Biochemistry USMLE Step 1
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
Allopurinol and 6-mercaptopurine are purine analogs that inhibit
________. –
,PRPP amidotransferase
Allopurinol is used for the treatment of chronic gout because it
__________. –
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 __________. –
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
________. –
Lesch-Nyahan Syndrome
What is the treatment for Lesch-Nyhan syndrome? –
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? –
Gout
What are some causes of uric acid overproduction in aquired gout? –
Leukemia, alcoholism, myelopproliferative syndrom, multiple
myeloma, hemolysis, neoplasia, psoriasis
What drugs are associated with urate underexcretion in aquired gout?
–
Aspirin, diuretics, alcohol
, What is podagra? –
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 _______. –
gout; nodular tophi (urate crystals surrounded by fibrous connective
tissue) located around the joints and Achilles tendon.
How is gout diagnosed? –
Detection of negatively bifringent crystals from articular tap, arthritis
and hyperuricemia
What is the treatment for Gout? –
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? –
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? –
Adenosine deaminse
How does a deficeincy in adenosine deaminase cause SCID? –
Deficiency in adenosine deaminase (impt enzyme involved purine
synthesis) causes the build up of ATP and dATP which in turn inhibit
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
Allopurinol and 6-mercaptopurine are purine analogs that inhibit
________. –
,PRPP amidotransferase
Allopurinol is used for the treatment of chronic gout because it
__________. –
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 __________. –
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
________. –
Lesch-Nyahan Syndrome
What is the treatment for Lesch-Nyhan syndrome? –
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? –
Gout
What are some causes of uric acid overproduction in aquired gout? –
Leukemia, alcoholism, myelopproliferative syndrom, multiple
myeloma, hemolysis, neoplasia, psoriasis
What drugs are associated with urate underexcretion in aquired gout?
–
Aspirin, diuretics, alcohol
, What is podagra? –
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 _______. –
gout; nodular tophi (urate crystals surrounded by fibrous connective
tissue) located around the joints and Achilles tendon.
How is gout diagnosed? –
Detection of negatively bifringent crystals from articular tap, arthritis
and hyperuricemia
What is the treatment for Gout? –
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? –
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? –
Adenosine deaminse
How does a deficeincy in adenosine deaminase cause SCID? –
Deficiency in adenosine deaminase (impt enzyme involved purine
synthesis) causes the build up of ATP and dATP which in turn inhibit
