BS 161 1st Edition Lecture 34 Outline of Last Lecture I. Transcription translationOutline of Current Lecture II. Gene expressionCurrent Lecture-genes within highly packed heterochromatin are usually not expressed-genes in euchromatin are expressed-histone acetylation: acetyl groups are attached to positively charged lysines in histone tails-HAT is enzyme that adds-DHAC is enzyme that removes-the addition of methyl groups (methylation) can condense chromatin-the addition of phosphate groups (phosphorylation) next to a methylated amino acid can loosen chromatin-histone code hypothesis: proposes that specific combinations of modifications help determine chromatin configuration and influence transcription-DNA methylation: the addition of methyl groups to certain bases in DNA-is associated with reduced transcription in some species-can cause long-term inactivation of genes in cellular differentiation-genomic imprinting: methylation regulates expression of either the maternal or paternal allelesof certain genes at the start of development-epigenetic inheritance: the inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence-chromatin-modifying enzymes provide initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery-operons only occur in prokaryotes-control elements: segments of noncoding DNA that help regulate transcription by binding certain proteins-control elements and the proteins they bind are critical to the precise regulation of gene expression in different cell
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