Ch. 2— Introduction • 39 
read like a hook. By tlie ld7()'s, l•(>seal'ehers liad 
leai'ned to read the code of certain |)rot(*ins, 
sMithesize tlieir 1).\ \, and insei't the l)\ \ into 
hactei'ia so that the protein couUi he* pioduced. 
(See figure 11.) 
Meanwhile, othei’ scientists were studying 
the genetics ot xii'iises and hactei'ia. The com- 
hination ot these studi(\s with those iinestigat- 
ing the gent'tic code led to the inno\ations ol 
genetic engineei'ing. 
Figure 11.— The Expression of Genetic Information 
in the Cell 
DNA m mRNA ■ » Protein 
(Transcription) (Translation) 
process process 
The "central dogma” of molecular biology: DNA in the 
genes is transcribed into messenger RNA (mRNA) which is 
then translated by reactions in the cell into protein. Each 
gene contains the information for a specific protein. 
SOURCE: Otlice of Technology Assessment. 
Developing genetic technologies 
In the each 196()'s. scientists disco\ered e.\- 
actly how geties mo\e Irom one hacterium to 
atiother. One such mechanism irses hacttM'io- 
phages— viruses that inlect bacteria— as int(M'- 
tuediaries. F’hages act like In podertnic needles, 
injecting their 1),\.\ into hactenial hosts, where 
it resides hel'ore being passed along from one 
generation to the next as part of the bacterium's 
own D.\,\. Sotiietimes, however, the injected 
ON \ enters an activ e phase and produces a crop 
of new V irus pai'ticles that can then hurst out of 
their host. Often during this [jrocess, the viral 
0.\.\ inadv ertently takes a piece of the bacterial 
l)\.\ along w ith it. I hus, vv Ikmi the nrnv virus 
particUxs now infect other bacteria, they bring 
along srneral genes from their pi'evious host. 
This viral transduction— the transfer of genes 
by an intei'mediate viral vector or vehicle— 
could he used to confer new genetic traits on 
recipient bacteria. (See figure 12.) 
hactei'ia also transfer genes directly in a proc- 
ess called conjugation, in which one hacterium 
attaches small projections to the surface of a 
nearby hacterium. DN',\ from the donor hacte- 
rium is then |)assed to the recipient through the 
Figure 12.— Transduction: The Transfer of Genetic Material in Bacteria by Means of Viruses 
Bacterium 
Bacterial 
In step 1 of viral transduction, the infecting virus injects its DNA into the cell. In step 2 when the new viral particles are 
formed, some of the bacterial chromosomal fragments, such as gene A, may be accidently incorporated into these progeny 
viruses instead of the viral DNA. In step 3 when these particles infect a new cell, the genetic elements incorporated from the 
first bacterium can recombine with homologous segments in the second, thus exchanging gene A for gene a. 
SOURCE: Office of Technology Assessment. 
