Biochemistry USMLE Step 1 UPDATED
ACTUAL Exam Questions and CORRECT
Answers
Achondroplasia involves what defect? - CORRECT ANSWER✔✔- Cell-signlaling defect of
fibroblast growth factor (FGF) receptor 3
Marfan's syndrome involves a mutation in what? - CORRECT ANSWER✔✔- Fibrillin gene
Nucleoside + phosphate= ? - CORRECT ANSWER✔✔- Nucleotide
Adenine and Guanine are in what type of nucleic acid? - CORRECT ANSWER✔✔- Purines
Cytosine, Uracil and Thyamine arein what kind of nucleic acid? - CORRECT ANSWER✔✔-
Pyrimidines
Xanthine, hypoxanthine and uric acid are all what type of base? - CORRECT ANSWER✔✔-
Purine
How many hydrogen bonds are found between Guanine and Cytosine? - CORRECT
ANSWER✔✔- 3
Chargaff's ruledictates that the percent of adenine in a DNA molecule is = to the % of _____
in a DNA molecule. - CORRECT ANSWER✔✔- thyamine
What is the rate limiting step in Purine de novo synthesis? - CORRECT ANSWER✔✔-
PRPP step via glutamin PRPP amidotranferase
PRPP amidotransferase inhibited by what downstream products in purine synthesis? -
CORRECT ANSWER✔✔- IMP, GMP, AMP and puring analogs Allopurinola and 6-
mercaptopurine
,What are the required cofactors for purine de novo synthesis? - CORRECT ANSWER✔✔-
THF, glutamine, glycine, aspartate, CO2
Name two crucial enzymes involved in purine salvage pathways - CORRECT ANSWER✔✔-
hypoxanthine Phosoribosyltransferaase (HGPRT) anf Adenosine Deaminase.
HGPRT converts guanine to ______ and hypoxanthine to _______. - CORRECT
ANSWER✔✔- GMP; IMP
Allopurinol and 6-mercaptopurine are purine analogs that inhibit ________. - CORRECT
ANSWER✔✔- PRPP amidotransferase
Allopurinol is used for the treatment of chronic gout because it __________. - CORRECT
ANSWER✔✔- Decreases uric acid levels by blocking xanthine oxidase with converts
hypoxanthing to xanthine and then to uric acid
Lesch-Nyhan is a X-lined recessive disorder due to __________. - CORRECT
ANSWER✔✔- absence of HGPRT--thus patients are unable to salvage purines leading to
excessive de novov synthesis which then leads to excess uric acid production.
The presentation of retardation, cerebral palsy, slef-mutiliation, gout and "crystals in diaper"
and self-muilation is most consistent with ________. - CORRECT ANSWER✔✔- Lesch-
Nyahan Syndrome
What is the treatment for Lesch-Nyhan syndrome? - CORRECT ANSWER✔✔- Allopurinol
(inhibits xanthine oxidase in the purine salvage pathway, thus reducing excesss production of
uric acid)
What disorder is associated with hyperuricenmis either due to overproduction or
underexcretion of uric acis and is charcterized by sodium urate crystal deposits in the joints
and soft tissues? - CORRECT ANSWER✔✔- Gout
What are some causes of uric acid overproduction in aquired gout? - CORRECT
ANSWER✔✔- Leukemia, alcoholism, myelopproliferative syndrom, multiple myeloma,
hemolysis, neoplasia, psoriasis
, What drugs are associated with urate underexcretion in aquired gout? - CORRECT
ANSWER✔✔- Aspirin, diuretics, alcohol
What is podagra? - CORRECT ANSWER✔✔- Gout of the great toe
Monoarticular arthirits of distal joints often with a history of hyperuricemia percipiatated by a
sudden change in urate levels (due to large meals, alcohol) is characteristic of ______ and can
eventually lead to the formation of _______. - CORRECT ANSWER✔✔- gout; nodular
tophi (urate crystals surrounded by fibrous connective tissue) located around the joints and
Achilles tendon.
How is gout diagnosed? - CORRECT ANSWER✔✔- Detection of negatively bifringent
crystals from articular tap, arthritis and hyperuricemia
What is the treatment for Gout? - CORRECT ANSWER✔✔- For chronic-allopurinol to
lower uric acid levels but NOT for acute treatment. For aute treatment decrease pain and
inflammation with colchicines and NSAIDS and avoidance of large meals and ETOH
What is colchicine used for and how does it work? - CORRECT ANSWER✔✔- Acute Gout.
It prevents neutrophil and leukocyte migration into the joint by binding tubulin, depolarizing
microtubules and interefering with motility and degranulation. Note: Indomethacin is more
commonly used due to less side effects
SCID (Severe Combined T and B Immunodeficieny) is an autsomal recessive disorder cause
by a deficiency in what enzyme? - CORRECT ANSWER✔✔- Adenosine deaminse
How does a deficeincy in adenosine deaminase cause SCID? - CORRECT ANSWER✔✔-
W/ a deficiency in adenosidne deaminase (impt enzyme involved purine synthesis) causes the
build up of ATP and dATP which in turn inhibit ribonucleotide reductase thus preventing
DNA synthesis and decreasing lymphocyte count.
