An Introduction to Molecular Biology/Nucleus

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The nucleus was the first organelle to be discovered. The probably oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632 – 1723). He observed a "Lumen", the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still possess nuclei. The nucleus was also described by Franz Bauer in 1804 and in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer. He did not suggest a potential function.






Components of NUCLEUS[edit]

The nucleoskeleton[edit]

The nucleoskeletal framework that remains insoluble after treatment of nuclei with non-ionic detergents, followed by nuclease treatment and high salt extraction to remove chromatin and soluble proteins, is generally termed the nuclear matrix. This nucleoskeleton consists of two parts namely, the nuclear lamina and a network of intricately structured fibres connected to the lamina and distributed throughout the nuclear volume. These highly structured fibre assemblies have been shown to be attached to an underlying network of 10 nm core filaments . The nuclear lamins A, B and C are the major structural components of the peripheral lamina. Additional proteins that connect the lamina to the nuclear envelope and the heterochromatin are clustered at the nuclear periphery. Other nuclear matrix-associated components like hnRNP complexes, newly transcribed full-length mRNA, RNA polymerase I and II, various transcription factors and spliceosomal complexes are positioned on the underlying network of branched 10 nm filaments that is connected to the nuclear lamina . These associations might be dynamic and allow for considerable plasticity in nuclear architecture and function. Furthermore, numerous studies have suggested the presence of an organizing structure such as the nuclear matrix to coordinate the spatial regulation of DNA synthesis. The major candidate proteins that are likely to comprise the nucleoskeleton are lamins and nuclear actin.

1.Nuclear envelope: 

The nuclear envelope (NE) (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus (DNA in particular) from the cytosol (cytoplasm). Many nuclear pores are inserted in the nuclear envelope, which facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm.Nuclear membranes is composed of a lipid bilayer. The outer membrane is continuous with the rough endoplasmic reticulum while the inner nuclear membrane is the primary residence of several inner nuclear membrane proteins. The outer and inner nuclear membrane are fused at the site of nuclear pore complexes. The structure of the membrane also consists of ribosomes.The space between the two membranes that make up the nuclear envelope is called the perinuclear space (also called the perinuclear cisterna, NE Lumen), and is usually about 20 - 40 nm wide.The inner nuclear membrane is connected to the nuclear lamina.[4]

Nuclear envelope breakdown during mitosis

Nuclear envelope breakdown and reassembly in mitosis. At the end of G2, the activation of cyclin-dependent kinases, including CDK1, triggers entry into mitotic prophase. The nuclear membrane breaks down, and the NE-associate proteins either translocate to kinetochores, distribute with the fragmented ER networks, or dissolve in the cytoplasm. During NE reassembly in anaphase, SUN1 and LAP2 first appear around the condensed chromatin, though at different regions. The nuclear lamins then join the nuclear periphery in telophase. This figure illustrates the important roles played by the NE and the nuclear lamina in normal mitosis. Chi et al. Journal of Biomedical Science 2009.[1] During prophase in mitosis, the chromatids begin condensing to form chromosomes, and the nuclear envelope breaks down and is retracted into the mitotic endoplasmic reticulum. At metaphase, the nuclear envelope has been completely disassembled and absorbed by the ER allowing the chromosomes to be put together by spindle fibers attached to each chromosome at the kinetochore. Other eukaryotes such as yeast undergo closed mitosis, where the chromosomes segregate within the nuclear envelope, which then buds as the three daughter cells divide. In the process of mitosis, the nuclear envelope is degraded during prometaphase. Without this step, the nuclear material would be unable to separate into two nuclei, and by extension, two cells. At the end of anaphase however, the chromosomes are now separated, and each set is in its respective half of the parent cell. In order to protect the genetic material, the nuclear membrane must re-form at this stage. This is done using membrane from the endoplasmic reticulum and proteins called lamins that guide the new envelope. (Alberts) Like some of the other organelles in the cell, the endoplasmic reticulum is composed of a phospholipid bilayer. This thin membrane is very flexible, and portions can be pinched off to form new organelles, vesicles, or in this case, nuclei. In 2007, researchers discovered that pieces of the ER break off and merge together to form the nuclear envelope. However, there must be a structural element that brings these vesicles together, because the nucleus is much more structurally complicated than the ER. This element is a layer of lamin between the chromatid and the nuclear envelope itself, known as the lamina. Lamins are long fibrous proteins. In prometaphase, they are phosphorylated (a phosphate group is added), causing the protein to change shape and lose its structural properties. This is what causes the breaking down of the nuclear membrane. However, towards the end of anaphase, the existing lamin is dephosphorylated, and even more is produced. Once the chromosomes have separated, the lamina begins to form again. Sometime at the beginning of mitosis, ends of the endoplasmic reticulum bound to the DNA, using lamin A receptor. (Duband-Goulet and Courvalin) Once the lamina begins to re-form, it forces tubules of ER to form a network across the surface of the chromatid. (Anderson and Hetzer) These tubes eventually are flattened out and merged, forming a solid nuclear membrane. It is not certain what mechanisms cause this to happen. The ER and the LBR eventually detach themselves from the DNA. In a mature cell, the lamina forms a continuous layer just inside the nuclear envelope, and is attached to the nucleus by protein known as emerin.[5]

