Biochemistry USMLE step 1: Updated Solution: Guaranteed A+ Guide Solution

histones are rich in which 2 AA's (Ans- lysine & argenine Barr bodies (what, type of chromatin) (Ans- inactive X chromosomes heterochromatin (highly condensed, sterically inaccessible) less condensed, transcriptionally active, sterically accessible chromatin (Ans- euchromatin DNA methylation at CpG islands (Ans- represses transcription "CpG Methylation makes DNA Mute" DNA methylation (what is methylated and why?) (Ans- template strand cytosine and adenine are methylated during replication --> mismatch repair enzymes can distinguish between old and new strands Histone methylation (Ans- usually reversibly represses DNA transcription (can activate depending on location) "histone Methylation Mostly makes DNA Mute" Histone acetylation (Ans- relaxes DNA coiling --> permits transcription "histone Acetylation makes DNA Active"