Cell (biology) 1

Cell (biology)

Allium cells in different phases of the cell cycle

The cells of eukaryotes (left) and prokaryotes (right)

The cell is the basic structural andfunctional unit of all known livingorganisms. It is the smallest unit of lifethat is classified as a living thing, andis often called the building block oflife.[1] Organisms can be classified asunicellular (consisting of a single cell;including most bacteria) ormulticellular (including plants andanimals). Humans contain about 10trillion (1013) cells. Most plant andanimal cells are between 1 and 100 µmand therefore are visible only under themicroscope.[2]

The cell was discovered by RobertHooke in 1665. The cell theory, firstdeveloped in 1839 by Matthias JakobSchleiden and Theodor Schwann,states that all organisms are composedof one or more cells, that all cells comefrom preexisting cells, that vitalfunctions of an organism occur withincells, and that all cells contain thehereditary information necessary forregulating cell functions and fortransmitting information to the nextgeneration of cells.[3]

The word cell comes from the Latin cella, meaning "small room". The descriptive term for the smallest livingbiological structure was coined by Robert Hooke in a book he published in 1665 when he compared the cork cells hesaw through his microscope to the small rooms monks lived in.[4]

AnatomyThere are two types of cells: eukaryotic and prokaryotic. Prokaryotic cells are usually independent, while eukaryoticcells are often found in multicellular organisms.

Cell (biology) 2

Table 1: Comparison of features of prokaryotic and eukaryotic cells

Prokaryotes Eukaryotes

Typical organisms bacteria, archaea protists, fungi, plants, animals

Typical size ~ 1–10 µm ~ 10–100 µm (sperm cells, apart from the tail, are smaller)

Type of nucleus nucleoid region; no real nucleus real nucleus with double membrane

DNA circular (usually) linear molecules (chromosomes) with histone proteins

RNA-/protein-synthesis coupled in cytoplasm RNA-synthesis inside the nucleusprotein synthesis in cytoplasm

Ribosomes 50S+30S 60S+40S

Cytoplasmatic structure very few structures highly structured by endomembranes and a cytoskeleton

Cell movement flagella made of flagellin flagella and cilia containing microtubules; lamellipodia and filopodia containing actin

Mitochondria none one to several thousand (though some lack mitochondria)

Chloroplasts none in algae and plants

Organization usually single cells single cells, colonies, higher multicellular organisms with specialized cells

Cell division Binary fission (simple division) Mitosis (fission or budding)Meiosis

Prokaryotic cells

Diagram of a typical prokaryotic cell

The prokaryote cell is simpler, andtherefore smaller, than a eukaryotecell, lacking a nucleus and most of theother organelles of eukaryotes. Thereare two kinds of prokaryotes: bacteriaand archaea; these share a similarstructure.

The nuclear material of a prokaryoticcell consists of a single chromosomethat is in direct contact with thecytoplasm. Here, the undefined nuclearregion in the cytoplasm is called thenucleoid.

A prokaryotic cell has threearchitectural regions:• On the outside, flagella and pili

project from the cell's surface.These are structures (not present inall prokaryotes) made of proteins that facilitate movement and communication between cells;

• Enclosing the cell is the cell envelope – generally consisting of a cell wall covering a plasma membrane thoughsome bacteria also have a further covering layer called a capsule. The envelope gives rigidity to the cell andseparates the interior of the cell from its environment, serving as a protective filter. Though most prokaryoteshave a cell wall, there are exceptions such as Mycoplasma (bacteria) and Thermoplasma (archaea). The cell wall

Cell (biology) 3

consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents thecell from expanding and finally bursting (cytolysis) from osmotic pressure against a hypotonic environment.Some eukaryote cells (plant cells and fungal cells) also have a cell wall;

• Inside the cell is the cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts ofinclusions. A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacteriumBorrelia burgdorferi, which causes Lyme disease).[5] Though not forming a nucleus, the DNA is condensed in anucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular.Plasmids enable additional functions, such as antibiotic resistance.

