Biochemistry USMLE Step 1 questions and answers

Achondroplasia involves what defect? – Cell-signaling defect of fibroblast growth factor (FGF) receptor 3 Marfan's syndrome involves a mutation in what? – Fibrillin gene Xanthine, hypoxanthine and uric acid are all what type of base? – Purine What is the rate limiting step in Purine de novo synthesis? – PRPP step via glutamin PRPP amidotranferase PRPP amidotransferase inhibited by what downstream products in purine synthesis? – IMP, GMP, AMP and puring analogs Allopurinola and 6- mercaptopurine What are the required cofactors for purine de novo synthesis? – THF, glutamine, glycine, aspartate, CO2 Name two crucial enzymes involved in purine salvage pathways – hypoxanthine Phosoribosyltransferaase (HGPRT) anf Adenosine Deaminase. HGPRT converts guanine to ______ and hypoxanthine to _______. – GMP; IMP