2.Nuclear pores:


Assembly of the NPC





3.Nuclear lamina:


Architucture of Nuclear Lamina

The nuclear lamina consists of two main components, lamins and nuclear lamin associated membrane proteins. The lamins are type V intermediate filaments which can be categorized as either A-type (lamin A, C) or B-type(lamin B1, B2) according to homology in sequence, biochemical properties and cellular localization during the cell cycle. Type V intermediate filaments differ from cytoplasmic intermediate filaments in the way that they have an extended rod domain (42 amino acid longer), that they all carry a nuclear localization signal (NLS) at their C-terminus and that they display typical tertiary structures. Lamin polypeptides have an almost complete α-helical conformation with multiple α-helical domains separated by non-α-helical linkers that are highly conserved in length and amino acid sequence. Both the C-terminus and the N- terminus are non α-helical, with the C-terminus displaying a globular structure. Their molecular weight ranges from 60 to 80 kilodaltons (kDa). In the amino acid sequence of nuclear lamins, there are also two phosphoacceptor sites present, flanking the central rod domain. A phosphorylation event at the onset of mitosis leads to a conformational change which causes the disassembly of the nuclear lamina. In the vertebrate genome, lamins are encoded by three genes. By alternative splicing, at least seven different polypeptides (splice variants) are obtained, some of which are specific for germ cells and play an important role in the chromatin reorganisation during meiosis. Not all organisms have the same number of lamin encoding genes; Drosophila melanogaster for example has only 2 genes, whereas Caenorhabditis elegans has only one. The presence of lamin polypeptides is an exclusive property of Metazoan organisms. Plants or single-cell Eukaryotic organisms such as Saccharomyces cerevisiae lack lamins. The nuclear lamin-associated membrane proteins are either integral or peripheral membrane proteins. The most important are lamin associated polypeptide 1 and 2 (LAP1, LAP2), emerin, lamin B-receptor (LBR), otefin and MAN1. Due to their positioning within or their association with the inner membrane, they mediate the attachment of the nuclear lamina to the nuclear envelope.[7]

Function of nuclear lamin


Chromatin organization The non-random organization of the genome strongly suggests that the nuclear lamina plays a role in chromatin organization. Indeed, it has been shown that lamin polypeptides have an affinity for binding chromatin through their α-helical (rod like) domains at specific DNA sequences called matrix attachment regions (MAR). A MAR has a length of approximately 300–1000 bp and has a high A/T content. Lamin A and B can also bind core histones through a sequence element in their tail domain.[8]



DNA replication Various experiments show that the nuclear lamina plays a part in the elongation phase of DNA replication. It has been suggested that lamins provide a scaffold, essential for the assembly of the elongation complexes, or that it provides an initiation point for the assembly of this nuclear scaffold. Not only nuclear lamina associated lamins are present during replication, but free lamin polypeptides are present as well and seem to have some regulative part in the replication process.[8]

