chapter 21 part 2 COPY Flashcards
different techniques in Synthetic biology:
**genetic engineering **
this may involve a single change in a biological pathway or relatively major genetic modification of an entire organism
** use of biological systems or parts of biological systems in industrial contexts**
for example, the use of fixed or immobilised enzymes and the production of drugs from microorganisms
the synthesis of new genes to replace faulty genes
for example, in developing treatments for cystic fibrosis (CF)
scientists have attempted to synthesise functional genes in the laboratory and use them to replace the faulty genes in the cells of people affected by CF
** the synthesis of an entire new organism**
In 2010, scientists announced that they had created an artificial genome for a bacterium and successfully replaced the original genome with this new, functioning genome.
Synthetic life - new bases? part 1
Scientists have developed some new nucleotide bases (not adenine, thymine, cytosine, or guanine) which, in a test tube, can be incorporated into a strand of DNA by special enzymes.
The bases fit together well - they are not held by hydrogen bonds like the natural bases.
In 2014, scientists introduced a small section of DNA made with these synthetic bases into bacteria.
Synthetic life - new bases? part 2
They found that this unique DNA, including the synthetic nucleotide bases, was replicated time after time as long as they supplied the bacteria with the synthetic bases.
If these bases can be incorporated into the main DNA of an organism, and then transcribed into RNA, synthetic biologists will have synthetically expanded the genetic code for the very first time.
Infection outbreak - DNA sequencing and clinical intervention:
part 1
In 2012, there was an outbreak of MRSA (methicillin-resistant Staphylococcus aureus) in the Special Care Baby Unit (SCBU) at a UK hospital.
The hospital infection control team identified 12 patients carrying MRSA.
Researchers at the Wellcome Trust Sanger Institute used DNA sequencing to show that all the bacteria were closely related and this was a hospital-based outbreak.
The sequencing also showed that a number of people living in the community who developed MRSA at the same time all had the same strain as the hospital outbreak.
In every case it was found they had a recent link to the hospital.
Two months later, another baby developed MRSA in the same SCBU.
Immediate DNA sequencing showed that it was the same strain as the previous outbreak.
This suggested that someone working in the hospital was unknowingly carrying MRSA.
Infection outbreak - DNA sequencing and clinical intervention: part 2
Sequencing the genome of pathogens so that effective treatment can be introduced as fast as possible and outbreaks halted is a big step forward
Over 150 healthcare workers were screened - and one staff member was found to be carrying MRSA.
DNA sequencing confirmed that it was the strain linked to the outbreak. The healthcare worker went through a process to eradicate the MRSA - and the risk of any further infections was removed.
The use of DNA sequencing was critical in identifying that the infections were connected and that a member of staff was a carrier.
Without it, this would have been seen as a new outbreak, and many more people could have been infected.
This was the first time DNA sequencing has led to an immediate and successful clinical intervention - but it will certainly not be the last.
definition of genetic engineering.
The manipulation of the genome via Advances in these technologies (DNA sequencing and proteomics) and molecular biotechnology techniques means it is now possible to manipulate an organism’s genome to achieve a desired outcome.
The basic principles of genetic engineering:
isolating a gene for a desirable characteristic in one organism and placing it into another organism, using a suitable vector.
The two organisms between which the genes are transferred may be the same, similar, or very different species.
An organism that carries a gene from another organism is termed ‘transgenic’ and is often called a genetically modified organism (GMO).
Isolating the desired gene: part 1
The first stage of successful genetic modification is to isolate the desirable gene.
The most common technique uses enzymes called restriction endonucleases to cut the required gene from the DNA of an organism.
DNA profiling, each type of endonuclease is restricted to breaking the DNA strands at specific base sequences within the molecule.
Isolating the desired gene: part 2
Some make a clean, blunt-ended cut in the DNA, However, many restriction endonucleases cut the two DNA strands unevenly, leaving one of the strands of the DNA fragment a few bases longer than the other strand (Figure 2).
These regions with unpaired, exposed bases are called sticky ends.
The sticky ends make it much easier to insert the desired gene into the DNA of a different organism.
Another technique of genetic engineering
Another technique involves isolating the mRNA for the desired gene and using the enzyme reverse transcriptase to produce a single strand of complementary DNA.
The advantage of this technique is that it makes it easier to identify the desired gene, as a particular cell will make some very specific types of mRNA.
For example, B cells of the pancreas make insulin, so produce lots of insulin mRNA molecules.
diagram of the production of human insulin by genetically engineered bacteria
diagram of restriction endonucleases isolating a gene
The formation of recombinant DNA
The DNA isolated by restriction endonucleases must be inserted into a vector that can carry it into the host cell.
How To insert a DNA fragment into a plasmid: part 1
first it must be cut open.
The same restriction endonuclease as used to isolate the DNA fragment is used to cut the plasmid.
This results in the plasmid having complementary sticky ends to the sticky ends of the DNA fragment.
Once the complementary bases of the two sticky ends are lined up, the enzyme DNA ligase forms phosphodiester bonds between the sugar and the phosphate groups on the two strands of DNA, joining them together
How To insert a DNA fragment into a plasmid: part 2
The plasmids used as vectors are usually given a second marker gene, which is used to show that the plasmid contains the recombinant gene.
This marker gene is itself often placed in the plasmid by genetic engineering methods.
The plasmid is then cut by a restriction enzyme within this marker gene to insert the desired gene.
If the DNA fragment is inserted successfully, the marker gene will not function.
