Biochemistry NBME Exam Questions and
Complete Solutions Updated
Histones
beads on a string (analbeads)
-rich in arginine and lysine
-heterochromatin is condensed
-euchromatin is transcribed
-cytosine and adenine are methylated in DNA transcription allowing for mismatch
enzymes in PROKARYOTES
-histone methylation inactivates transcription of DNA. acetylation activates it
nucleotides
pure as gold are purines (adenine and guanine)
-2 rings
pyrimidines are Cut The Pie
-uracil subbed in for thymine in RNA
purine and pyrimidine synthesis
PRPP is common link
-6-MP blocks purine
-5 FU, hydroxyurea inhibit pyrimidine synthesis
, -methotrexate and trimethoprim inhibit dihydrofolate reducatase.methotraxate is for
humans (chemo), trimethoprim is for bacteria (sulfas)
orotic aciduria
pyrimidine disease. not in breakdown tho bc pyrimidines are soluble.
AR disease.
-cannot convert orotic acid to UMP bc UMP synthase is messed up
purine salvage diseases
purines need to be broken down to uric acid.
-SCIDS is adenosine deaminase deficiency - inhibition of ribonucleotide reductase
which prevents DNA synthesis and increases lymphocyte count.
lesch-nyhan syndrome
gout on steroids. deficient HGPRT.
-X-linked recessive
DNA pol III
only in prokaryotes. 5' to 3' synthesis and proofreads 3' to 5' exonuclease.
DNA pol I
only in prokaryotes. Degrades RNA primer (5'-3' exonuclease) and replaces it with DNA.
nucleotide excision repair
mutated in xeroderma pigemtosum which is a AR disease.
base excision repair
important in toxic deamination.
mismatch repair
mutated in HNPCC (non-polypoid colon cancer)
For DS DNA mutations - nonhomologous end joining
mutated in ataxia telangiectasia
DNA RNA Protein
DNA and RNA synthesized 5' to 3', read 3' to 5'.
-mRNA is read 5' to 3' and protein is synthesized from N-terminus to C-terminus
RNA polymerases
RNA pol I is rRNA
RNA pol II is mRNA
Complete Solutions Updated
Histones
beads on a string (analbeads)
-rich in arginine and lysine
-heterochromatin is condensed
-euchromatin is transcribed
-cytosine and adenine are methylated in DNA transcription allowing for mismatch
enzymes in PROKARYOTES
-histone methylation inactivates transcription of DNA. acetylation activates it
nucleotides
pure as gold are purines (adenine and guanine)
-2 rings
pyrimidines are Cut The Pie
-uracil subbed in for thymine in RNA
purine and pyrimidine synthesis
PRPP is common link
-6-MP blocks purine
-5 FU, hydroxyurea inhibit pyrimidine synthesis
, -methotrexate and trimethoprim inhibit dihydrofolate reducatase.methotraxate is for
humans (chemo), trimethoprim is for bacteria (sulfas)
orotic aciduria
pyrimidine disease. not in breakdown tho bc pyrimidines are soluble.
AR disease.
-cannot convert orotic acid to UMP bc UMP synthase is messed up
purine salvage diseases
purines need to be broken down to uric acid.
-SCIDS is adenosine deaminase deficiency - inhibition of ribonucleotide reductase
which prevents DNA synthesis and increases lymphocyte count.
lesch-nyhan syndrome
gout on steroids. deficient HGPRT.
-X-linked recessive
DNA pol III
only in prokaryotes. 5' to 3' synthesis and proofreads 3' to 5' exonuclease.
DNA pol I
only in prokaryotes. Degrades RNA primer (5'-3' exonuclease) and replaces it with DNA.
nucleotide excision repair
mutated in xeroderma pigemtosum which is a AR disease.
base excision repair
important in toxic deamination.
mismatch repair
mutated in HNPCC (non-polypoid colon cancer)
For DS DNA mutations - nonhomologous end joining
mutated in ataxia telangiectasia
DNA RNA Protein
DNA and RNA synthesized 5' to 3', read 3' to 5'.
-mRNA is read 5' to 3' and protein is synthesized from N-terminus to C-terminus
RNA polymerases
RNA pol I is rRNA
RNA pol II is mRNA
