USMLE STEP 1- BIOCHEMISTRY UPDATED STUDY GUIDE
QUESTIONS AND CORRECT ANSWERS
Histones are rich in which 2 amino acids? Lysine
Arginine
What histone protein is responsible for binding to the H1
nucleosome and to the "linker" DNA thereby stabilizing
the chromatin fiber?
When does DNA and histone synthesis occur in the cell S-phase
cycle?
Will the following be increased or decreased or neutral methylation increased
in heterochromatin? acetylation decreased
methylation
acetylation
Which two bases are methylated in DNA replication on Cytosine
the template strand in prokaryotes? Adenine
(Protip: this is done so the mismatch repair enzymes can distinguish between
old and new strands)
Where does DNA methylation occur in eukaryotes? CpG islands
(Protip: this represses transcription)
Deamination of cytosine will produce.... Uracil
Deamination of adenine will produce.... Guanine
Methylation of uracil will produce.... Thymine
What amino acids are necessary for purine synthesis? Glycine
Aspartate
Glutamine
What enzyme does Leflunomide inhibit? inhibits dihydroorotate dehydrogenase
What will be the general effect of Leflunomide? (results in increased carbamoyl1-P concentration and a blockage of the early
steps of pyrimidine base production)
, What enzyme does Methotrexate inhibit? Dihydrofolate reductase in humans
What will be the general effect of Methotrexate? Causes a decrease in deoxythmidine monophosphate (dTMP)
What enzyme does trimethorpim inhibit? Dihydrofolate reductase in bacteria
What enzyme does pyrimethamine inhibit? Dihydrofolate reductase in protozoa
What enzyme does 5-Fluorouracil inhibit? Thymidylate synthase
What will be the general effect of 5-FU? Decreased conversion of dUMP to dTMP
What will be the general effect of 5-mercaptopurine? Inhibit de novo purine synthesis
What will be the general effect of azathioprine? Inhibit de novo purine synthesis
(Protip: This is the prodrug for 5-mercaptopurine.)
What enzyme will be inhibited by Mycophenolate? Inosine monophosphate dehydrogenase
What will be the general effect of Mycophenolate? Disruption of purine synthesis
What enzyme will be inhibited by Ribavirin? Inosine monophosphate dehydrogenase
What will be the general effect of Ribavirin? Disruption of purine synthesis
What enzyme will be inhibited by Hydroxyurea? Ribonucleotide reductase
What will be the general effect of Hydroxyurea? (Protip: can't add deoxy to sugars without this enzyme)
Disruption of both purine and pyrimidine synthesis
QUESTIONS AND CORRECT ANSWERS
Histones are rich in which 2 amino acids? Lysine
Arginine
What histone protein is responsible for binding to the H1
nucleosome and to the "linker" DNA thereby stabilizing
the chromatin fiber?
When does DNA and histone synthesis occur in the cell S-phase
cycle?
Will the following be increased or decreased or neutral methylation increased
in heterochromatin? acetylation decreased
methylation
acetylation
Which two bases are methylated in DNA replication on Cytosine
the template strand in prokaryotes? Adenine
(Protip: this is done so the mismatch repair enzymes can distinguish between
old and new strands)
Where does DNA methylation occur in eukaryotes? CpG islands
(Protip: this represses transcription)
Deamination of cytosine will produce.... Uracil
Deamination of adenine will produce.... Guanine
Methylation of uracil will produce.... Thymine
What amino acids are necessary for purine synthesis? Glycine
Aspartate
Glutamine
What enzyme does Leflunomide inhibit? inhibits dihydroorotate dehydrogenase
What will be the general effect of Leflunomide? (results in increased carbamoyl1-P concentration and a blockage of the early
steps of pyrimidine base production)
, What enzyme does Methotrexate inhibit? Dihydrofolate reductase in humans
What will be the general effect of Methotrexate? Causes a decrease in deoxythmidine monophosphate (dTMP)
What enzyme does trimethorpim inhibit? Dihydrofolate reductase in bacteria
What enzyme does pyrimethamine inhibit? Dihydrofolate reductase in protozoa
What enzyme does 5-Fluorouracil inhibit? Thymidylate synthase
What will be the general effect of 5-FU? Decreased conversion of dUMP to dTMP
What will be the general effect of 5-mercaptopurine? Inhibit de novo purine synthesis
What will be the general effect of azathioprine? Inhibit de novo purine synthesis
(Protip: This is the prodrug for 5-mercaptopurine.)
What enzyme will be inhibited by Mycophenolate? Inosine monophosphate dehydrogenase
What will be the general effect of Mycophenolate? Disruption of purine synthesis
What enzyme will be inhibited by Ribavirin? Inosine monophosphate dehydrogenase
What will be the general effect of Ribavirin? Disruption of purine synthesis
What enzyme will be inhibited by Hydroxyurea? Ribonucleotide reductase
What will be the general effect of Hydroxyurea? (Protip: can't add deoxy to sugars without this enzyme)
Disruption of both purine and pyrimidine synthesis