Eukaryotic cellsPlants, animals, fungi, slime moulds, protozoa, and algae are all eukaryotic. These cells are about 15 times widerthan a typical prokaryote and can be as much as 1000 times greater in volume. The major difference betweenprokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specificmetabolic activities take place. Most important among these is a cell nucleus, a membrane-delineated compartmentthat houses the eukaryotic cell's DNA. This nucleus gives the eukaryote its name, which means "true nucleus." Otherdifferences include:•• The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls

may or may not be present.• The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated

with histone proteins. All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by amembrane. Some eukaryotic organelles such as mitochondria also contain some DNA.

• Many eukaryotic cells are ciliated with primary cilia. Primary cilia play important roles in chemosensation,mechanosensation, and thermosensation. Cilia may thus be "viewed as sensory cellular antennae that coordinate alarge number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternativelyto cell division and differentiation."[6]

• Eukaryotes can move using motile cilia or flagella. The flagella are more complex than those of prokaryotes.

Structure of a typical animal cell Structure of a typical plant cell

Cell (biology) 4

Table 2: Comparison of structures between animal and plant cells

Typical animal cell Typical plant cell

Organelles •• Nucleus

• Nucleolus (within nucleus)• Rough endoplasmic reticulum (ER)•• Smooth ER• Ribosomes•• Cytoskeleton•• Golgi apparatus•• Cytoplasm•• Mitochondria•• Vesicles• Lysosomes•• Centrosome

• Centrioles

•• Nucleus

• Nucleolus (within nucleus)•• Rough ER•• Smooth ER•• Ribosomes•• Cytoskeleton• Golgi apparatus (dictiosomes)•• Cytoplasm•• Mitochondria• Plastids and its derivatives• Vacuole(s)•• Cell wall

Subcellular componentsAll cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, separates its interior from itsenvironment, regulates what moves in and out (selectively permeable), and maintains the electric potential of thecell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditarymaterial of genes, and RNA, containing the information necessary to build various proteins such as enzymes, thecell's primary machinery. There are also other kinds of biomolecules in cells. This article lists these primarycomponents of the cell, then briefly describe their function.

MembraneThe cytoplasm of a cell is surrounded by a cell membrane or plasma membrane. The plasma membrane in plants andprokaryotes is usually covered by a cell wall. This membrane serves to separate and protect a cell from itssurrounding environment and is made mostly from a double layer of lipids (hydrophobic fat-like molecules) andhydrophilic phosphorus molecules. Hence, the layer is called a phospholipid bilayer. It may also be called a fluidmosaic membrane. Embedded within this membrane is a variety of protein molecules that act as channels and pumpsthat move different molecules into and out of the cell. The membrane is said to be 'semi-permeable', in that it caneither let a substance (molecule or ion) pass through freely, pass through to a limited extent or not pass through at all.Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such ashormones.

Cell (biology) 5

Cytoskeleton

Bovine Pulmonary Artery Endothelial cell: nuclei stained blue,mitochondria stained red, and F-actin, an important component in

microfilaments, stained green. Cell imaged on a fluorescentmicroscope.

The cytoskeleton acts to organize and maintain thecell's shape; anchors organelles in place; helps duringendocytosis, the uptake of external materials by a cell,and cytokinesis, the separation of daughter cells aftercell division; and moves parts of the cell in processes ofgrowth and mobility. The eukaryotic cytoskeleton iscomposed of microfilaments, intermediate filamentsand microtubules. There is a great number of proteinsassociated with them, each controlling a cell's structureby directing, bundling, and aligning filaments. Theprokaryotic cytoskeleton is less well-studied but isinvolved in the maintenance of cell shape, polarity andcytokinesis.[7]

Genetic material

Two different kinds of genetic material exist:deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term informationstorage, but some viruses (e.g., retroviruses) have RNA as their genetic material. The biological informationcontained in an organism is encoded in its DNA or RNA sequence. RNA is also used for information transport (e.g.,mRNA) and enzymatic functions (e.g., ribosomal RNA) in organisms that use DNA for the genetic code itself.Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in thenucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules calledchromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondriaand chloroplasts (see endosymbiotic theory).A human cell has genetic material contained in the cell nucleus (the nuclear genome) and in the mitochondria (themitochondrial genome). In humans the nuclear genome is divided into 23 pairs of linear DNA molecules calledchromosomes. The mitochondrial genome is a circular DNA molecule distinct from the nuclear DNA. Although themitochondrial DNA is very small compared to nuclear chromosomes, it codes for 13 proteins involved inmitochondrial energy production and specific tRNAs.Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process calledtransfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is. Certain virusesalso insert their genetic material into the genome.

