Chapter 19 Chapter 19 Eukaryotic genomes organization, regulation and evolution http //www studiodaily com/main/searchlist/6850 html “The Inner life of the Cell” Gene expression Is altered in response[.]
Chapter 19 Eukaryotic genomes: organization, regulation and evolution http://www.studiodaily.com/main/searchlist/6 850.html “The Inner life of the Cell” Gene expression… • Is altered in response to environmental changes, both internal and external • Is influenced by the structure of chromatin – Heterochromatin is highly compacted and is not transcribed – Euchromatin is less compacted and available for transcription • Is most often regulated at the transcription stage • Differential gene expression (cell differentiation) is the result of genes being turned “on” or “off” in different cells having the same genome • Only 1.5% of human DNA codes for proteins Chromatin structure… • Eukaryotic DNA associates with many histone proteins that form complex structures – the mass of histones = the mass of DNA • Histones – highly conserved, small, basic proteins that shape the 1st level of chromatin structure: – The high [ ]’s of arganine and lysine make them +ly charged – Of the types (H1,H2A,H2B,H3,H4) all but H1 are found in the nucleosome, the basic unit of DNA packing – Are evolutionarily conserved – Only leave DNA briefly during replication • Interphase chromatin is attached to the nuclear lamina to keep chromosomes from tangling Eukaryotic DNA structure • DNA + histones form nucleosomes (10nm fiber) • Nucleosomes coil to form chromatin fiber (30nm fiber) • 30nm fiber folds into looped domains (300nm fiber) • Chromatin condenses further to form the metaphase chromosome (highly compacted 1400 nm) CONTROL POINTS in eukaryotic gene expression: • Regulation of chromatin structure: histone acetylation and DNA methylation • Transcription of the gene: transcription initiation • RNA Processing: alternative RNA splicing • mRNA export: • mRNA degradation: polyA tail, miRNA, RNAi • Translation of mRNA: regulatory proteins block initiation of translation • Polypeptide processing: cleavage, modification and transport • Protein Degradation: ubiquitin/proteasome activity • Stages in which eukaryotic gene expression can be regulated are represented by the colored boxes Regulation of chromatin structure: • Histone modification – acetyl groups added to histone tails relax chromatin and promote transcription • DNA methylation can inactivate genes and be inherited by offspring– genomic imprinting works this way! Control of gene expression in eukaryotes: an overview • http://highered.mcgraw-hill.com/olc/dl/120 080/bio31.swf The eukaryotic gene consists of • the gene + RNA polymerase + a promoter • Control elements – non-coding DNA that regulates transcription by binding to certain proteins Distal elements called enhancers are very important • Transcription factors: – General transcription factors result in low RNA production – Specific transcription factors can promote high levels of transcription They may be: • Activators – protein that stimulates transcription • Repressors – proteins that inhibit gene expression – Activators and repressors may alter chromatin structure, thereby further influencing gene expression ... overview • http://highered.mcgraw-hill.com/olc/dl /12 0 080/bio 31. swf The eukaryotic gene consists of • the gene + RNA polymerase + a promoter • Control elements – non-coding DNA that regulates transcription... basic proteins that shape the 1st level of chromatin structure: – The high [ ]’s of arganine and lysine make them +ly charged – Of the types (H1,H2A,H2B,H3,H4) all but H1 are found in the nucleosome,... co-expressed because they have the same control elements that are activated by the same chemical signals Regulation of transcription • http://wps.aw.com/bc_campbell_biology_7 /0,9854 ,17 0497 5-, 00.html