BIOL201 Lecture Notes - Lecture 21: Somatic Cell Nuclear Transfer, Embryonic Stem Cell, Inner Cell Mass
3 Feb 2016
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Document Summary
The process whereby a cell acquires specialized characteristics. As the individual mature there is more and more specialized tissue. Coordinated by expression of a gene or combination of genes. Co-expression of regulatory genes is acquired over time. Sometimes we need just one signal (transcription factor) to activate a lot of genes. Differentiation turns off un-needed dna segments by chromatin packing. Heterochromatin: tightly folded chromatin prevents access by transcription machinery (em- dark image) Euchromatin: looser chromatin that is actively transcribed (visible under em) Chromatin packing relies on modification of histones (methylation, acetylation: all have different impacts on the packing) These modifications are heritable: if a cell is dividing the daughter cells will acquire the same histone modifications and turn off the same genes: Differentiation turns off gene expression by dna methylation. Leads to blocking of promoter region, no transcription. This methylation can be passed on affecting the same regulation of genes: heritable (epigenetic)
