Chromatin
Encyclopedia
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
and meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
and prevent DNA damage, and to control gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
and DNA replication. The primary protein components of chromatin are histone
Histone
In biology, histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation...
s that compact the DNA. Chromatin is only found in eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
: prokaryotic cells have a very different organization of their DNA which is referred to as a genophore
Nucleoid
The nucleoid is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. The genome of prokaryotic organisms generally is a circular, double-stranded...
(a chromosome without chromatin).
The structure of chromatin depends on several factors. The overall structure depends on the stage of the cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...
: during interphase
Interphase
Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division. In preparation for cell division, it increases its size and makes a copy of its DNA...
the chromatin is structurally loose to allow access to RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
polymerases that transcribe and replicate the DNA. The local structure of chromatin during interphase depends on the genes present on the DNA: DNA coding genes that are actively transcribed ("turned on") are more loosely packaged and are found associated with RNA polymerases (referred to as euchromatin
Euchromatin
Euchromatin is a lightly packed form of chromatin that is rich in gene concentration, and is often under active transcription. Unlike heterochromatin, it is found in both cells with nuclei and cells without nuclei...
) while DNA coding inactive genes ("turned off") are found associated with structural proteins and are more tightly packaged (heterochromatin
Heterochromatin
Heterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin...
). Epigenetic chemical modification of the structural proteins in chromatin also alter the local chromatin structure, in particular chemical modifications of histone proteins by methylation
Methylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
and acetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
. As the cell prepares to divide, i.e. enters mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
or meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, the chromatin packages more tightly to facilitate segregation of the chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s during anaphase
Anaphase
Anaphase, from the ancient Greek ἀνά and φάσις , is the stage of mitosis or meiosis when chromosomes move to opposite poles of the cell....
. During this stage of the cell cycle this makes the individual chromosomes in many cells visible by optical microscope
Optical microscope
The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the...
.
In general terms, there are three levels of chromatin organization:
- DNA wraps around histone proteins forming nucleosomeNucleosomeNucleosomes are the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a histone protein core. This structure is often compared to thread wrapped around a spool....
s; the "beads on a string" structure (euchromatinEuchromatinEuchromatin is a lightly packed form of chromatin that is rich in gene concentration, and is often under active transcription. Unlike heterochromatin, it is found in both cells with nuclei and cells without nuclei...
). - Multiple histones wrap into a 30 nm fibre consisting of nucleosome arrays in their most compact form (heterochromatinHeterochromatinHeterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin...
). - Higher-level DNA packaging of the 30 nm fibre into the metaphase chromosome (during mitosisMitosisMitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
and meiosisMeiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
).
There are, however, many of cells which do not follow this organisation. For example spermatozoa and avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
red blood cells have more tightly packed chromatin than most eukaryotic cells and trypanosomatid protazoa do not condense their chromatin into visible chromosomes for mitosis.
During interphase
The structure of chromatin during interphaseInterphase
Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division. In preparation for cell division, it increases its size and makes a copy of its DNA...
is optimized to allow easy access of transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
and DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
factors to the DNA while compacting the DNA into the nucleus. The structure varies depending on the access required to the DNA. Genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
that require regular access by RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
require the looser structure provided by euchromatin.
Change in structure
Chromatin undergoes various forms of change in its structure. Histone proteins, the foundation blocks of chromatin, are modified by various post-translational modification to alter DNA packing. Acetylation results in the loosening of chromatin and lends itself to replication and transcription. When certain residues are methylated they hold DNA together strongly and restrict access to various enzymes. A recent study showed that there is a bivalentBivalent chromatin
Bivalent chromatin is chromatin that contains both activating and repressing epigenetic modifications in the same area. Activating chromatin modifications increase the accessibility of the chromatin to RNA polymerase, where repressing modifications decrease the accessibility to RNA polymerase...
structure present in the chromatin: methylated lysine residues at location 4 and 27 on histone 3. It is thought that this may be involved in development; there is more methylation of lysine 27 in embryonic cells than in differentiated cells, whereas lysine 4 methylation positively regulates transcription by recruiting nucleosome remodeling enzymes and histone acetylases.