Apoptosis Apoptosis, basically to be considered as cellular suicide is of the highest importance in homeostasis of tissue and in defending the organism against invasive entry of viruses or other pathogens. Apoptosis is a highly regulated process in which the nuclear lamina is disassembled in an early stage. In contrast to the phosphorylation-induced disassembly during mitosis, the nuclear lamina is degraded by proteolytic cleavage, and both the lamins and the nuclear lamin-associated membrane proteins are targeted. This proteolytic activity is performed by members of the caspase-protein family who cleave the lamins after aspartic acid (Asp) residues.[7][8]



In a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes. It is the second of these principles that was so original. Wilhelm Roux suggested that each chromosome carries a different genetic load. Boveri was able to test and confirm this hypothesis. Aided by the rediscovery at the start of the 1900s of Gregor Mendel's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Walter Sutton and Theophilus Painter were all influenced by Boveri (Wilson and Painter actually worked with him). In his famous textbook The Cell in Development and Heredity, Wilson linked together the independent work of Boveri and Sutton (both around 1902) by naming the chromosome theory of inheritance the "Sutton-Boveri Theory" (the names are sometimes reversed). Ernst Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T.H. Morgan, all of a rather dogmatic turn-of-mind. Eventually, complete proof came from chromosome maps in Morgan's own lab. The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes.A chromosome is an organized structure of DNA and protein that is 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. The word chromosome[9] comes from the Greek χρῶμα (chroma, colour) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes.[10]

Telomere A telomere is a region of repetitive DNA at the end of a chromosome, which protects the end of the chromosome from deterioration. Its name is derived from the Greek nouns telos "end" and merοs "part". The telomere regions deter the degradation of genes near the ends of chromosomes by allowing for the shortening of chromosome ends, which necessarily occurs during chromosome replication.

The total number of chromosomes (including sex chromosomes) present in a cell nucleus of different organisms are described below in the tables.[11]

Chromosome numbers in some plants[11]
Plant Species #[11]
Arabidopsis thaliana (diploid)[12]
Arabidopsis thaliana.jpg
Rye (diploid)[13] 14
Maize (diploid or palaeotetraploid)[14]
Stalks, ears, and silk
Einkorn wheat (diploid)[15] 14
Durum wheat (tetraploid)[15] 28
Bread wheat (hexaploid)[15]
Ears of compact wheat
Cultivated tobacco (tetraploid)[16] 48
Adder's Tongue Fern (diploid)[17]
Ophioglossum closeup.jpg
approx. 1,200
Chromosome numbers (2n) in some animals[11]
Species # Species #
Common fruit fly
Male (left) and female D. melanogaster
8 Guinea Pig[18] 64
Guppy (Poecilia reticulata)[19]
Male and female guppy.
46 Garden snail[20] 54
Earthworm (Octodrilus complanatus)[21]
Ocypus olens trying to prey on Lumbricus sp.
36 Tibetan fox 36
Domestic cat[22] 38 Domestic pig 38
Laboratory mouse[23][24]
BALB/c mice
40 Laboratory rat[24] 42
Rabbit (Oryctolagus cuniculus)[25] 44 Syrian hamster[23] 44
Hares[26][27] 48 Human[28] 46
Gorillas, Chimpanzees[28] 48 Domestic sheep 54
Elephants[29] 56 Cow 60
Donkey 62 Horse 64
Dog[30] 78 Kingfisher[31] 132
Goldfish[32] 100-104 Silkworm[33] 56
Chromosome numbers in other organisms[11]
Species Large
Trypanosoma brucei 11 6 ~100
Domestic Pigeon (Columba livia domestics)[34] 18 - 59-63
Chicken[35] 8 2 sex chromosomes 60





Splicing speckles or SC35 speckles[edit]

Sometimes referred to as interchromatin granule clusters (IGCs) or as splicing-factor compartments, speckles are rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing. Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.[36]

Cajal bodies or coiled bodies[edit]

A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies (CB), whose diameter measures between 0.2 µm and 2.0 µm depending on the cell type and species. When seen under an electron microscope, they resemble balls of tangled thread and are dense foci of distribution for the protein coilin. CBs are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.[36]

Nuclear import and export[edit]

Nuclear localization signal (NLS)[edit]

A nuclear localization signal or sequence (NLS) is an amino acid sequence which acts like a 'tag' on the exposed surface of a protein. This sequence is used to target the protein to the cell nucleus through the Nuclear Pore Complex and to direct a newly synthesized protein into the nucleus via its recognition by cytosolic nuclear transport receptors. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal, which targets proteins out of the nucleus.[37]

