Chromatin Structure
Chromatin StructureDr. Carol S. Newlonnewlon@umdnj.eduICPH E250P
DNA Packaging Is aFormidable Challenge Single DNA molecule in human chromosomeca. 5 cm long Diploid genome contains ca. 2 meters of DNA Nucleus of human cell ca. 5 µm in diameter Human metaphase chromosome ca. 2.5 µmin length 10,000 to 20,000 packaging ratio required
Overview ofDNAPackaging
Packaging in Interphase Nucleus
Chromatin Composition Complex of DNA and histones in 1:1mass ratio Histones are small basic proteins– highly conserved during evolution– abundance of positively charged aa’s(lysine and arginine) bind negativelycharged DNA Four core histones: H2A, H2B, H3, H4in 1:1:1:1 ratio Linker histone: H1 in variable ratio
Chromatin Fibers11-nm fiber beads nucleosomescompaction 2.5Xlow ionic strength bufferH1 not required30-nm fiber physiological ionicstrength (0.15 M KCl) compaction 42X H1 required
Micrococcal Nuclease Digestion ofChromatin
Stochiometry of Histones and DNA 146 bp DNA ca.100 kDa 8 histones ca108 kDa mass ratio ofDNA:protein1:1
Structure of Core Nucleosome1.65 left handed turns of DNA around histone octamer
Histone Structure
Assembly of a Histone Octamer
Nucleosomes Are Dynamic
Chromatin RemodelingLarge complexes of 10 proteinsUse energy of ATP hydrolysis to partially disrupthistone-DNA contactsCatalyze nucleosome sliding or nucleosome removal
30-nm Chromatin Fiber Structure?
Models for H1 and Core HistoneTails in Formation of 30-nm Fiber
Histone Tails
Covalent Modifications of Histone Tails ControlChromatin FunctionAcetylation (K)Phosphorylation (S)Methylation (K, R)Ubiquitinylation (K)Sumoylation (K)
Enzymes that Modify Histones Histone acetyltransferases (HATs)Histone deacetylases (HDACs)Histone methyl transferases (HMTs)Histone kinases
Meanings of Histone ‘Code’
Transcriptional RegulatorsModify Histone Acetylation
Transcriptional Regulators ModifyHistone Acetylation
Histone Code Readers Code readercomplexes recognizeparticular marks onchromatin Attract additionalprotein complexesthat executebiological function
Formation of HeterochromatinSilences Gene Expression Heterochromatin-regions ofdarkly staining chromatin ineukaryotic nuclei Transcriptionally silent DNA Centromeres, telomeres areheterochromatic Genes near heterochromatinshow metastable expressionpatterns– position effect variegation in flies– telomere position effects in yeast
Formation of Heterochromatin inMammalian Cells Requires specificmodification:Histone H3 lysine 9trimethylation(H3K9Me3) by H3K9HMT Heterochromatinprotein 1 (HP1)
Boundary Elements PreventSpread of Heterochromatin
Histone Variants Have SpecialFunctions
Centromeres Are Heterochromaticand Contain SpecializedNucleosome
Higher OrderPackaging
Higher Order Packaging(300-nm fiber)Mechanism of looping unknown
Mitotic Chromosome Condensation Depends on SMC (structural maintenance ofchromosomes) proteins, which are conservedfrom bacteria to man– Condensins (SMC2 & SMC4)– Cohesins (SMC1 & SMC3)– large proteins with coiled-coiled domains andATPase domains
Model of Cohesin in MitoticChromosomes
Molecular Basis of CohesionCohesinNasmyth 2002 Science 297:559
histone-DNA contacts Catalyze nucleosome sliding or nucleosome removal. . (structural maintenance of chromosomes) proteins, which are conserved from bacteria to man . ATPase domains. Model of Cohesin in Mitotic Chromosomes. Molecular Basis of Cohesion Cohesin Nasmyth 2002 Science 297:559. Title: Microsoft PowerPoint - Chromatin Structure .
Journal of Experimental Botany Advance Access published February 4, 2014 at University of Florida on March 28, 2014 . around which 146 bp of DNA are wrapped, forming the basic unit of chromatin. The structure of chromatin is regu- . (Pandey et al., 2002). All of these families of
structural details of the most condensed chromatin structures are still largely debated.1 3 At the lowest levels of chromatin structure (0.1 1 Kb), much is known, namely, that 147 bp of double stranded DNA is wrapped tightly around 8 core histone proteins (H2A, H2B, H3, and H4), to form the nucleosome. These nucleosomes, in
I. DNA, Chromosomes, Chromatin, and Genes DNA blueprint of life (has the instructions for making an organism) Chromatin uncoiled DNA Chromosome coiled DNA You have 46 chromosomes or 23 pairs in the nucleus of each body cell. o 23 from mom and 23 from dad Gene a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc); a gene is a stretch of .
Chromatin–composed of DNA and histone proteins Condensed chromatin –contains tightly coiled strands of DNA Extended chromatin –contains uncoiled strands of DNA DNA's genetic code is copied onto mRNA (transcription)
Histone is the core protein component of the chromatin com-plex; it provides a structural backbone for the DNA to wrap around at regular intervals to form the chromatin. The nu-cleosome represents the first level of chromatin organization. It is composed of two copies each of histones H2A, H2B, H3, and H4, assembled in an octameric core with DNA
Arrays of nucleosomes condense into higher order chromatin fibers (Fig. 4.6.3.). Despite over 2 decades of investigation the structure of the “30nm” chromatin fiber is not known. This may be due to irregularity or instability of the structure. This level of structure has been implicated in mecha
Structure Function chromatin –mix of DNA and protein nucleoplasm fills nucleus nucleolus –denser region containing RNA, protein, chromatin nuclear envelope –double membrane separates from rest of the cell control centre for entire cell stores and replicates genetic information (DNA) Cytoplasm
Grade 2 Indiana Academic Standards 2014 3 . READING: Literature. There are three key areas found in the Reading: Literature section for grades 6-12: Key Ideas and Textual Support, Structural Elements and Organization, and Synthesis and Connection of Ideas. By demonstrating the skills listed in each section, students should be able to meet the Learning Outcome for Reading: Literature. Learning .
