CLINICAL CASES
53
[5.3]
E. The HIV proteins synthesized by the host cell are produced as a
long polyprotein that must be cleaved to the active HIV enzymes and
structural proteins. HIV protease inhibitors bind to and inhibit the
aspartic protease that hydrolyzes the polyprotein, thus preventing the
assembly of infective viral particles.
[5.4]
A. The initiator codon is AUG and codes for Met; UCU = Ser;
CGG = Arg; GUU = Val; CUG = Leu; UAA = stop codon. The mRNA
is read in the 5' ^ 3' direction.
B IO C H E M IS T R Y PE A R L S
DNA is decoded to form messenger RNA (mRNA) in the nucleus by
a process called transcription. RNA synthesis is always unidirec-
tional from 5' (phosphate) to 3' (hydroxyl), and begins at the 3'
end of the DNA chain toward the 5' end.
The mRNA is processed in the cytoplasm (translation) involving the
ribosomes. Each triplet nucleotide codon codes for a specific
amino acid (the three-letter genetic code).
Messenger RNA is translated into protein with the help of tRNA,
which brings an amino acid along with it (aminoacyl tRNA) and
ribosomes.
Some viruses such as HIV have RNA genomes, and they usually are
reverse transcribed into a double-stranded DNA molecule by uti-
lizing the reverse-transcriptase enzyme.
REFERENCES
Levy JA. HIV and the Pathogenesis of AIDS, 2nd ed. Washington DC: ASM Press,
1998.
Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology, 4th ed. New York:
Freeman, 2000.
Raffanti S, Haas DW. Anti-bacterial agents. In: Goodman AG, Gilman LS, eds. The
Pharmacological Basis of Therapeutics, 10th ed. New York: McGraw-Hill, 2001.
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