A. Classical NLSs Classical Nuclear localization signals can be further classified as either monopartite or bipartite. The first NLS to be discovered was the sequence PKKKRKV in the SV40 Large T-antigen (a monopartite NLS). The NLS of nucleoplasmin, KR[PAATKKAGQA]KKKK, is the prototype of the ubiquitous bipartite signal: two clusters of basic amino acids, separated by a spacer of about 10 amino acids. Both signals are recognized by importin α. Importin α contains a bipartite NLS itself, which is specifically recognized by importin β. The latter can be considered the actual import mediator. Chelsky et al. proposed the consensus sequence K-K/R-X-K/R for monopartite NLSs. A Chelsky sequence may, therefore, be part of the downstream basic cluster of a bipartite NLS. Makkerh et al. carried out comparative mutagenesis on the nuclear localisation signals of SV40 T-Antigen (monopartite), C-myc (monopartite) and nucleoplasmin (bipartite), and showed amino acid features common to all three. Notably the role of neutral and acidic amino acids was shown for the first time in contributing to the efficiency of the NLS.[37]

B. Non-classical NLSs

There are many other types of NLS, such as the acidic M9 domain of hnRNP A1, the sequence KIPIK in yeast transcription repressor Matα2, and the complex signals of U snRNPs. Most of these NLSs appear to be recognized directly by specific receptors of the importin β family without the intervention of an importin α-like protein . A signal that appears to be specific for the massively produced and transported ribosomal proteins, seems to come with a specialized set of importin β-like nuclear import receptors. Recently a class of NLSs known as PY-NLSs has been proposed, originally by Lee et al. This PY-NLS motif, so named because of the proline-tyrosine amino acid pairing in it, allows the protein to bind to Importin β2 (also known as transportin or karyopherin β2), which then translocates the cargo protein into the nucleus. The structural basis for the binding of the PY-NLS contained in Importin β2 has been determined and an inhibitor of import designed.[37]

Nuclear export signal (NES)[edit]

A nuclear export signal (NES) is a short amino acid sequence of 4 hydrophobic residues in a protein that targets it for export from the cell nucleus to the cytoplasm through the nuclear pore complex. It has the opposite effect of a nuclear localization signal, which targets a protein located in the cytoplasm for import to the nucleus. The NES is recognized and bound by exportins. In silico analysis of known NESs found the most common spacing of the hydrophobic residues to be LxxxLxxLxL, where "L" is a hydrophobic residue (often leucine) and "x" is any other amino acid; the spacing of these hydrophobic residues may be explained by examination of known structures that contain an NES, as the critical residues usually lie in the same face of adjacent secondary structures within a protein, which allows them to interact with the exportin[1]. Ribonucleic acid (RNA) are composed of nucleotides, and thus, lack the nuclear export signal to move out of the nucleus. As a result, most forms of RNA will bind to a protein molecule to form a ribonucleoprotein complex to be exported from the nucleus. Nuclear export first begins with the binding of Ran-GTP (a G-protein) to exportin. This causes a shape change in exportin, increasing its affinity for the export cargo. Once the cargo is bound, the Ran-exportin-cargo complex moves out of the nucleus through the nuclear pore. GTPase activating proteins (GAPs) then hydrolyze the Ran-GTP to Ran-GDP, and this causes a shape change and subsequent exportin release. Once no longer bound to Ran, the exportin molecule loses affinity for the nuclear cargo as well, and the complex falls apart. Exportin and Ran-GDP are recycled to the nucleus separately, and guanine exchange factor (GEF) in the nucleus switches the GDP for GTP on Ran.[37]

Role of Ran GTPase in nuclear transport during interphase[edit]

Schematic representation of the Ran cycle
Ran cycle involvement in nucleocytoplasmic transport at the nuclear pore

Ran (RAs-related Nuclear protein) is a small 25Kda protein that is involved in transport into and out of the cell nucleus during interphase and also involved in mitosis. It is a member of the Ras superfamily.Ran exists in the cell in two nucleotide-bound forms: GDP-bound and GTP-bound. RanGDP is converted into RanGTP through the action of RCC1(regulator of chromosome condensation 1), the nucleotide exchange factor for Ran. RCC1 is also known as RanGEF (Ran Guanine nucleotide Exchange Factor). Ran's intrinsic GTPase-activity is activated through interaction with Ran GTPase activating protein (RanGAP), facilitated by complex formation with Ran-binding protein (RanBP). GTPase-activation leads to the conversion of RanGTP to RanGDP, thus closing the Ran cycle.

