Mechanisms of Genetic Exchange and Recombinant DNA Techniques
1. Define:
Transformation - Transformation is a naturally occurring genetic exchange mechanism allowing DNA to be transferred from dead donor cells to live recipients. It can also be viewed as a mechanism allowing bacteria to pick up naked DNA from their environment. This process was first observed to occur in Steptococcus pneumoniae that had been introduced into mice. DNA transferred through transformation may be incorporated into the chromosome of the host, or remain separate (as a plasmid).
Episome - An episome is a segment of extrachromosomal DNA that can become incorporated into the chromosome. The DNA involved may be either plasmid DNA or viral DNA. Note - Although some references define episomes as being plasmids, others consider bacteriophage lambda DNA to be an episome, and it is viral DNA.
Sexduction - Sexduction is a specific type of conjugation that involves the "mating" of an F' (F-prime) with an F- (F-minus) cell, and which results in the formation of a cell that is male, F' (F-prime), recombinant and partially diploid.
Transduction - Transduction is a genetic exchange mechanism involving the transfer of DNA from a donor cell to a recipient cell via a virus. Transduction may be categorized as either specialized (specific) or generalized.
Restriction endonuclease - The restriction endonuclease enzymes (restriction enzymes) are enzymes that cut double-stranded DNA (they break phosphodiester bonds). The most useful of these cut the DNA in a site specific manner, i.e., they bind the DNA at specific nucleotide sequences known as recognition sequences, and then cut within or near these sequences (always in the same place). These enzymes probably evolved as a defense against viruses, because they do tend to recognize foreign DNA and "chop" it up.
2. recombinant DNA/genetic exchange
3. recombinate DNA
4. restriction endonucleases (restriction enzymes)
5. homologous
6. The genetic exchange processes that occur in bacteria are all similar in that: 1) the cells involved do not fuse to form a zygote, 2) usually only a small amount of DNA is exchanged, 3) the exchange is one way, i.e., from a donor to a recipient, but not back again, 4) the process is more likely to be successful if the organisms involved are closely related (within the same species), and 5) the DNA that is transferred usually replaces homologous DNA already present.
7. fuse to form a zygote/ bacteria contain restriction enzymes that will recognize and "chop up" foreign DNA. Note - Some bacteria can only bind DNA with a species-specific nucleotide sequence, so can only take in DNA carrying that sequence.
8. transformation (DNA mediated transformation)/ Steptococcus
9. naked DNA from their environment/ competent
10. conjugation/sexduction
11. sex pili/ F factor or F plasmid
12. episome
13. high frequency recombinant (Hfr)
14. sexduction/ recombinant/ partial diploid
15. generalized transduction
16. specialized transduction
17. replicon or cloning vector
18. cosmid
19. I,H,G,B,C,J,D,E,A,F Note - The term transduction is missing from the first and last terms in this set. The first term should be specialized transduction, and the last generalized transduction.
Copyright 2002 Sierra College Biological Sciences Department
Last updated: 01/18/02.
