BIOLOGY 172 Lecture Notes - Lecture 23: Histone Methylation, Dna Methyltransferase, Chromatin
Document Summary
Prokaryotic genes are expressed unless it is repressed. Eukaryotic genes are only expressed when they"re turned on . Multicellularity implies a need for differentiation -- different cells w/ different functions (still same dna) Dna binding proteins package dna into chromatin. Tight packing blocks rna polymerase access to dna. Nucleosome - chromatin packaging unit - histone proteins & dna. Histone proteins are positively charged -- attracted to negatively charged phosphate groups. Chromatin must be opened before rna pol can attach to dna. Dnmt (enzyme) adds methyl groups to cytosine. Dnmt leads to tight packaging of chromatin. Modifying proteins around which dna is wrapped. Enzymes add chemical tags to histone tail of amino acids. Hats (enzymes) add acetyl groups to positively charged lysine residues - opens chromatin. Hdacs remove acetyl group - closes chromatin. Remodeling complexes se atp to move nucleosome. Opened-up chromatin allows rna pol to bind to dna to begin transcription.
