R5 epigenetics Flashcards
What is epigenetics ?
the study of heritable changes in gene expression and gene function that cannot be explained by changes in the DNA sequences
Usually activation or deactivation of DNA by other molecules
What is the epigenome ?
The particular set of molecules that a cell has in order to behave differently to the rest, they act as DNA markers.
Different specialised cells have the same genome but different epigenomes
epigenomes are different in identical twins and develop over time
What is DNA methylation in respects to epigenetics ?
present in prokaryotes and eukaryotes, transfer of methyl groups on the CG sequences of DNA.
Established by a writer enzyme (changes the DNA but not the sequence)
Removed by an eraser protein
Methylation in the promoter region inhibits binding of the transcription factors so the gene is inactivated
Methylation recognised by the reader proteins: these promote or inhibit the recruitment of other proteins like transcription proteins
methylation needs to be re-established after the semi-conservative replication. Writer proteins need to methylate the other strand on the hemi-methylated DNA.
What is the use of epigenetic marks ?
they allow the cell to remember what type of cell they are and derived from, the epigenome is maintained throughout mitotic inheritance.
Describe histone modification?
They can be acetylated, methylated, phosphorylated and ubiquitylated by writers.
this can expose or hide entire new code for the readers.
What is H3K9ac ?
Histone 3 proteins, lysine (K) residue at position 9 gets acetylated
the DNA is negative, the acetyl group (-COCH3) neutralises the positive charge
looser DNA, means more accessible to transcriptional machinery
What is H3K27me3?
Histone 3, Lysine (K) at position 27, gets tri-methylated
Promotes more condensation (heterochromatin) leading to silencing.
silences flowering genes during winter generations in plants, is inherited from parental to offspring
How is histone modifications inherited ?
Nucleosomes are dis-assembled ahead of the replication fork
new histones added from the cytosolic pool, marks on the parental histones recruit readers/writers to deposit marks on the new histones.
What needs to happen in order for epigenetics to be transmitted across generations ?
marks need to be present in the germline (plants have a defined germline early on unlike animals)
marks need to be retained in absence of exposure to trigger (that caused the marker to attach in the first place)
eraser proteins remove marks in animal gametes, if erasure not complete we get transgenerational inheritance.
What does phosphate groups do to histones ?
loosens the DNA allowing for transcription
What generation would prove trans-generational inheritance of epigenetic marks ?
F1 won’t show it as they are present (as seeds) during the stress, F2 and F3 show a defined germline
What is the advantage to inheriting epigenetic marks ?
The future offspring are less affected by the stress
allowing for altered transcriptional response to the stress.
What is the epigenetics behind queen and worker bees ?
The absence of worker jelly maintains the queen-specific gene expression
phenolics are required to produce a queen
What is ploidy ?
The number of chromosomes in a cell
determines the sex of bees, males are haploids
How does methylation affected the splicing of genes
High methylation - skipping of exons and longer protein produced
Low methylation - exons retentions - a shorter prtein is produced, STOP codon in the exon, produces a queen bee
