Transcript EPIGENETICS
EPIGENETICS Definition The study of reversible and heritable alterations in gene expression that occur independently of DNA sequence. Processes Methylation Acetylation Phosphorylation Ubiquitylation Sumolyation Epigenotype Definition “Expression patterns” that act like molecular switches affecting which genes are turned on and which are turned off. Modification Positive A natural process that affects gene expression essential to many functions during growth and development. Negative Malfunctioning can lead to illnesses, change in behaviors, and other health indicators. EPIGENOTYPE MODIFICATION DNA Methylation Purpose Methyl groups direct enzymes to start signals on genes. Process S-adenosyl-L-Methionine transfers a -CH3 to cytosine. Result Methylated Cytosine suppresses transcription Unmethylated Cytosine allows transcription Importance Silencing of “junk’ DNA Regulation of gene expression Genomic Imprinting Methylation patterns are different from cell to cell EPIGENOTYPE MODIFICATION Histone Modification Purpose Acetylation of histones will allow access to genes for transcription. Process Histones are acetylated and deacetylated on lysine residues in the N-terminal tail and on the surface of the nucleosome core Result Euchromatin Acetylation opens up DNA for transcription Heterochromatin Deacetylation closes DNA for transcription Regulation Histone Code Heterochromatin Gene repression DNA Nucleosome Euchromatin Gene transcription Histone acetylation HATs: CBP, p300, PCAF etc COACTIVATORS RNA polymerase II Transcription factor Histone deacetylation HDAC1-11 NCoR, NuRD, mSin3, etc COREPRESSORS mRNA Acetylation of lysines Regulation of gene expression by histone acetylation EPIGENOTYPE MODIFICATION Genomic Imprinting Definition Epigenetic modifications that are erased and then reset during the creation of eggs and sperm (gametogenesis). Process Methylation of regulatory regions on a gene Purpose Marking a gene as being inherited from either the father or mother. “Parent of Origin Specific” GENOMIC IMPRINTING Demethylation Purpose Turn off genes for fertilization Leave genes for Mitosis Timing Zygote formation Remethylation Purpose Reset the genes of somatic cells for differentiation Timing Third week of human development when blastocyst becomes the gastrula. Maintenance Methylation Purpose Set genes for various stages of life DNA Fingerprinting Definition Examination of DNA sequences using probes of noncoding regions of DNA. Method Gel Electrophoresis Process 1) DNA samples are cut by restriction enzymes. 2) Samples are placed in wells of Chamber 3) Electrical input will move different fragment sizes at varying speeds 4) Fragments can be compared for similarity. GEL ELECTROPHORESIS GEL ELECTROPHORESIS GEL ELECTROPHORESIS