Polycomb-group proteins
Polycomb-group proteins
Polycomb-group proteins are a family of proteins first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place...
play a role in regulating genes through modulation of chromatin structure.
For additional information see Histone modifications in chromatin regulation and RNA polymerase control by chromatin structure
DNA structure
The vast majority of DNA within the cell is the normal DNA structure. However in nature DNA can form three structures, A-, B- and Z-DNA
Z-DNA
Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the double helix winds to the left in a zig-zag pattern...
. A and B chromosomes are very similar, forming right-handed helices, while Z-DNA is a more unusual left-handed helix with a zig-zag phosphate backbone. Z-DNA is thought to play a specific role in chromatin structure and transcription because of the properties of the junction between B- and Z-DNA.
At the junction of B- and Z-DNA one pair of bases is flipped out from normal bonding. These play a dual role of a site of recognition by many proteins and as a sink for torsional stress from RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
or nucleosome binding.
The nucleosome and "beads-on-a-string"
- Main articles: NucleosomeNucleosomeNucleosomes are the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a histone protein core. This structure is often compared to thread wrapped around a spool....
, ChromatosomeChromatosomeA chromatosome is essentially a nucleosome with one bound linker histone. See: nucleosome and chromatin.-Details:A chromatosome consists of a histone octamer, one molecule of linker histone, for example, Histone H1 and 166bp of DNA. The linker histone is a binding agent, acting like a finger...
and HistoneHistoneIn biology, histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation...
Linker dna
Linker DNA is double-stranded DNA in between two nucleosome cores that, in association with histone H1, holds the cores together. Linker DNA is seen as the string in the "beads and string model," which is made by using an ionic solution on the chromatin. Linker DNA connects to histone H1 and...
, a far shorter arrangement than pure DNA in solution.
In addition to the core histones, there is the linker histone, H1, which contacts the exit/entry of the DNA strand on the nucleosome. The nucleosome core particle, together with histone H1, is known as a chromatosome. Nucleosomes, with about 20 to 60 base pairs of linker DNA, can form, under non-physiological conditions, an approximately 10 nm "beads-on-a-string" fibre. (Fig. 1-2). .
The nucleosomes bind DNA non-specifically, as required by their function in general DNA packaging. There are, however, large DNA sequence preferences that govern nucleosome positioning. This is due primarily to the varying physical properties of different DNA sequences: For instance, adenosine and thymine
Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...
are more favorably compressed into the inner minor grooves. This means nucleosomes can bind preferentially at one position approximately every 10 base pairs (the helical repeat of DNA)- where the DNA is rotated to maximise the number of A and T bases that will lie in the inner minor groove. (See mechanical properties of DNA
Mechanical properties of DNA
In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA and RNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its...
.)
30 nm chromatin fibre
This level of chromatin structure is thought to be the form of euchromatin
Euchromatin
Euchromatin is a lightly packed form of chromatin that is rich in gene concentration, and is often under active transcription. Unlike heterochromatin, it is found in both cells with nuclei and cells without nuclei...
, which contains actively transcribed genes. EM studies have demonstrated that the 30 nm fibre is highly dynamic such that it unfolds into a 10 nm fiber ("beads-on-a-string") structure when transversed by an RNA polymerase engaged in transcription.
A stable 30 nm fibre relies on the regular positioning of nucleosomes along DNA. Linker DNA is relatively resistant to bending and rotation. This makes the length of linker DNA critical to the stability of the fibre, requiring nucleosomes to be separated by lengths that permit rotation and folding into the required orientation without excessive stress to the DNA.
In this view, different length of the linker DNA should produce different folding topologies of the chromatin fiber. Recent theoretical work, based on electron-microscopy images
of reconstituted fibers support this view.