Children with no plasma cells or B or T lymphocytes on CBC and no thymus and recurrent
infections (esp. Candida and Pneumocystis jiroveci) are likely to have _______. - CORRECT
ANSWER✔✔- SCID
ACTUAL Exam Questions and CORRECT
Answers
Achondroplasia involves what defect? - CORRECT ANSWER✔✔- Cell-signlaling defect of
fibroblast growth factor (FGF) receptor 3
Marfan's syndrome involves a mutation in what? - CORRECT ANSWER✔✔- Fibrillin gene
Nucleoside + phosphate= ? - CORRECT ANSWER✔✔- Nucleotide
Adenine and Guanine are in what type of nucleic acid? - CORRECT ANSWER✔✔- Purines
Cytosine, Uracil and Thyamine arein what kind of nucleic acid? - CORRECT ANSWER✔✔-
Pyrimidines
Xanthine, hypoxanthine and uric acid are all what type of base? - CORRECT ANSWER✔✔-
Purine
How many hydrogen bonds are found between Guanine and Cytosine? - CORRECT
ANSWER✔✔- 3
Chargaff's ruledictates that the percent of adenine in a DNA molecule is = to the % of _____
in a DNA molecule. - CORRECT ANSWER✔✔- thyamine
What is the rate limiting step in Purine de novo synthesis? - CORRECT ANSWER✔✔-
PRPP step via glutamin PRPP amidotranferase
PRPP amidotransferase inhibited by what downstream products in purine synthesis? -
CORRECT ANSWER✔✔- IMP, GMP, AMP and puring analogs Allopurinola and 6-
mercaptopurine
,What are the required cofactors for purine de novo synthesis? - CORRECT ANSWER✔✔-
THF, glutamine, glycine, aspartate, CO2
Name two crucial enzymes involved in purine salvage pathways - CORRECT ANSWER✔✔-
hypoxanthine Phosoribosyltransferaase (HGPRT) anf Adenosine Deaminase.
HGPRT converts guanine to ______ and hypoxanthine to _______. - CORRECT
ANSWER✔✔- GMP; IMP
Allopurinol and 6-mercaptopurine are purine analogs that inhibit ________. - CORRECT
ANSWER✔✔- PRPP amidotransferase
Allopurinol is used for the treatment of chronic gout because it __________. - CORRECT
ANSWER✔✔- Decreases uric acid levels by blocking xanthine oxidase with converts
hypoxanthing to xanthine and then to uric acid
Lesch-Nyhan is a X-lined recessive disorder due to __________. - CORRECT
ANSWER✔✔- absence of HGPRT--thus patients are unable to salvage purines leading to
excessive de novov synthesis which then leads to excess uric acid production.
The presentation of retardation, cerebral palsy, slef-mutiliation, gout and "crystals in diaper"
and self-muilation is most consistent with ________. - CORRECT ANSWER✔✔- Lesch-
Nyahan Syndrome
What is the treatment for Lesch-Nyhan syndrome? - CORRECT ANSWER✔✔- Allopurinol
(inhibits xanthine oxidase in the purine salvage pathway, thus reducing excesss production of
uric acid)
What disorder is associated with hyperuricenmis either due to overproduction or
underexcretion of uric acis and is charcterized by sodium urate crystal deposits in the joints
and soft tissues? - CORRECT ANSWER✔✔- Gout
What are some causes of uric acid overproduction in aquired gout? - CORRECT
ANSWER✔✔- Leukemia, alcoholism, myelopproliferative syndrom, multiple myeloma,
hemolysis, neoplasia, psoriasis
, What drugs are associated with urate underexcretion in aquired gout? - CORRECT
ANSWER✔✔- Aspirin, diuretics, alcohol
What is podagra? - CORRECT ANSWER✔✔- Gout of the great toe
Monoarticular arthirits of distal joints often with a history of hyperuricemia percipiatated by a
sudden change in urate levels (due to large meals, alcohol) is characteristic of ______ and can
eventually lead to the formation of _______. - CORRECT ANSWER✔✔- gout; nodular
tophi (urate crystals surrounded by fibrous connective tissue) located around the joints and
Achilles tendon.
How is gout diagnosed? - CORRECT ANSWER✔✔- Detection of negatively bifringent
crystals from articular tap, arthritis and hyperuricemia
What is the treatment for Gout? - CORRECT ANSWER✔✔- For chronic-allopurinol to
lower uric acid levels but NOT for acute treatment. For aute treatment decrease pain and
inflammation with colchicines and NSAIDS and avoidance of large meals and ETOH
What is colchicine used for and how does it work? - CORRECT ANSWER✔✔- Acute Gout.
It prevents neutrophil and leukocyte migration into the joint by binding tubulin, depolarizing
microtubules and interefering with motility and degranulation. Note: Indomethacin is more
commonly used due to less side effects
SCID (Severe Combined T and B Immunodeficieny) is an autsomal recessive disorder cause
by a deficiency in what enzyme? - CORRECT ANSWER✔✔- Adenosine deaminse
How does a deficeincy in adenosine deaminase cause SCID? - CORRECT ANSWER✔✔-
W/ a deficiency in adenosidne deaminase (impt enzyme involved purine synthesis) causes the
build up of ATP and dATP which in turn inhibit ribonucleotide reductase thus preventing
DNA synthesis and decreasing lymphocyte count.
Children with no plasma cells or B or T lymphocytes on CBC and no thymus and recurrent
infections (esp. Candida and Pneumocystis jiroveci) are likely to have _______. - CORRECT
ANSWER✔✔- SCID
