DNA
EXAM 23rd..subjek DR.CHan Kok GAn..
ermm..fiNal ExAm ni 60%...
wHAt IS tr DNA aLL about?
is aLL aBout GEne..
GENE cloNing...
gene yg kita berminat, boleh diambik..dan di klon.. dan di masukkan pada organisma baru...
lebih kurg camtula..ermm,
answer.com
1. Methods for breaking and rejoining DNA. The precise breaking and rejoining of DNA has been made possible by the discovery of restriction endonucleases, enzymes that have the ability to recognize specific DNA sequences and to cleave the double helix precisely at these sites. Also important are the ability to join fragments of DNA together with the enzyme DNA ligase, and the techniques to determine the nucleotide sequence of genes and thereby confirm the identity and location of structural and regulatory sequences.
2. Carriers for genetic sequences. Bacterial plasmids, that is, circular double-stranded DNA molecules that replicate extrachromosomally, have been modified so that they can serve as efficient carriers for segments of DNA, complete genes, regions of genes, or sequences contained within several different genes. Bacteriophage and animal viruses, retroviruses, and bovine papilloma virus have also been successfully utilized as DNA carriers. These carriers are referred to as cloning vectors. Host cells in which vectors containing cloned genes can replicate range from bacteria to numerous other cells, including normal, transformed, and malignant human cells.
3. Introduction of recombinant DNA molecules. Genetic sequences in the form of isolated DNA fragments, or chromosomes, or of DNA molecules cloned in plasmid vectors can be introduced into host cells by a procedure referred to as transfection or DNA-mediated gene transfer—a technique that renders the cell membrane permeable by a brief treatment with calcium phosphate, thereby facilitating DNA uptake. Genes cloned in viruses can also be introduced by infection of host cells.
4. Selection of cells containing cloned sequences. Bacterial cells containing plasmids with cloned genes can be detected by selective resistance or sensitivity to antibiotics. In addition, the presence of introduced genes in bacterial, plant, or animal cells can be assayed by a procedure known as nucleic acid hybridization.
5. Amplification. Amplification of genetic sequences cloned in bacterial plasmids is efficiently achieved by treatment of host cells with antibiotics which suppress replication of the bacterial chromosome, yet do not interfere with replication of the plasmid with its cloned gene. Sequences cloned in bacterial or animal viruses are often amplified by virtue of the ability of the virus to replicate preferentially.
6. Expression. Expression of cloned human genes can be mediated by regulatory sequences derived from the natural gene, from exogenous genes, or by host cell sequences.jom..say tq to new era of technology!
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