USMLE Biochemistry

• This groups give DNA a (-) charge

  Phosphate Group
• Lysine and Arginine 


  Both gives histone a (+) charge
• In _____, DNA condenses to form chromosomes.

  Mitosis
• DNA and Histone Synthesis occurs during what phase?

  S phase
• This have their own DNA?

  Mitochondria
• Heterochromatin

  • Condensed, Darker, Inactive and Inaccessible
  • Increase Methylation; Decrease Acetylation
• Euchromatin

  • Truly transcribed
  • Expressed, Less Condensed, Lighter, Active and Accessible
• DNA methylation 


  changes expression of DNA segments without changing sequence.
• Gene promoter of methylation

  CpG
• CpG


  silences/represses gene transcription
• DNA Methylation

  • Genomic Imprinting
  • X-chromosome Inactivation
  • Repression of transposable elements
  • Aging
  • Carcinogenesis
• Histone Methylation

  • Causes reversible transcriptional suppression but can activate depending on methyl group location
• Histone acetylation

  • Active
  • Removal of histone's (+) charge --> relaxes DNA coiling --> Increases transcription
• Histone Deacetylation

  • Removal of acetyl group --> tightened DNA coiling --> Decreases transcription