Genetics Notes.docx - Video 12 Chromatin Remodeling...

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Video 12 Chromatin Remodeling - Chromatin remodeled to increase or decrease transcription - Chromosomes aren’t randomly distributed, they have a specific territory in the nucleus - This depends on gene density o Ex: chrsm 18 is found on the edge cuz it has few genes o Chrsm 19 is gene rich and is found in center of nucleus - Center of nucleus is rich with proteins that help with transcription - Spaces between chromosomes that forms network of channels - Channels are large enough to allow molecules needed for transcription, replication, etc. to get through - Cell division disrupts the territories of the chromosomes in the nucleus but by the next interphase, all the chromosomes territories are restored Histones - Even though chromatin are not condensed (diffused) for most of the cell cycle, its still can be … - There are regions of the chromosomes that are highly compacted all throughout the cell cycle - How close nucleosomes are spaced affects access to transcription machinery - The more tightly spaced, the closes nucleosomes are decreases ability to transcribe - Chromatin structure can be divided into 2 types: strong correlation between structure of chromatin & transcription activity o Euchromatin areas of the genome where nucleosomes are more widely spaced o Tend to be gene rich areas o Heterochromatin areas of the genome where nucleosomes are closer together o Gene poor areas (ex: centromere region, and telomeric o areas) lack genes, or genes are repressed Euchromatin o More widely spaced nucleosomes o Allows transcriptional molecules more access to DNA o Most transcriptionally active area located in euchromatin region o Widely spaced also means other molecules have more access to DNA For example, DNase o DNase can cut DNA, therefore, Euchromatin is considered “hypersensitive to DNase”
Heterochromatin o Associated with transcriptional repression o Genetically inactive areas: o Some areas, like centromeres & telomeres DNA remain tightly bound and provide structural, referred to constituent heterochromatin, always remain heterochromatin o Areas that stain intensely o Replicate later in S phase o Faculitive heterochromatin reversable heterochromatin Ex: tissue-specific genes, needs to be turned off and on (on through cell signals that make it remain in Euchromatin structure) - Most inactive genes have nucleosomes that sit on the promoter - They physically prevent binding of transcriptional machineries (Ex: transcriptional factors, RNA Polymerase) - There are times when we need to turn on a gene, so how is access then given? - Through different mechanisms, we can get differences in chromatin structure - Referred to as chromatin remodeling - We can move nucleosomes, or we can loosen binding of DNA nucleosome - We get more access to transcriptional proteins and enzymes that cut DNA -

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