LIFE 120 Lecture 30: Chapter 15 Lecture 2 Notes
Document Summary
Eukaryotes: all organisms must regulate which genes are expressed at any given time, adapt to external & internal stimuli. Dna methylation: dna methylation is the addition of methyl groups to certain bases in dna, usually cytosine. Individual genes are usually more heavily methylated in cells where they are not expressed: once methylated, genes usually remain so through successive cell divisions. Operons in prokaryotes: operon, 5 genes in tryptophan operon (trp operon, transcribed as a single mrna from 1 promoter, coordinated by a single on-off (cid:862)switch(cid:863) -- operator, operator (regulatory switch, dna regulatory (cid:862)seg(cid:373)e(cid:374)t(cid:863) i(cid:374) the pro(cid:373)oter. Roles of transcription factors: to initiate transcription, eukaryotic rna polymerase requires the assistance of proteins called transcription factors, general transcription factors are essential for the transcription of all protein- coding genes. In eukaryotes, high levels of transcription of particular genes depend on binding between control elements and specific transcription factors.