Ran can diffuse freely within the cell, but because RCC1 and RanGAP are located in different places in the cell, the concentration of RanGTP and RanGDP differs locally as well, creating concentration gradients that act as signals for other cellular processes. RCC1 is bound to chromatin and therefore located inside the nucleus. RanGAP is cytoplasmic in yeast and bound to the nuclear envelope in plants and animals. In mammalian cells, it is SUMO modified and attached to the cytoplasmic side of the nuclear pore complex via interaction with the nucleoporin RanBP2 (Nup358). This difference in location of the accessory proteins in the Ran cycle leads to a high RanGTP to RanGDP ratio inside the nucleus and an inversely low RanGTP to RanGDP ratio outside the nucleus. In addition to a gradient of the nucleotide bound state of Ran, there is a gradient of the protein itself, with a higher concentration of Ran in the nucleus than in the cytoplasm. Cytoplasmic RanGDP is imported into the nucleus by the small protein NTF2 (Nuclear Transport Factor 2), where RCC1 can then catalyze exchange of GTP for GDP on Ran.

Ran is involved in the transport of proteins across the nuclear envelope by interacting with karyopherins and changing their ability to bind or release cargo molecules. Cargo proteins containing a nuclear localization signal (NLS) are bound by importins and transported into the nucleus. Inside the nucleus, RanGTP binds to importin and releases the import cargo. Cargo that needs to get out of the nucleus into the cytoplasm binds to exportin in a ternary complex with RanGTP. Upon hydrolysis of RanGTP to RanGDP outside the nucleus, the complex dissociates and export cargo is released.[38]


Importin also play important role in nuclear transport. Importin is a type of protein that moves other protein molecules into the nucleus by binding to a specific recognition sequence, called the nuclear localization signal (NLS). Importin is classified as a karyopherin. Importin has two subunits, importin α and importin β. Of these, importin α binds to the NLS of the protein to be imported to the nucleus whereas importin β helps in the docking of the importin heterodimer-bound protein to the nuclear pore complex. The NLS-Importin α-Importin β trimer dissociates after binding to Ran GTP inside the nucleus[39]

Function of nucleus





Facts to be remembered[edit]

Subnuclear structure sizes
Structure name Structure diameter
Cajal bodies 0.2–2.0 µm [40]
PIKA 5 µm [41]
PML bodies 0.2–1.0 µm [42]
Paraspeckles 0.2–1.0 µm
Speckles 20–25 nm [41]

Red blood cell of human doesn't contain nucleus.

Intestinal parasites in the genus Giardia which have two nuclei per cell.

Some species of protozoa and some fungi in mycorrhizaehave polynucleated cells.



The table given below lists the numbers of chromosomes in various plants, animals, protists, and other living organisms, given as the diploid number (2n)[43]

