Cycle 11 Flashcards
📝 Question: What is the definition of epigenetics?
✅ Answer: Epigenetics is the study of changes in gene expression caused by mechanisms other than changes in the underlying DNA sequence, such as DNA methylation and histone modifications.
📝 Question: What is the difference between the genome and the epigenome?
Genome refers to the complete set of DNA, including all genes. It remains mostly unchanged throughout life.
Epigenome consists of chemical tags (e.g., methyl and acetyl groups) on the DNA or histones that regulate gene expression. It is dynamic and can change due to life experiences and environmental factors.
📝 Question: Why do identical twins have the same genome but different epigenomes as they age?
✅ Answer: Identical twins start with the same genome, but their epigenomes diverge due to different life experiences, environmental exposures, and lifestyle choices. Differences in DNA methylation and histone modifications can be detected as early as two years old.
_________: Increased methylation turns genes off by preventing transcription factor binding.
Hypermethylation
📝 Question: How does DNA methylation occur?
Process: DNA methyltransferases (DNMTs) add a methyl (-CH3) group to cytosine bases at CpG regions.
________: Decreased methylation turns genes on by allowing transcription factors to bind.
Hypomethylation
📝 Question: How does DNA demethylation occur, and what is its effect on gene expression?
Process: The TET enzyme removes methyl groups from cytosine.
Effects: Demethylation activates transcription by allowing transcription factors to bind to the promoter.
📝 Question: How does histone acetylation occur, and what effect does it have on gene expression?
Process: Histone acetyltransferases (HATs) add acetyl (-COCH3) groups to lysine residues on histone tails.
Effects: Acetylation neutralizes lysine’s positive charge, loosening DNA binding, converting heterochromatin into euchromatin, and activating gene transcription.
📝 Question: How does histone deacetylation occur, and what effect does it have on gene expression?
Process: Histone deacetylases (HDACs) remove acetyl groups from histones.
Effects: Deacetylation restores lysine’s positive charge, tightening DNA binding, converting euchromatin into heterochromatin, and repressing gene transcription.
📝 Question: What is the difference between heterochromatin and euchromatin?
Heterochromatin: Tightly packed DNA, transcriptionally inactive, associated with deacetylated histones and hypermethylated DNA.
Euchromatin: Loosely packed DNA, transcriptionally active, associated with acetylated histones and hypomethylated DNA.
📝 Question: What enzymes are responsible for DNA methylation and demethylation?
DNA methyltransferases (DNMTs) add methyl groups to cytosine.
TET enzymes remove methyl groups from cytosine.
📝 Question: What enzymes are responsible for histone acetylation and deacetylation?
Histone Acetyltransferases (HATs) add acetyl groups, increasing transcription.
Histone Deacetylases (HDACs) remove acetyl groups, decreasing transcription.
📝 Question: How does DNA methylation get established and maintained?
De Novo Methylation: DNMT3A and DNMT3B add methyl groups to unmethylated cytosines in response to new experiences.
Maintenance Methylation: DNMT1 copies methylation patterns onto newly synthesized DNA strands during replication.
📝 Question: How can epigenetic modifications be inherited across generations?
✅ Answer: Epigenetic tags (e.g., DNA methylation patterns) can be passed from parents to offspring through gametes. This is called transgenerational epigenetic inheritance and is influenced by life experiences, diet, and environment.
❓ What did twin studies reveal about the epigenome?
✅ Monozygotic twins show epigenetic differences as early as 3 years old, which become more pronounced by age 50.
❓ What is “epigenetic drift”?
✅ Epigenetic modifications that accumulate with age, leading to differences in gene expression even in genetically identical twins.
❓ How does the epigenome change in response to experiences?
✅ Experiences can alter epigenetic tags, affecting gene expression and behavior.
❓ How does maternal care affect stress responses in rats?
Highly nurturing mothers (lick/groom more) → Less anxiety, high GR (glucocorticoid receptor) expression
Low nurturing mothers → Highly anxious pups, high corticosterone levels, low GR expression
❓ What epigenetic change was observed in low-nurtured pups?
✅ Hypermethylation of the Nr3C1 gene promoter, leading to inactivation of GR transcription.
❓ What happened when pups were switched between nurturing and non-nurturing mothers?
✅ Their epigenetic markers changed, demonstrating that early-life experiences can alter the epigenome.
❓ How was epigenetic modification experimentally induced?
✅ When a highly nurtured rat was injected with a drug that added methyl tags, it became anxious.
❓ What is transgenerational epigenetic inheritance?
✅ Epigenetic changes acquired in one generation can be stably passed to offspring through sperm and eggs.
❓ How can environmental exposures affect DNA function?
✅ Early-life experiences permanently impact gene expression, which can then be inherited by offspring.
❓ How were baby monkeys used to study epigenetics?
✅ Baby monkeys were randomly assigned to be raised by their biological mothers or surrogates (humans or objects).
