8.4.2 DNA Methylation and Histone Modification

• What does epigenetic control of gene expression involve?

  Modifications to DNA and proteins
• Epigenetic modifications are heritable and can be influenced by environmental
• DNA methylation typically occurs at CpG sites.
• What is the primary effect of DNA methylation on gene expression?

  Suppresses gene expression
• Histone acetylation typically enhances gene expression.
• Histone methylation always suppresses gene expression.

  False
• What is DNA methylation?

  Addition of methyl groups to cytosine
• DNA methyltransferase enzymes catalyze DNA methylation.


  True
• DNA methyltransferases add a methyl group to cytosine bases at CpG sites.
• DNA methylation suppresses gene expression by inhibiting transcription factor binding.

  True
• What is histone modification?

  Addition or removal of chemical groups to histones
• Steps of how histone acetylation enhances gene expression

  1️⃣ Addition of acetyl groups to histone tails

  2️⃣ Neutralization of positive charge on histones

  3️⃣ Weakened interaction with DNA

  4️⃣ Relaxation of chromatin structure

  5️⃣ Increased transcription factor access

  6️⃣ Gene expression is enhanced
• What are the key differences between DNA methylation and histone modification?

  Mechanism and location
• Match the biological process with the epigenetic mechanisms involved:

  Embryonic development ↔️ DNA methylation and histone modification regulate cell differentiation

  Genomic imprinting ↔️ DNA methylation silences one copy of genes

  X-chromosome inactivation ↔️ DNA methylation maintains the silenced state

  Cancer ↔️ Aberrant DNA methylation and histone modifications silence tumor suppressor genes
• Epigenetic modifications change the underlying DNA sequence.

  False
• What is DNA methylation?

  Addition of methyl group to cytosine
• DNA methyltransferases add methyl groups to cytosine bases at CpG sites.


  True
• Describe the steps by which DNA methylation inhibits gene expression:

  1️⃣ Methyl group addition by DNMTs at CpG sites

  2️⃣ Interference with transcription factor binding

  3️⃣ Recruitment of methyl-binding proteins

  4️⃣ Chromatin condensation
• What does histone modification involve?

  Addition or removal of chemical groups
• What is the primary effect of DNA methylation on chromatin structure?

  Condensation
• DNA methylation typically occurs at CpG sites.
• What is the primary effect of DNA methylation on gene expression?

  Suppression
• Steps of how DNA methylation inhibits gene expression

  1️⃣ Methyl group addition by DNA methyltransferases at CpG sites

  2️⃣ Methyl groups block transcription factors from binding to DNA

  3️⃣ Methylated DNA recruits methyl-binding proteins

  4️⃣ Chromatin condenses, making DNA less accessible

  5️⃣ Gene expression is suppressed
• Acetylation of histones enhances gene expression by promoting open chromatin.
• Histone modifications dynamically regulate gene expression by altering chromatin structure.


  True
• DNA methylation typically occurs at CpG sites, while histone modification occurs on histone tails.