Organism Scientific name Diploid number of chromosomes Notes
African Wild Dog Lycaon pictus 78[44]
Alfalfa Medicago sativa 32[45] Cultivated alfalfa is tetraploid, with 2n=4x=32. Wild relatives have 2n=16.[45]
American Badger 32
American Marten 38
American Mink 30
Aquatic Rat Anotomys leander 92[46] Tied for highest number in mammals with Ichthyomys pittieri.
Arabidopsis thaliana 10
Barley Hordeum vulgare 14
Bat-eared Fox Otocyon megalotis 72[44]
Bean Phaseolus sp. 22[45] All species in the genus have the same chromosome number, including P. vulgaris, P. coccineus, P. acutifolis, and P. lunatus.[45]
Beaver (American) Castor canadensis 40
Beaver (Eurasian) Castor fiber 48
Beech Marten 38
Bengal Fox Vulpes bengalensis 60
Moonworts Botrychium 90
nagaho-no-nastu-no-hana-warabi Botrypus strictus 88 B. strictus and B. virginianus have been shown to be paraphyletic in the genus Botrypus
Rattlesnake fern Botrypus virginianus 184
Cabbage Brassica oleracea 18[45] Broccoli, cabbage, kale, kohlrabi, brussels sprouts, and cauliflower are all the same species and have the same chromosome number.
Carp 104
Capuchin Monkey 54[47]
Cat Felis catus 38
Chicken Gallus gallus domesticus 78
Chimpanzee Pan troglodytes 48 [48]
Chinchilla Chinchilla lanigera 64 [49]
Coatimundi 38
Cotton Gossypium hirsutum 52[45] 2n=4x; Cultivated upland cotton is derived from an allotetraploid
Cow Bos primigenius 60
Coyote Canis latrans 78[44]
Deer Mouse 48
Dhole 78
Dingo Canis lupus dingo 78[44]
Dog Canis lupus familiaris 78[50] 76 autosomal and 2 sexual.[51]
Dolphin Delphinidae Delphis 44
Donkey 62
Dove 78[52] Based on African collared dove
Fruit fly Drosophila melanogaster 8[53] 6 autosomal, and 2 sexual
Duck-billed Platypus 52
Earthworm Lumbricus terrestris 36
Echidna 63/64 63 (XXY, male) and 64 (XXXX, female)
Elephant 56
Elk (Wapiti) Cervus canadensis 68
Eurasian Badger 44
European honey bee Apis mellifera 32 32 for females, males are haploid and thus have 16.
European Mink 38
European Polecat 40
Fennec Fox Vulpes zerda 64[44]
Ferret 40
Field Horsetail 216
Fisher (animal) 38 a type of marten
Fossa 42
Giraffe Giraffa camelopardalis 62
Goat 60
Golden Jackal Canis aureus 78[44]
Gorilla 48
Gray Fox Urocyon cinereoargenteus 66[44]
Gypsy moth 62
Hawkweed 8
Hare[54][55] 48
Hedgehog Genus Atelerix (African hedgehogs) 90
Hedgehog Genus Erinaceus (Woodland hedgehogs) 88
fern-like plant Helminthostachys zeylanica 94
Horse Equus ferus caballus 64
Human Homo sapiens 46[56] 44 autosomal and 2 sex
Hyena 40
Crab-eating rat (semiaquatic rodent) Ichthyomys pittieri 92[46] highest for a mammal
Jack jumper ant Myrmecia pilosula 2[57] 2 for females, males are haploid and thus have 1; smallest number possible. Other ant species have more chromosomes.[57]
Kangaroo 12
Kit Fox 50
Lion Panthera leo 38
Long-nosed Cusimanse (a type of mongoose) 36
Maize Zea mays 20[45]
Maned Wolf Chrysocyon brachyurus 76
Mango Mangifera indica 40[45]
Meerkat 36
Mosquito Aedes aegypti 6[58] The 2n=6 chromosome number is conserved in the entire family Culicidae, except in Chagasia bathana which has 2n=8.[58]
Mouse Mus musculus 40
Mule 63 semi-infertile
Oats Avena sativa 42[45] This is a hexaploid with 2n=6x=42. Diploid and tetraploid cultivated species also exist.[45]
Adders-tongue Ophioglossum reticulatum 1200 or 1260 This fern has the highest known chromosome number.
Orangutan 48
Oriental Small-clawed Otter 38
Pea Pisum sativum 14
Pig 38
Pigeon 80
Pine Marten 38
Pineapple Ananas comosus 50[45]
Potato Solanum tuberosum 48 This is a tetraploid; wild relatives mostly have 2n=24.[45]
Porcupine Erethizon dorsatum 34 [49]
Rabbit 44
Raccoon (Procyon lotor) 38[59]
Raccoon Dog Nyctereutes viverrinus 42 some sources say sub-species differ with 38, 54, and even 56 chromosomes
Raccoon Dog Nyctereutes procyonoides 56
Radish Raphanus sativus 18
Rat 42
Red Deer Cervus elaphus 68
Red Fox Vulpes vulpes 34[44] Plus 3-5 microsomes.
Red Panda 36
Reeves's Muntjac Muntiacus reevesi 46
Rice Oryza sativa 24[45]
Rhesus Monkey 48
Rye Secale cereale 14[45]
Sable 38
Sable Antelope 46
Grape ferns Sceptridum 90
Sea Otter 38
Sheep 54
Shrimp Penaeus semisulcatus 86-92 [60]
Slime Mold Dictyostelium discoideum 12 [61]
Snail 24
Spotted Skunk 64
Starfish 36
Striped skunk 50
Swamp Wallaby Wallabia bicolor 10/11 10 for male, 11 for female
Tanuki/Raccoon Dog Nyctereutes procyonoides albus 38
Tiger Panthera tigris 38
Tibetan fox 36
Tobacco Nicotiana tabacum 48 Cultivated species is a tetraploid.[45]
Turkey 82
Virginia Opossum Didelphis virginiana 22[62]
Wheat Triticum aestivum 42[45] This is a hexaploid with 2n=6x=42. Durum wheat is Triticum turgidum var. durum, and is a tetraploid with 2n=4x=28.[45]
White-tailed deer Odocoileus virginianus 70
Wolf 78
Woolly Mammoth 58 extinct; tissue from a frozen carcass
Wolverine 42
Yellow Mongoose 36
Yeast 32
Bittersweet nightshade Solanum dulcamara 24[63][64]
Husk Tomato Physalis pubescens 24[65]

