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Questions and Answers
What is the primary effect of DNA methylation on gene expression?
Which epigenetic mechanism is best understood according to recent research?
What typically triggers the loss of DNA methylation in fertilized cells?
How do environmental factors influence epigenetic modifications?
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Which type of genes are referred to as housekeeping genes?
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What happens to DNA methyltransferases during the early stages of embryonic development?
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What is transgenerational inheritance in the context of epigenetics?
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What characterizes genetic imprinting?
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What is the role of noncoding RNAs (ncRNAs) or microRNAs (miRNAs) in gene regulation?
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Which statement about CpG dinucleotides is correct?
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What is the process called in which genes are silenced based on parental inheritance?
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What typically characterizes an imprinted allele?
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What syndrome is associated with a deletion on chromosome 15 inherited from the mother?
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Which syndrome is characterized by overgrowth and an increased cancer risk?
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In Russell-Silver syndrome, what is the typical effect on IGF-2?
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Which epigenetic modification can be reversed using pharmaceutical intervention?
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How do methylation patterns in twins typically change as they age?
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In the context of cancer, what happens to methylation densities as tumors progress?
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What effect does fetal alcohol exposure have on the DNA methyltransferases?
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What is a common feature of hypermethylation in relation to cancer development?
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Study Notes
Epigenetic Mechanisms
- Three major epigenetic mechanisms are under investigation: DNA methylation, histone modifications, and noncoding RNAs (ncRNAs).
- DNA methylation involves attachment of a methyl group to cytosine, primarily at CpG dinucleotides.
- Histone modifications alter gene expression by adding chemical groups like methyl and acetyl, impacting transcription.
- Noncoding RNAs, including microRNAs (miRNAs), regulate diverse signaling pathways; their functions are often not fully understood.
- Methylation typically inhibits gene transcription; when heavy methylation occurs, the gene is less likely to be converted to mRNA.
- Environmental factors, such as diet and chemical exposure, can induce epigenetic changes.
- Transgenerational inheritance refers to passing epigenetic modifications to future generations.
Epigenetics and Human Development
- Epigenetic modifications can alter gene expression without changing the DNA sequence.
- Housekeeping genes are essential for cell maintenance and typically remain transcriptionally active, escaping epigenetic silencing.
- Fertilization results in loss of DNA methylation, with most gene loci becoming unmethylated and transcriptionally active.
- DNA methyltransferases reactivation occurs during uterine implantation, establishing cell-lineage-specific marks necessary for organ development.
Genetic Imprinting
- Genetic imprinting leads to some genes being transcriptionally active from one parental allele and inactive from the other.
- Imprinted alleles usually show heavy methylation, while nonimprinted alleles remain unmethylated.
- Prader-Willi syndrome and Angelman syndrome are linked to a deletion on chromosome 15; the disease phenotype depends on the parent's transmission of the deletion.
- Beckwith-Wiedemann syndrome involves IGF-2 overexpression causing overgrowth, contrasted by Russell-Silver syndrome, where reduced IGF-2 leads to growth deficiencies.
Inheritance of Epigenetic States
- Events during prenatal and early life stages can lead to epigenetic changes associated with phenotypic abnormalities and metabolic syndromes.
- Fetal alcohol spectrum disorder may arise from alcohol's repression of DNA methyltransferases during pregnancy.
- Fragile X syndrome shows abnormal methylation gain, while facioscapulohumeral muscular dystrophy is characterized by abnormal methylation loss.
- Ageing twins exhibit increased differences in DNA methylation patterns, contributing to variances in phenotypes.
- Significant lifestyle differences, like smoking, can lead to substantial discrepancies in twins' methylation patterns over time.
Cellular Metabolism
- Strong evidence linking epigenetic changes to human disease risk has been observed in cancer studies.
- As tumors progress, methylation densities decline, potentially activating oncogenes and facilitating the transition from benign neoplasms to malignancy.
- Promoter regions of tumor-suppressor genes often experience hypermethylation, reducing their transcription and tumor inhibition capacity.
- Hypermethylation of miRNA genes is also associated with tumorigenesis.
- Unlike DNA mutations, epigenetic modifications can potentially be reversed with pharmaceutical treatments; for example, 5-azacytidine is a demethylating agent used in leukemia therapy.
Future Directions
- Ongoing research emphasizes the impact of epigenetic states on cell fate determination.
- Epigenetic abnormalities play significant roles in carcinogenesis, with implications for developing new therapies aimed at reversing these epigenetic changes in common diseases.
Studying That Suits You
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Description
Explore the key points of Chapter 03 from Huether's 'Understanding Pathophysiology' focusing on epigenetic mechanisms and their implications in disease. This quiz delves into DNA methylation and histone modifications, providing a deeper understanding of these critical biological processes.