OrganellesThe human body contains many different organs, such as the heart, lung, and kidney, with each organ performing adifferent function. Cells also have a set of "little organs," called organelles, that are adapted and/or specialized forcarrying out one or more vital functions. Both eukaryotic and prokaryotic cells have organelles but organelles ineukaryotes are generally more complex and may be membrane bound.There are several types of organelles in a cell. Some (such as the nucleus and golgi apparatus) are typically solitary,while others (such as mitochondria, peroxisomes and lysosomes) can be numerous (hundreds to thousands). Thecytosol is the gelatinous fluid that fills the cell and surrounds the organelles.

Cell (biology) 6

Diagram of a cell nucleus

• Cell nucleus – eukaryotes only - A cell's information center, thecell nucleus is the most conspicuous organelle found in a eukaryoticcell. It houses the cell's chromosomes, and is the place where almostall DNA replication and RNA synthesis (transcription) occur. Thenucleus is spherical and separated from the cytoplasm by a doublemembrane called the nuclear envelope. The nuclear envelopeisolates and protects a cell's DNA from various molecules that couldaccidentally damage its structure or interfere with its processing.During processing, DNA is transcribed, or copied into a specialRNA, called messenger RNA (mRNA). This mRNA is thentransported out of the nucleus, where it is translated into a specificprotein molecule. The nucleolus is a specialized region within thenucleus where ribosome subunits are assembled. In prokaryotes,DNA processing takes place in the cytoplasm.

• Mitochondria and Chloroplasts – eukaryotes only - the power generators: Mitochondria are self-replicatingorganelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondriaplay a critical role in generating energy in the eukaryotic cell. Mitochondria generate the cell's energy byoxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining toglucose) to generate ATP. Mitochondria multiply by splitting in two. Respiration occurs in the cell mitochondria.

Diagram of an endomembrane system

• Endoplasmic reticulum – eukaryotes only: The endoplasmicreticulum (ER) is the transport network for molecules targeted forcertain modifications and specific destinations, as compared tomolecules that float freely in the cytoplasm. The ER has two forms:the rough ER, which has ribosomes on its surface and secretesproteins into the cytoplasm, and the smooth ER, which lacks them.Smooth ER plays a role in calcium sequestration and release.

• Golgi apparatus – eukaryotes only : The primary function of theGolgi apparatus is to process and package the macromolecules suchas proteins and lipids that are synthesized by the cell.

• Ribosomes: The ribosome is a large complex of RNA and proteinmolecules. They each consist of two subunits, and act as anassembly line where RNA from the nucleus is used to synthesiseproteins from amino acids. Ribosomes can be found either floatingfreely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane inprokaryotes).[8]

• Lysosomes and Peroxisomes – eukaryotes only: Lysosomes contain digestive enzymes (acid hydrolases). Theydigest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Peroxisomes have enzymesthat rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not containedin a membrane-bound system.

• Centrosome – the cytoskeleton organiser: The centrosome produces the microtubules of a cell – a keycomponent of the cytoskeleton. It directs the transport through the ER and the Golgi apparatus. Centrosomes arecomposed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle.A single centrosome is present in the animal cells. They are also found in some fungi and algae cells.

• Vacuoles: Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane. Some cells, most notably Amoeba, have contractile vacuoles,

Cell (biology) 7

which can pump water out of the cell if there is too much water. The vacuoles of eukaryotic cells are usuallylarger in those of plants than animals.

