CBSE Biochem (100% correct)

Lesch-Nyhan Syndrome: what causes it and what are manifestations? correct answers 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? correct answers 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? correct answers 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? correct answers Because in some tissues, de novo purine synthesis is not possible. How are nucleotide monophosphates created? correct answers 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? correct answers 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? correct answers Missense mutation--valine replaces glutamic acid. Tay-Sachs and Duchenne Muscular Dystrophy are caused by which mutation type? correct answers Frameshift Xeroderma Pigmentosum: is caused by a defect in what specifically? correct answers 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. How is spontaneous / toxic deamination repaired? correct answers Base excision repair--involves AP endonucleases throughout the cell cycle What is defective in Lynch Syndrome? What is another term for Lynch Syndrome? correct answers Lynch syndrome= hereditary nonpolyposis colorectal cancer. Mismatch repair is defective. This usually occurs in G2 of cell cycle.