Spatial organization of chromatin in the cell nucleus
The layout of the genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
within the nucleus is not random - specific regions of the genome have a tendency to be found in certain spaces. Specific regions of the chromatin are enriched at the nuclear membrane, while other regions are bound together by protein complexes. The layout of this is not, however, well characterised apart from the compaction of one of the two X chromosomes in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
s into the Barr body
Barr body
A Barr body is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z...
. This serves the role of permanently deactivating these genes, which prevents females getting a 'double dose'
Dosage compensation
Dosage compensation, also known as Ohno's Hypothesis, is a hypothetical genetic regulatory mechanism which operates to equalize the phenotypic expression of characteristics determined by genes on the X chromosome so that they are equally expressed in the human XY male and the XX female. In 2006,...
relative to male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
s. The extent to which the inactive X is actually compacted is a matter of some controversy.
Chromatin and bursts of transcription
Fluctuations between open and closed chromatin may contribute discontinuity of transcription, or transcriptional burstingTranscriptional bursting
Transcriptional bursting, also known as transcriptional pulsing, is a fundamental property of genes from bacteria to humans. Transcription of genes, the process which transforms the stable code written in DNA into the mobile RNA message can occur in "bursts" or "pulses"...
. Other factors are probably involved, such as the association and dissociation of transcription factor complexes with chromatin. The phenomenon, as opposed to simple probabilistic models of transcription, can account for the high variability in gene expression occurring between cells in isogenic populations.
Metaphase chromatin
Metaphase
Metaphase, from the ancient Greek μετά and φάσις , is a stage of mitosis in the eukaryotic cell cycle in which condensed & highly coiled chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells...
structure of chromatin differs vastly to that of interphase
Interphase
Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division. In preparation for cell division, it increases its size and makes a copy of its DNA...
. It is optimised for physical strength and manageability, forming the classic chromosome structure seen in karyotype
Karyotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
s. The structure of the condensed chromosome is thought to be loops of 30 nm fibre to a central scaffold of proteins. It is, however, not well characterised.
The physical strength of chromatin is vital for this stage of division to prevent shear damage to the DNA as the daughter chromosomes are separated. To maximise strength the composition of the chromatin changes as it approaches the centromere, primarily through alternative histone H1 anologues.
It should also be noted that, during mitosis, while most of the chromatin is tightly compacted, there are small regions that are not as tightly compacted. These regions often correspond to promoter regions of genes that were active in that cell type prior to entry into cromitosis. The lack of compaction of these regions is called bookmarking
Bookmarking
In genetics and epigenetics, bookmarking is a biological phenomenon believed to function as an epigenetic mechanism for transmitting cellular memory of the pattern of gene expression in a cell, throughout mitosis, to its daughter cells...
, which is an epigenetic mechanism believed to be important for transmitting to daughter cells the "memory" of which genes were active prior to entry into mitosis. This bookmarking
Bookmarking
In genetics and epigenetics, bookmarking is a biological phenomenon believed to function as an epigenetic mechanism for transmitting cellular memory of the pattern of gene expression in a cell, throughout mitosis, to its daughter cells...
mechanism is needed to help transmit this memory because transcription ceases during mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
.
Chromatin: alternative definitions
- Simple and concise definition: Chromatin is DNA plus the proteins (and RNA) that package DNA within the cell nucleus.
- A biochemists’ operational definition: Chromatin is the DNA/protein/RNA complex extracted from eukaryotic lysed interphase nuclei. Just which of the multitudinous substances present in a nucleus will constitute a part of the extracted material will depend in part on the technique each researcher uses. Furthermore, the composition and properties of chromatin vary from one cell type to the another, during development of a specific cell type, and at different stages in the cell cycle.
- The DNA + histone = chromatin definition: The DNA double helix in the cell nucleus is packaged by special proteins termed histones. The formed protein/DNA complex is called chromatin. The structural entity of chromatin is the nucleosome.
