BIOCHEMISTRY USMLE STEP 1 STUDY GUIDE 2024/2025 WITH QUESTIONS AND COMPLETE SOLUTION

BIOCHEMISTRY USMLE STEP 1 STUDY GUIDE 2024/2025 WITH QUESTIONS AND COMPLETE SOLUTION histones are rich in which 2 AA's - (ANSWER)lysine & argenine Barr bodies (what, type of chromatin) - (ANSWER)inactive X chromosomes heterochromatin (highly condensed, sterically inaccessible) less condensed, transcriptionally active, sterically accessible chromatin - (ANSWER)euchromatin DNA methylation at CpG islands - (ANSWER)represses transcription "CpG Methylation makes DNA Mute" DNA methylation (what is methylated and why?) - (ANSWER)template strand cytosine and adenine are methyated during replication --> mismatch repair enzymes can distinguish between old and new strands Histone methylation - (ANSWER)usually reversibly represses DNA transcription (can activate depending on location) "histone Methylation Mostly makes DNA Mute" Histone acetylation - (ANSWER)relaxes DNA coiling --> permits transcription "histone Acetylation makes DNA Active" function of methylation and acetylation - (ANSWER)change DNA transcription activity methylation mutes acetylation activates purines (which, ring number) - (ANSWER)A, G 2 rings PUR As Gold pyrimidines (which, ring number) - (ANSWER)C, T, U 1 ring CUT the PY (pie is a single circle)