CHAPTER 16 Flashcards
(24 cards)
Epigenetics
the study of mechanisms that lead to changes in gene expression that:
-can be passed from cell to cell
-reversible
-do not involve a change in the sequence of DNA
Epigenetic inheritance
involves epigenetic changes that are passed from parent to offspring, like X-chromosome inactivation and genomic imprinting
types of molecular change underlie epigenetic regulation
- DNA methylation
- Chromatin remodeling
- Covalent histone modification
- Localization of histone variants
- Feedback loops
Cis-epigenetic changes; where is it maintained and how many genes does it impact?
maintained only at a specific site, may affect only one copy of a gene but not
the other copy
Trans-epigenetic changes; where is it maintained and how many genes does it impact?
maintained by diffusible factors, such as transcription factors, affect both copies of a gene
General categories of epigenetic gene regulation
programmed developmental change and environmental agents
programmed developmental change
- Genomic imprinting (silencing of a paternal or maternal allele)
- X chromosome inactivation (Barr body)
- Cell differentiation (specialization
environmental agents
- Temperature (cold temperatures required for future growth)
- Diet (royal jelly and queen bees)
- Toxins (tobacco smoke alters DNA methylation)
Chromatin
Chromatin is the complex of DNA, proteins, and non-coding RNAs that package chromosomal DNA in eukaryotic cells.
Chromatin’s Basic Unit
It is the nucleosome, consisting of DNA wrapped around an octamer of histone proteins.
Two types of chromatin
- Euchromatin
- Heterochromatin
Euchromatin
-non-compacted
-transcriptionally active
Heterochromatin
-highly compacted
-gene expression inhibited
What is the role of heterochromatin in gene regulation?
Heterochromatin silences gene expression, prevents transposable element movement, and inhibits viral proliferation.
What is the difference between constitutive and facultative heterochromatin?
-Constitutive heterochromatin is permanently heterochromatic at the same location in all cell types
-Facultative heterochromatin varies among cell types and developmental stages
What are the characteristics of constitutive heterochromatin?
-Stable formation
-high condensation
-found near centromeres/telomeres
-consists of repeat sequences
-highly methylated
-specific histone modifications
What are the characteristics of facultative heterochromatin?
-Reversible formation
-located at various sites
-involves LINE-type repeats
-methylation at CpG islands
-shares some histone modifications with constitutive heterochromatin.
What molecular events lead to heterochromatin formation?
-Histone post-translational modifications (PTMs)
-Protein binding to nucleosomes,
-Chromatin remodeling
-DNA methylation
-Binding of non-coding RNAs
How is heterochromatin maintained during cell division?
Epigenetic marks like DNA methylation and histone modifications are preserved in daughter cells, ensuring the inheritance of heterochromatin patterns.
Genomic Imprinting
A form of gene regulation where only one allele of a gene is expressed, depending on the parent from whom it is inherited.
X-chromosome inactivation
A process during early embryonic development in female mammals where one X chromosome is randomly inactivated to achieve dosage compensation.
What role does the Trithorax group (TrxG) protein play in development?
TrxG is involved in gene activation
-regulating epigenetic changes during cell differentiation
What role does the Polycomb group (PcG) protein play in development?
PcG is involved in gene repression
-regulating epigenetic changes during cell differentiation
How do environmental agents influence epigenetics?
Dietary factors and toxins can cause epigenetic changes, as seen in examples like the Agouti gene in mice and the development of honeybee queens due to royal jelly.
