Notes:
1) Genetic recombination refers to the rearrangement of DNA from separate group of genes.
2) Genetic transfer refers to the exchange between2 DNA to form new combinations of genes in a chromosome.
3) Donor cell is the cell that gives a portion of its total DNA and recipient cell that recieved a portion of DNA from donor cell.
4) When the donor's DNA have been incorporated into the recipient's DNA, the resultant cell is called a recombinant.
5) Transformation occurred when gene transfer from one bacterium to another as 'naked' DNA in solution.
6) Griffith's experiment proved the occurring transformation and the hereditary materials as the transforming agent.
A short explanation about Griffth's experiment:
Streptococcus pneumoniae is used in this experiment. Strain S is virulent and has a capsule on it. Strain R is avirulent and has no capsule on it. When live strain R and dead strain S are injected into a mice individually, the mice survived. When live strain S injected into a mice, the mice died. When live strain R + dead strain S injected into a mice, the mice died.
Conclusion: DNA from virulent cell can enter avirulent cell , changing the avirulent strain genetically to make it become virulent.
7) Avery's experiment proved that DNA carried genetic information for transformation but not protein.
A short explanation about Avery's experiment:
Extraction of polysaccharides, lipids, DNA, RNA and protein from strain S pneumococci by chromotography and each of these extraction added individually into strain R. Strain R turns into virulent only when extracted DNA from strain S is added into strain R.
Conclusion: DNA carries genetic information for transformation but not other materials
8) Competence is the alterations in the cell wall that make it permeable to large DNA molecules.
9) Recipient cells have to be competent to take up the donor DNA. Some bacteria are naturlly competent but some undergo treatment to make it competent.
10) Transduction is the transfer of DNA from donor to recipient via a bacteriophage.
11) There are two types of transduction:
- Generalized transduction
- bacteriophase attack the bacterial host and hydrolysed the bacterial DNA to mix with viral DNA. New protein coat is build up and some bacterial DNA are packaged in a phase caspid. Then the donor lysed release the phase containing bacterial DNA. The phase which contained bacterial DNA is now infect other recipient bacteria cell. Recombination occur, producing a recombinant cell with a genotype different from both the donor and recipient cells.
- The viral DNA is not being transferred in generalized transduction because viral DNA is not integrated into the bacterial genome.
- Specialized Transduction
- bacteriophase attack the bacterial host and viral DNA inserted into the bacterial host to integrate into the bacterial genome. The viral genome integrated into the bacterial genome is called prophage. Upon induction, the prophage detaches from the bacterial chromosome. A portion of bacterial DNA remained attach to the detached phase DNA. Therefore, this excised phage infects another bacterium and transfers the bacterium genes from the donor bacterium.
-Only the bacterial gene that close to the site of prophage are transferred.
12) Plasmids are self-replicating covalently closed circular DNA molecules that are usually not essential for survival. There are three types of plasmid:
- Dissimilation plasmid - code for enzymes for catabolism of certain unusual sugars
- Conjugative plasmid - carries genes for sex pili and transfer of plasmid'
- R factors - carry genes that confer upon their host cell resistance to antibiotics, heavy metals and cellular toxins.
14) Gram-negative bacterial cell used pili for contact while gram-positive bacterial cell used sticky surface molecule for contact.
15) There are two types of conjugation transfer:
- Plasmid transfer
- Sex pillus is formed between F+ and F- . F factor replicated and transfer to a F-.
- The F- is converted into F+ .
- Chromosome transfer
- The insertion of F factor into chromosome results Hfr cell.
- Hfr cell can transfer chromosomal DNA into the F- but F- convert into recombinant F- cell but not F+ cell because only part of the chromosome being transferred.
Activities: No other activity carried out except for teaching...^^
My own explorace:
1) Naked DNA is histone-free DNA that is passed from cell to cell during a gene transfer process called transformation.
2) There are two ways to create competent cells: heat shock and electroporation. Chemically competent cells are created using a series of cold salt washes to disrupt the cell membranes, preparing the cells to accept plasmid DNA. For electrocompetent cells, the cells are chilled and washed with cold deionized water and 10% glycerol.
Heat shock : The plasmid DNA is incubated with host cells to make the plasmid to close contact with the host cells. The plasmid-cell mixture is heated to 45 degree celcius to 50 degree celcius to allow the plasmid DNA enter the bacterial through disrupted membrane. The heated mixture is then placed back in ice to retain the plasmid in the bacteria.
Electroporation: The plasmid-cell misture is exposed to electric current to make pores on the membrane, allowing the entry of plasmid to the host cell.
3) Prophase is the viral genome that integrated into the bacterial genome.
4) Hfr means high frequency recombinant.
Reflection:
Genetic transfer is really a great invention of human. Organisms can change their genotype through genetic transfer. The steps are complicated and genetic transfer may need a long time to make it completely success. However, genetic transfer are not popular in Malaysia because we lacks those technology knowledge and equipment to carry out transfer.
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