Epigenetics

• What is the enzyme responsible for DNA methylation?

  DNMT
• The methyl group in DNA methylation is transferred from SAM
• 5mC is found in all cytosine sequences in DNA.

  False
• Methylation of a 'C' in a CG combination turns gene expression off
• After DNA replication, a CG combination results in hemi-methylation.
• Steps in maintaining full DNA methylation after replication

  1️⃣ DNA replication produces hemi-methylated CG

  2️⃣ DNMT completes methylation on the new strand

  3️⃣ Full methylation ensures gene silencing
• What are regions of high CG density in DNA called?

  CpG islands
• During embryonic development, genes are turned off by methylation
• What happens to CpG islands during passive DNA demethylation?

  Become unmethylated
• Active DNA demethylation involves TET enzymes.
• Steps in active DNA demethylation

  1️⃣ 5mC is modified to 5hmC

  2️⃣ 5hmC is converted to 5fC

  3️⃣ 5fC is modified to 5caC

  4️⃣ DNA repair enzymes complete the process
• What happens to tumour suppressor genes in cancer due to DNA methylation?

  Hypermethylation
• Histone acetylation leads to gene expression.
• Histone acetyltransferases (HATs) add acetyl groups to lysine residues on histones
• Match the histone core proteins with their descriptions:

  H2A ↔️ Core protein that can be acetylated

  H3 ↔️ Core protein involved in chromatin structure
• What type of histone modification can lead to either gene expression or repression?

  Methylation
• Histone phosphorylation reduces the positive charge of histones.
• Which enzyme reverses histone ADP-ribosylation?

  ADP-ribose-protein hydrolase
• Histone SUMOylation and ubiquitylation involve the addition of small protein-like molecules to lysine
• What is the role of piRNAs in epigenetics?

  Silencing transposons
• Genomic imprinting follows classic Mendelian laws of inheritance.

  False
• Epigenetics involves modifications that change phenotype but not genotype
• What is the importance of genomic imprinting in gene expression?

  Specific gene expression
• Epigenetics can be influenced by age and lifestyle.
• Match the types of epigenetics with their descriptions:

  DNA Methylation ↔️ Gene silencing by 5mC

  Histone Modification ↔️ Changes in chromatin structure

  Genomic Imprinting ↔️ Allele-specific gene silencing