Structures outside the cell membraneMany cells also have structures which exist wholly or partially outside the cell membrane. These structures arenotable because they are not protected from the external environment by the impermeable cell membrane. In order toassemble these structures export processes to carry macromolecules across the cell membrane must be used.

Cell wallMany types of prokaryotic and eukaryotic cell have a cell wall. The cell wall acts to protect the cell mechanicallyand chemically from its environment, and is an additional layer of protection to the cell membrane. Different typesof cell have cell walls made up of different materials; plant cell walls are primarily made up of pectin, fungi cellwalls are made up of chitin and bacteria cell walls are made up of peptidoglycan.

Prokaryotic

Capsule

A gelatinous capsule is present in some bacteria outside the cell membrane and cell wall. The capsule may bepolysaccharide as in pneumococci, meningococci or polypeptide as Bacillus anthracis or hyaluronic acid as instreptococci. Capsules are not marked by normal staining protocols and can be detected by special stain.

Flagella

Flagella are organelles for cellular mobility. The bacterial flagellum stretches from cytoplasm through the cellmembrane(s) and extrudes through the cell wall. They are long and thick thread-like appendages, protein in nature.Are most commonly found in bacteria cells but are found in animal cells as well.

Fimbriae (pili)

They are short and thin hair like filaments, formed of protein called pilin (antigenic). Fimbriae are responsible forattachment of bacteria to specific receptors of human cell (adherence). There are special types of pili called (sex pili)involved in conjunction.

Functions

Growth and metabolismBetween successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is theprocess by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, inwhich the cell breaks down complex molecules to produce energy and reducing power, and anabolism, in which thecell uses energy and reducing power to construct complex molecules and perform other biological functions.Complex sugars consumed by the organism can be broken down into a less chemically complex sugar moleculecalled glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form ofenergy, through two different pathways.The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction isdesigned to produce some hydrogen ions that can then be used to make energy packets (ATP). In prokaryotes,glycolysis is the only method used for converting energy.The second pathway, called the Krebs cycle, or citric acid cycle, occurs inside the mitochondria and can generateenough ATP to run all the cell functions.

Cell (biology) 8

An overview of proteinsynthesis.Within the

nucleus of the cell (lightblue), genes (DNA, darkblue) are transcribed intoRNA. This RNA is then

subject topost-transcriptional

modification and control,resulting in a mature

mRNA (red) that is thentransported out of thenucleus and into the

cytoplasm (peach), whereit undergoes translationinto a protein. mRNA istranslated by ribosomes(purple) that match the

three-base codons of themRNA to the three-base

anti-codons of theappropriate tRNA. Newly

synthesized proteins(black) are often further

modified, such as bybinding to an effectormolecule (orange), tobecome fully active.

Creation

Cell division involves a single cell (called a mother cell) dividing into two daughtercells. This leads to growth in multicellular organisms (the growth of tissue) and toprocreation (vegetative reproduction) in unicellular organisms.

Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process ofnuclear division, called mitosis, followed by division of the cell, called cytokinesis. Adiploid cell may also undergo meiosis to produce haploid cells, usually four. Haploidcells serve as gametes in multicellular organisms, fusing to form new diploid cells.

DNA replication, or the process of duplicating a cell's genome, is required every time acell divides. Replication, like all cellular activities, requires specialized proteins forcarrying out the job.

Protein synthesis

Cells are capable of synthesizing new proteins, which are essential for the modulationand maintenance of cellular activities. This process involves the formation of newprotein molecules from amino acid building blocks based on information encoded inDNA/RNA. Protein synthesis generally consists of two major steps: transcription andtranslation.

Transcription is the process where genetic information in DNA is used to produce acomplementary RNA strand. This RNA strand is then processed to give messenger RNA(mRNA), which is free to migrate through the cell. mRNA molecules bind toprotein-RNA complexes called ribosomes located in the cytosol, where they aretranslated into polypeptide sequences. The ribosome mediates the formation of apolypeptide sequence based on the mRNA sequence. The mRNA sequence directlyrelates to the polypeptide sequence by binding to transfer RNA (tRNA) adaptermolecules in binding pockets within the ribosome. The new polypeptide then folds into afunctional three-dimensional protein molecule.