Alternative chromatin organisations
During metazoan spermiogenesisSpermiogenesis
Spermiogenesis is the final stage of spermatogenesis, which sees the maturation of spermatids into mature, motile spermatozoa. The spermatid is more or less circular cell containing a nucleus Golgi apparatus, centriole and mitochondria...
, the spermatid
Spermatid
The spermatid is the haploid male gametid that results from division of secondary spermatocytes. As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte....
's chromatin is remodelled into a more spaced-packaged, widened, almost crystal-like structure. This process is associated with the cessation of transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
and involves nuclear
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
protein exchange. The histones are mostly displaced, and replaced by protamine
Protamine
Protamines are small, arginine-rich, nuclear proteins that replace histones late in the haploid phase of spermatogenesis and are believed essential for sperm head condensation and DNA stabilization. They may allow for denser packaging of DNA in spermatozoon than histones, but they must be...
s (small, arginine
Arginine
Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that codify for arginine during...
-rich proteins).
Nobel Prizes
The following scientists were recognized for their contributions to chromatin research with Nobel PrizeNobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
s:
| Year | Who | Award |
|---|---|---|
| 1910 | Albrecht Kossel Albrecht Kossel Ludwig Karl Martin Leonhard Albrecht Kossel was a German biochemist and pioneer in the study of genetics. He was awarded the Nobel Prize for Physiology or Medicine in 1910 for his work in determining the chemical composition of nucleic acids, the genetic substance of biological cells.Kossel... (University of Heidelberg) |
Nobel Prize in Physiology or Medicine Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will... "in recognition of the contributions to our knowledge of cell chemistry made through his work on proteins, including the nucleic substances" |
| 1933 | Thomas Hunt Morgan Thomas Hunt Morgan Thomas Hunt Morgan was an American evolutionary biologist, geneticist and embryologist and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries relating the role the chromosome plays in heredity.Morgan received his PhD from Johns Hopkins University in zoology... (California Institute of Technology) |
Nobel Prize in Physiology or Medicine Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will... "for his discoveries concerning the role played by the chromosome in heredity" |
| 1962 | Francis Crick Francis Crick Francis Harry Compton Crick OM FRS was an English molecular biologist, biophysicist, and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson... , James Watson James D. Watson James Dewey Watson is an American molecular biologist, geneticist, and zoologist, best known as one of the co-discoverers of the structure of DNA in 1953 with Francis Crick... and Maurice Wilkins Maurice Wilkins Maurice Hugh Frederick Wilkins CBE FRS was a New Zealand-born English physicist and molecular biologist, and Nobel Laureate whose research contributed to the scientific understanding of phosphorescence, isotope separation, optical microscopy and X-ray diffraction, and to the development of radar... (MRC Laboratory of Molecular Biology, Harvard University and London University respectively) |
Nobel Prize in Physiology or Medicine Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will... "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material" |
| 1982 | Aaron Klug Aaron Klug Sir Aaron Klug, OM, PRS is a Lithuanian-born British chemist and biophysicist, and winner of the 1982 Nobel Prize in Chemistry for his development of crystallographic electron microscopy and his structural elucidation of biologically important nucleic acid-protein complexes.-Biography:Klug was... (MRC Laboratory of Molecular Biology) |
Nobel Prize in Chemistry Nobel Prize in Chemistry The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,... "for his development of crystallographic electron microscopy and his structural elucidation of biologically important nucleic acid-protein complexes" |
| 1993 | Roberts and Sharp | Nobel Prize in Physiology "for their independent discoveries of split genes" |
| 2006 | Roger Kornberg (Stanford University) | Nobel Prize in Chemistry Nobel Prize in Chemistry The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,... "for his studies of the molecular basis of eukaryotic transcription" |
See also
- Histone-Modifying EnzymesHistone-Modifying EnzymesThe packaging of the eukaryotic genome into highly condensed chromatin makes it inaccessible to the factors required for gene transcription, DNA replication, recombination and repair. Eukaryotes have developed intricate mechanisms to overcome this repressive barrier imposed by the chromatin...
