Biochemistry USMLE step 1 Review Course 2023.

Biochemistry USMLE step 1 Review Course nes 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) thymine vs uracil - ANSWER thymine has a methyl, found in DNA deamination of cytosine --> uracil, found in RNA base pair with 3 H-H bonds (and consequences) - ANSWER G-C G-C is stronger than A-T (2 H-H) inc G-C content --> inc melting temperature of DNA amino acids necessary for purine synthesis - ANSWER GAG + THF glycine aspartate glutamine