Lesch-Nyhan Syndrome: what causes it and what are manifestations? - ✔✔HGPRT deficiency in
purine salvage pathway (this enzyme normally converts hypoxanthine to IMP and guanine to
GMP). This deficiency leads to excessiv
...
Lesch-Nyhan Syndrome: what causes it and what are manifestations? - ✔✔HGPRT deficiency in
purine salvage pathway (this enzyme normally converts hypoxanthine to IMP and guanine to
GMP). This deficiency leads to excessive Uric acid production and de novo purine synthesis. It
is X linked recessive. Symptoms: hyperuricemia, gout, aggression / self mutilation, mental
retardation, dystonia.
Treatment for Lesch-Nyhan? - ✔✔Allopurinol / febuxostat second line. Both of these drugs
inhibit xanthine oxidase, which converts hypoxanthine to xanthine and xanthine to uric acid.
Adenosine Deaminase Deficiency: what is it, what effects does it have? - ✔✔ADA is required
for degradation of adenosine and deoxyadenosine--dATP builds up and is toxic to lymphocytes,
which is why this disease is a major cause of SCID--severe combined immunodeficiency
(Autosomal recessive).
Why is purine salvage important? - ✔✔Because in some tissues, de novo purine synthesis is not
possible.
How are nucleotide monophosphates created? - ✔✔Activated ribose-5-phosphate (PRPP) is
added to bases by phosphoribosyltransferases (HGPRT and APRT are the two types of this
enzyme).
tRNA Wobble: what is it and it causes which type of mutation? - ✔✔An unusual pairing of bases
in the third position of the codon--causes silent mutation.
Sickle Cell Anemia is caused by which type of mutation? - ✔✔Missense mutation--valine
replaces glutamic acid.
Tay-Sachs and Duchenne Muscular Dystrophy are caused by which mutation type? -
✔✔FrameshiftXeroderma Pigmentosum: is caused by a defect in what specifically? - ✔✔Nucleotide excision
repair--pyrimidine dimers are not repaired (caused by UV exposure). In nucleotide excision
repair, bulky helix-disturbing lesions are repaired by endonucleases. This occurs during G1 of
cell cycle.
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