Movement or motility

Cells can move during many processes: such as wound healing, the immune responseand cancer metastasis. For wound healing to occur, white blood cells and cells that ingestbacteria move to the wound site to kill the microorganisms that cause infection.At the same time fibroblasts (connective tissue cells) move there to remodel damaged structures. In the case of tumordevelopment, cells from a primary tumor move away and spread to other parts of the body. Cell motility involvesmany receptors, crosslinking, bundling, binding, adhesion, motor and other proteins.[9] The process is divided intothree steps – protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell bodyand rear, and cytoskeletal contraction to pull the cell forward. Each step is driven by physical forces generated byunique segments of the cytoskeleton.[10][11]

Cell (biology) 9

OriginsThe origin of cells has to do with the origin of life, which began the history of life on Earth.

Origin of the first cellThere are several theories about the origin of small molecules that could lead to life in an early Earth. One is thatthey came from meteorites (see Murchison meteorite). Another is that they were created at deep-sea vents. A third isthat they were synthesized by lightning in a reducing atmosphere (see Miller–Urey experiment); although it is notclear if Earth had such an atmosphere. There are essentially no experimental data defining what the firstself-replicating forms were. RNA is generally assumed the earliest self-replicating molecule, as it is capable of bothstoring genetic information and catalyzing chemical reactions (see RNA world hypothesis). But some other entitywith the potential to self-replicate could have preceded RNA, like clay or peptide nucleic acid.[12]

Cells emerged at least 4.0–4.3 billion years ago. The current belief is that these cells were heterotrophs. Animportant characteristic of cells is the cell membrane, composed of a bilayer of lipids. The early cell membraneswere probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid. Lipids areknown to spontaneously form bilayered vesicles in water, and could have preceded RNA, but the first cellmembranes could also have been produced by catalytic RNA, or even have required structural proteins before theycould form.[13]

Origin of eukaryotic cellsThe eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearingorganelles like the mitochondria and the chloroplasts are almost certainly what remains of ancient symbioticoxygen-breathing proteobacteria and cyanobacteria, respectively, where the rest of the cell appears derived from anancestral archaean prokaryote cell—an idea called the endosymbiotic theory.There is still considerable debate about whether organelles like the hydrogenosome predated the origin ofmitochondria, or viceversa: see the hydrogen hypothesis for the origin of eukaryotic cells.Sex, as the stereotyped choreography of meiosis and syngamy that persists in nearly all extant eukaryotes, may haveplayed a role in the transition from prokaryotes to eukaryotes. An 'origin of sex as vaccination' theory suggests thatthe eukaryote genome accreted from prokaryan parasite genomes in numerous rounds of lateral gene transfer.Sex-as-syngamy (fusion sex) arose when infected hosts began swapping nuclearized genomes containing co-evolved,vertically transmitted symbionts that conveyed protection against horizontal infection by more virulentsymbionts.[14]

History of research• 1632–1723: Antonie van Leeuwenhoek teaches himself to grind lenses, builds a microscope and draws protozoa,

such as Vorticella from rain water, and bacteria from his own mouth.• 1665: Robert Hooke discovers cells in cork, then in living plant tissue using an early microscope.[4]

• 1839: Theodor Schwann and Matthias Jakob Schleiden elucidate the principle that plants and animals are made ofcells, concluding that cells are a common unit of structure and development, and thus founding the cell theory.

• The belief that life forms can occur spontaneously (generatio spontanea) is contradicted by Louis Pasteur(1822–1895) (although Francesco Redi had performed an experiment in 1668 that suggested the sameconclusion).

• 1855: Rudolf Virchow states that cells always emerge from cell divisions (omnis cellula ex cellula).• 1931: Ernst Ruska builds first transmission electron microscope (TEM) at the University of Berlin. By 1935, he

has built an EM with twice the resolution of a light microscope, revealing previously unresolvable organelles.• 1953: Watson and Crick made their first announcement on the double-helix structure for DNA on February 28.