Question time[edit]

What do you know about nuclear membrane?

What is the function of nucleolus?

What is a chromosome?

Design an experiment which indicate that a particular protein is going into nucleus?

How will you determine that a particular protein X is localizing in to the nucleus not in cytoplasm?

What are importins?

What due understand with NLS?

What is the difference between active and passive transport?


  1. Cell Nucleus
  2. a b c d Cell nucleus
  3. Chi YH, Chen ZJ, Jeang KT (2009). "The nuclear envelopathies and human diseases". J. Biomed. Sci. 16: 96. doi:10.1186/1423-0127-16-96. PMID 19849840. PMC 2770040. 
  4. Nuclear envelope
  5. Nuclear envelope
  6. a b Nuclear pore
  7. a b Nuclear lamina
  8. a b c d
  10. Chromosome
  11. a b c d e f
  13. Gill BS, Kimber G (April 1974). "The Giemsa C-banded karyotype of rye". Proc. Natl. Acad. Sci. U.S.A. 71 (4): 1247–9. doi:10.1073/pnas.71.4.1247. PMID 4133848. 
  15. a b c Dubcovsky J, Luo MC, Zhong GY, et al. (1996). "Genetic map of diploid wheat, Triticum monococcum L., and its comparison with maps of Hordeum vulgare L". Genetics 143 (2): 983–99. PMID 8725244. 
  19. "The Genetics of the Popular Aquarium Pet - Guppy Fish". Retrieved 2009-12-06. 
  26. T.J. Robinson, F. Yang, W.R. Harrison (2002). "Chromosome painting refines the history of genome evolution in hares and rabbits (order Lagomorpha)". Cytogenic and Genetic Research 96 (1-4): 223–227. doi:10.1159/000063034. PMID 12438803. 
  33. Yasukochi Y, Ashakumary LA, Baba K, Yoshido A, Sahara K (2006). "A second-generation integrated map of the silkworm reveals synteny and conserved gene order between lepidopteran insects". Genetics 173 (3): 1319–28. doi:10.1534/genetics.106.055541. PMID 16547103. 
  34. Itoh, Masahiro; Tatsuro Ikeuchi, Hachiro Shimba, Michiko Mori, Motomichi Sasaki, Sajiro Makino (1969). "A COMPARATIVE KARYOTYPE STUDY IN FOURTEEN SPECIES OF BIRDS". The Japanese journal of genetics 44 (3): 163–170. doi:10.1266/jjg.44.163. ISSN 1880-5787. Retrieved 2009-10-14. 
  36. a b c
  37. a b c d Nuclear localization signal
  38. Ran (biology)
  42. Dundr, Miroslav; Tom Misteli (2001). "Functional architecture in the cell nucleus". Biochem. J. (356): 297–310. PMID 11368755. 
  43. List of organisms by chromosome count
  44. a b c d e f g h Sillero-Zubiri, Claudio; Hoffmann, Michael J.; Dave Mech (2004). Canids: Foxes, Wolves, Jackals and Dogs: Status Survey and Conservation Action Plan. World Conservation Union. ISBN 2-8317-0786-2. 
  45. a b c d e f g h i j k l m n o p q Simmonds, NW (ed.) (1976). Evolution of crop plants. New York: Longman. ISBN 0-582-44496-9. Template:Page needed
  46. a b Schmid, M.; Fernández-Badillo, A.; Feichtinger, W.; Steinlein, C.; Roman, J.I. (1988). "On the highest chromosome number in mammals". Cytogenetics and Genome Research 49 (4): 305–8. doi:10.1159/000132683. PMID 3073914. 