- ChromatidChromatidA chromatid is one of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division . They are called sister chromatids so long as they are joined by the centromeres...
- Salt-and-pepper chromatinSalt-and-pepper chromatinIn pathology, salt-and-pepper chromatin, also salt-and-pepper nuclei and stippled chromatin, refers to cell nuclei that demonstrate granular chromatin ....
- Transcriptional burstingTranscriptional burstingTranscriptional bursting, also known as transcriptional pulsing, is a fundamental property of genes from bacteria to humans. Transcription of genes, the process which transforms the stable code written in DNA into the mobile RNA message can occur in "bursts" or "pulses"...
Other references
- Cooper, Geoffrey M. 2000. The Cell, 2nd edition, A Molecular Approach. Chapter 4.2 Chromosomes and Chromatin.
- Corces, V. G. 1995. Chromatin insulators. Keeping enhancers under control. Nature 376:462-463.
- Cremer, T. 1985. Von der Zellenlehre zur Chromosomentheorie: Naturwissenschaftliche Erkenntnis und Theorienwechsel in der frühen Zell- und Vererbungsforschung, Veröffentlichungen aus der Forschungsstelle für Theoretische Pathologie der Heidelberger Akademie der Wissenschaften. Springer-Vlg., Berlin, Heidelberg.
- Elgin, S. C. R. (ed.). 1995. Chromatin Structure and Gene Expression, vol. 9. IRL Press, Oxford, New York, Tokyo.
- Gerasimova, T. I., and V. G. Corces. 1996. Boundary and insulator elements in chromosomes. Current Op. Genet. and Dev. 6:185-192.
- Gerasimova, T. I., and V. G. Corces. 1998. Polycomb and Trithorax group proteins mediate the function of a chromatin insulator. Cell 92:511-521.
- Gerasimova, T. I., and V. G. Corces. 2001. CHROMATIN INSULATORS AND BOUNDARIES: Effects on Transcription and Nuclear Organization. Annu Rev Genet 35:193-208.
- Gerasimova, T. I., K. Byrd, and V. G. Corces. 2000. A chromatin insulator determines the nuclear localization of DNA [In Process Citation]. Mol Cell 6:1025-35.
- Ha, S. C., K. Lowenhaupt, A. Rich, Y. G. Kim, and K. K. Kim. 2005. Crystal structure of a junction between B-DNA and Z-DNA reveals two extruded bases. Nature 437:1183-6.
- Pollard, T., and W. Earnshaw. 2002. Cell Biology. Saunders.
- Saumweber, H. 1987. Arrangement of Chromosomes in Interphase Cell Nuclei, p. 223-234. In W. Hennig (ed.), Structure and Function of Eucaryotic Chromosomes, vol. 14. Springer-Verlag, Berlin, Heidelberg.
- Sinden, R. R. 2005. Molecular biology: DNA twists and flips. Nature 437:1097-8.
- Van Holde KE. 1989. Chromatin. New York: Springer-VerlagSpringer Science+Business Media- Selected publications :* Encyclopaedia of Mathematics* Ergebnisse der Mathematik und ihrer Grenzgebiete * Graduate Texts in Mathematics * Grothendieck's Séminaire de géométrie algébrique...
. ISBN 0-387-96694-3. - Van Holde, K., J. Zlatanova, G. Arents, and E. Moudrianakis. 1995. Elements of chromatin structure: histones, nucleosomes, and fibres, p. 1-26. In S. C. R. Elgin (ed.), Chromatin structure and gene expression. IRL Press at Oxford University Press, Oxford.
External links
- Chromatin, Histones & Cathepsin; PMAP The Proteolysis MapThe Proteolysis MapThe Proteolysis MAP is an integrated web resource focused on proteases.-Rationale:PMAP is to aid the protease researchers in reasoning about proteolytic networks and metabolic pathways.-History and funding:...
-animation - Recent chromatin publications and news
- Protocol for in vitro Chromatin Assembly