Biology Reference
In-Depth Information
Figure 1.1
The Central Dogma assumes that biological information transfers from DNA to RNA
to proteins. Recent discoveries of viruses that transcribe information from RNA to DNA required
modification in the Dogma. Three processes are involved in the Central Dogma: DNA replication,
transcription of the genetic information into RNA, and translation of the mRNA into a polypeptide
(protein).
subsequently is transferred to RNA (mRNA), and finally it is translated into spe-
cific proteins based on the code in the DNA. Initially, the Central Dogma stated
that the flow of information is unidirectional, with proteins unable to direct the
synthesis of RNA, and RNA unable to direct the synthesis of DNA (
Figure 1.1
).
The Central Dogma had to be amended in 1970 when certain viruses were
found to transfer information from RNA to DNA. Subsequently, mutated pro-
teins found in the membrane of brain cells of vertebrates were shown to be
inherited. Although such aberrant proteins initially were thought to be caused
by slow viruses or viroids, Stanley Prusiner discovered that the mutated pro-
teins (called
prions
) could cause a group of fatal neurodegenerative diseases.
The term
prion
refers to
pr
oteinaceous
in
fectious particles (
Prusiner and Scott
1997
) that cause diseases such as bovine spongiform encephalopathy (“mad cow
disease”) in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease or kuru in
humans. These proteinaceous infective particles do
not
contain DNA, but they
are able to transmit the disease to individuals who eat the altered proteins
(
Prusiner and Scott 1997
). The altered protein acts as a template upon which the
normal protein is refolded into a deformed molecule through a process facili-
tated by another protein (
Prusiner and Scott 1997, Tuite 2000
). Such abnormal
proteins are transmitted to daughter cells, thereby propagating the mutant
phenotype in the absence of any mutated nucleic acid.
The Central Dogma remains an important tenet of modern biology, although
our knowledge of the roles of RNAs continues to expand and some have ques-
tioned its relevance (
Mattick 2009, Shapiro 2009
). In insects, genes (DNA) are
found in complex structures called chromosomes that consist of proteins, RNAs,
and DNA. This chapter reviews the structure of DNA and RNA, the basis of the
