CLINICAL CASES
47
HIV:
Human immunodeficiency virus; a retrovirus that causes acquired
immunodeficiency syndrome (AIDS).
Retrovirus:
A virus in which the genetic material located in the virus is
RNA. The genetic information in the retrovirus must be converted to
DNA in the host by the process of reverse transcription.
Reverse transcription:
The synthesis of DNA from an RNA template.
Transcription:
The process by which the information contained in the
nuclear DNA is converted to cytosolic mRNA. This is accomplished by
RNA polymerases that synthesize an mRNA that has a complementary
sequence to the DNA strand that was used as the template.
Translation:
The synthesis of proteins from mRNA. This is a process that
takes place on ribosomes and requires the participation of aminoacyl-
charged tRNAs, mRNA, and various initiation and elongation factors.
Exons:
Sequence of nucleotides that appear in mature RNA.
Introns:
Sequences of nucleotides that do not appear in mature RNA but
are excised and do not appear in messenger RNA.
Spliceosome:
A complex of small nuclear ribonucleoprotein particles
(snRNPs) that catalyze the splicing, or removal of introns, of mRNA
precursors.
D ISC U SSIO N
DNA is the biological blueprint material,
which authentically carries all the
necessary cellular information and passes it from generation to generation.
Thus, it is essential for the cells to preserve the integrity of the DNA and keep
it as error free as possible. One is amazed with the versatile DNA molecule,
which dictates both the unique and the similar features of the offspring from
its parents. What are the processes that take place in a cell to duplicate and
interpret this genetic code into functional signals? DNA is duplicated in a
semiconservative fashion
in a process called
DNA replication.
DNA interpretation
follows the central dogma (Figure 5-1): first, the DNA
is
decoded to form
messenger RNA
(mRNA)
in the nucleus by a process called
transcription. Transcription
is a complex process involving an
enzyme RNA
TRANSCRIPTION
^
TRANSLATION
DNA
«
RNA ---------------------------------------------► Protein
Reverse TRANSCRIPTION
mRNA
Protein
5;______ AUG__
N
UAA-poly(A)
C
Figure 5-1.
The central dogma.
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