CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 9: E R Y T H R O M Y C IN
A N D LY M E D ISE A SE
A 40-year-old male who presents with migrating arthralgias and neu-
rologic changes which were preceded by a centrally clearing circular rash, myal-
gias, and headache after a hunting trip where he was exposed to fleas and ticks.
Diagnosis: Lyme disease
Biochemical site of action of erythromycin: Inhibits bacterial protein
biosynthesis at the translocation step of translation
C L IN IC A L C O R R E L A T IO N
Lyme disease is a multisystem disease caused by the spirochete (spiral-shaped
nearly always transmitted by tick bite. Lyme
disease is much more common in the New England area, usually during the
late spring and early summer months. The deer tick is the main vector of trans-
mission. The first stage is an acute infection with a red papule developing at
the site of the bite, sometimes with lymphadenopathy and fever. The second
stage includes disseminated infection and can lead to involvement of the heart,
brain, joints, and skin. The typical target-shaped skin lesions may be seen. The
third stage is a chronic infection and may last for years. Antibiotics are the
treatment of choice, usually tetracyclines or penicillins.
A PPR O A C H TO PR O T E IN B IO SY N T H E SIS
Understand protein biosynthesis (initiation, elongation, translocation,
Know key differences between prokaryotic and eukaryotic protein
Know the role of ribosomal ribonucleic acid (rRNA).
Know the mechanism of action of different antibiotics with protein
A-site: The acceptor site on the ribosome into which an aminoacyl-charged
transfer RNA (tRNA) is brought that has an anticodon that is comple-
mentary to the messenger RNA (mRNA) codon. The ribosome will then
catalyze the formation of a peptide bond with the aminoacyl group on
this tRNA and the growing peptide chain.