanisms of transcription and translation are also universal which means that the transferred DNA can be translated within cells of the genetically modified organism

Illustration of a maize plant that has recombinant DNA (DNA from Bacillus thuringiensis).

Recombinant DNA technology

• This form of genetic engineering involves the transfer of fragments of DNA from one organism/species into another organism/species
• The resulting genetically engineered organism will then contain recombinant DNA and will be a genetically modified organism (GMO)
• In order for an organism to be genetically engineered the following steps must be taken:
  • Identification of the DNA fragment or gene
  • Isolation of the desired DNA fragment
  • Multiplication of the DNA fragment (using polymerase chain reaction - PCR)
  • Transfer into the organism using a vector (e.g. plasmids, viruses, liposomes)
  • Identification of the cells with the new DNA fragment (by using a marker), which is then cloned

   

• Genetic engineers need the following to modify an organism:
  • Enzymes (restriction endonucleases, ligase and reverse transcriptase)
  • Vectors - used to deliver DNA fragments into a cell (eg. plasmids, viruses and liposomes)
  • Markers - genes that code for identifiable substances that can be tracked (eg. GFP - green fluorescent protein which fluoresces under UV light or GUS - β-glucuronidase enzyme which transforms colourless or non-fluorescent substrates into products that are coloured or fluorescent)

   

• Genetic engineering is being used in the new field of science called synthetic biology
  • This is an area of research that studies the design and construction of different biological pathways, organisms and devices, as well as the redesigning of existing natural biological systems

   

An overview of the steps taken to genetically engineer an organism (in this case bacteria are being genetically engineered to produce human insulin)