  47. Barnabe, Renato Campanarut; Guimarães, Marcelo Alcindo de Barros Vaz; Oliveira, CláUdio Alvarenga de; Barnabe, Alexandre Hyppolito (2002). "Analysis of some normal parameters of the spermiogram of captive capuchin monkeys (Cebus apella Linnaeus, 1758 )". Brazilian Journal of Veterinary Research and Animal Science 39. doi:10.1590/S1413-95962002000600010. 
  48. Young WJ, Merz T, Ferguson-Smith MA, Johnston AW (June 1960). "Chromosome number of the chimpanzee, Pan troglodytes". Science 131: 1672–3. doi:10.1126/science.131.3414.1672. PMID 13846659. 
  49. a b
  52. Guttenbach M, Nanda I, Feichtinger W, Masabanda JS, Griffin DK, Schmid M (2003). "Comparative chromosome painting of chicken autosomal paints 1-9 in nine different bird species". Cytogenetics and Genome Research 103 (1-2): 173–84. doi:10.1159/000076309. PMID 15004483. 
  53. "Drosophila Genome Project". National Center for Biotechnology Information. Retrieved 2009-04-14. 
  54. T.J. Robinson, F. Yang, W.R. Harrison (2002). "Chromosome painting refines the history of genome evolution in hares and rabbits (order Lagomorpha)". Cytogenics and Genetic Research 96: 223–227. doi:10.1159/000063034. PMID 12438803. 
  56. "Human Genome Project". National Center for Biotechnology Information. Retrieved 2009-04-29. 
  57. a b Crosland, M.W.J., Crozier, R.H. (1986). "Myrmecia pilosula, an ant with only one pair of chromosomes". Science 231 (4743): 1278. doi:10.1126/science.231.4743.1278. PMID 17839565. 
  58. a b Francesco Giannelli; Hall, Jeffrey C.; Dunlap, Jay C.; Friedmann, Theodore (1999). Advances in Genetics, Volume 41 (Advances in Genetics). Boston: Academic Press. p. 2. ISBN 0-12-017641-6. 
  59. Perelman PL, Graphodatsky AS, Dragoo JW, Serdyukova NA, Stone G, Cavagna P, Menotti A, Nie W, O'Brien PC, Wang J, Burkett S, Yuki K, Roelke ME, O'Brien SJ, Yang F, Stanyon R (2008). "Chromosome painting shows that skunks (Mephitidae, Carnivora) have highly rearranged karyotypes". Chromosome Res. 16 (8): 1215–31. doi:10.1007/s10577-008-1270-2. PMID 19051045. 
  60. Hosseini S-J, Elahi E, Raie RM (2004). "The Chromosome Number of the Persian Gulf Shrimp Penaeus semisulcatus". Iranian Int. J. Sci 5 (1): 13–23. 
  61. "First of six chromosomes sequenced in Dictyostelium discoideum". Genome News Network. Retrieved 2009-04-29. 
  62. Biggers JD, Fritz HI, Hare WC, McFeely RA (June 1965). "Chromosomes of American Marsupials". Science 148: 1602–3. doi:10.1126/science.148.3677.1602. PMID 14287602. 
  63. Abrams, L. (1951). Illustrated Flora of the Pacific States. Volume 3.. Stanford University Press. pp. 866. 
  64. Stance, C. (1997). New Flora of the British Isles. Second Edition.. Cambridge, UK. pp. 1130. 
  65. Liang, X; Bing, W. (April 2004). "[Karyotype analysis of Physalis pubescens chromosome](article in Chinese)". Zhong Yao Cai. 27 (4): 238–239.