8.4.2 DNA Methylation and Histone Modification

• DNA methylation typically occurs at cytosine
• Is DNA methylation an epigenetic mechanism?

  Yes
• What is the function of DNMT1?

  Maintains existing methylation
• DNA methylation regulates gene activity without altering the DNA sequence
• DNMT3A and DNMT3B are involved in de novo methylation
• Which DNMT is involved in maintenance methylation?

  DNMT1
• DNMT1 is involved in maintaining existing methylation patterns.

  True
• What chemical group is added to DNA during methylation?

  Methyl group
• Order the steps in the process of DNA methylation.

  1️⃣ DNMTs recognize CpG islands

  2️⃣ DNMTs transfer methyl groups from SAM

  3️⃣ 5-methylcytosine is created
• What is DNMT1 responsible for during DNA replication?

  Maintaining methylation patterns
• Maintenance Methylation copies existing methylation patterns from the parent DNA strand.

  True
• DNMT3A and DNMT3B guide cell differentiation during early embryonic development.


  True
• Acetylation of histones generally activates gene transcription.

  True
• HDACs repress gene transcription by closing chromatin.


  True
• Acetylation allows transcription factors to access DNA more easily.

  True
• Methylation of promoter regions represses gene transcription.


  True
• What is the modified base created during DNA methylation?

  5-methylcytosine
• DNA methylation typically occurs at CpG islands.

  True
• Which DNMT maintains existing methylation patterns?

  DNMT1
• DNMT1 ensures the methylation state is passed on to daughter cells during DNA replication.


  True
• Match the type of methylation with its purpose:

  De Novo Methylation ↔️ Establishes new methylation patterns

  Maintenance Methylation ↔️ Copies existing methylation patterns
• Acetylation of histones generally activates gene transcription.

  True
• What is the effect of acetylation on gene transcription?

  Activates gene transcription
• Histone modifications provide an additional layer of epigenetic regulation beyond DNA methylation.

  True
• What is the effect of histone acetylation on chromatin structure?

  Loosens chromatin structure
• Which enzyme is often involved in phosphorylating histones?

  Kinases
• Histone demethylases (HKDMases) reverse the effects of histone methylation.


  True
• What type of mechanism is DNA methylation considered?

  Epigenetic mechanism
• Which enzymes carry out DNA methylation?

  DNA methyltransferases (DNMTs)
• DNA methylation can only repress gene expression.

  False
• Steps of DNA methylation

  1️⃣ DNMTs recognize specific CpG islands

  2️⃣ DNMTs transfer a methyl group from SAM to cytosine

  3️⃣ 5-methylcytosine is formed
• Match the DNMT type with its function:

  DNMT1 ↔️ Maintains existing methylation patterns

  DNMT3A ↔️ Establishes new methylation patterns

  DNMT3B ↔️ Involved in early development
• What effect does methylation of promoter regions have on gene transcription?

  Represses gene transcription
• What are histone modifications?

  Chemical changes to histones
• Steps of histone modification

  1️⃣ Histone acetyltransferases (HATs) add acetyl groups

  2️⃣ Chromatin structure loosens

  3️⃣ Gene transcription is activated
• Histone modifications are chemical alterations to histone proteins that can change chromatin structure and gene expression without altering DNA sequence
• Methylation always activates gene transcription.

  False
• Order the following histone modifying enzymes by their function on gene expression:

  1️⃣ HATs activate transcription

  2️⃣ HDACs repress transcription

  3️⃣ HKMTs can activate or repress depending on site

  4️⃣ HKDMases reverse methylation effects
• Histone Demethylases (HKDMases) reverse the effects of histone methylation.


  True
• What does DNA methylation repress in gene regulation?

  Transcription factors binding