Cell (biology) 10

• 1981: Lynn Margulis published Symbiosis in Cell Evolution detailing the endosymbiotic theory.

References[1] Cell Movements and the Shaping of the Vertebrate Body (http:/ / www. ncbi. nlm. nih. gov/ entrez/ query. fcgi?cmd=Search& db=books&

doptcmdl=GenBookHL& term=Cell+ Movements+ and+ the+ Shaping+ of+ the+ Vertebrate+ Body+ AND+ mboc4[book]+ AND+374635[uid]& rid=mboc4. section. 3919) in Chapter 21 of Molecular Biology of the Cell (http:/ / www. ncbi. nlm. nih. gov/ entrez/ query.fcgi?cmd=Search& db=books& doptcmdl=GenBookHL& term=cell+ biology+ AND+ mboc4[book]+ AND+ 373693[uid]& rid=mboc4)fourth edition, edited by Bruce Alberts (2002) published by Garland Science.The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe smallmolecules such as amino acids as " molecular building blocks (http:/ / www. ncbi. nlm. nih. gov/ entrez/ query. fcgi?cmd=Search&db=books& doptcmdl=GenBookHL& term="all+ cells"+ AND+ mboc4[book]+ AND+ 372023[uid]& rid=mboc4. section. 4#23)".

[2] Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life (http:/ / www. phschool. com/ el_marketing. html).Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. .

[3] Maton, Anthea; Hopkins, Jean Johnson, Susan LaHart, David Quon Warner, Maryanna Wright, Jill D (1997). Cells Building Blocks of Life.New Jersey: Prentice Hall. ISBN 0-13-423476-6.

[4] "... I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular[..] these pores, or cells, [..] were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with anyWriter or Person, that had made any mention of them before this. . ." – Hooke describing his observations on a thin slice of cork. RobertHooke (http:/ / www. ucmp. berkeley. edu/ history/ hooke. html)

[5] European Bioinformatics Institute, Karyn's Genomes: Borrelia burgdorferi (http:/ / www. ebi. ac. uk/ 2can/ genomes/ bacteria/Borrelia_burgdorferi. html), part of 2can on the EBI-EMBL database. Retrieved 5 August 2012

[6] Satir, P; Christensen, ST; Søren T. Christensen (2008-03-26). "Structure and function of mammalian cilia" (http:/ / www. springerlink. com/content/ x5051hq648t3152q/ ). Histochemistry and Cell Biology (Springer Berlin / Heidelberg) 129 (6): 687–693.doi:10.1007/s00418-008-0416-9. PMC 2386530. PMID 18365235. 1432-119X. . Retrieved 2009-09-12.

[7] Michie K, Löwe J (2006). "Dynamic filaments of the bacterial cytoskeleton". Annu Rev Biochem 75: 467–92.doi:10.1146/annurev.biochem.75.103004.142452. PMID 16756499.

[8] Ménétret JF, Schaletzky J, Clemons WM, et al., CW; Akey (December 2007). "Ribosome binding of a single copy of the SecY complex:implications for protein translocation". Mol. Cell 28 (6): 1083–92. doi:10.1016/j.molcel.2007.10.034. PMID 18158904.

[9] Revathi Ananthakrishnan1 *, Allen Ehrlicher2 ✉. "The Forces Behind Cell Movement" (http:/ / www. biolsci. org/ v03p0303. htm).Biolsci.org. . Retrieved 2009-04-17.

[10][10] Alberts B, Johnson A, Lewis J. et al. Molecular Biology of the Cell, 4e. Garland Science. 2002[11] Ananthakrishnan R, Ehrlicher A. The Forces Behind Cell Movement. Int J Biol Sci 2007; 3:303–317. http:/ / www. biolsci. org/ v03p0303.

htm[12] Orgel LE (1998). "The origin of life--a review of facts and speculations". Trends Biochem Sci 23 (12): 491–5.

doi:10.1016/S0968-0004(98)01300-0. PMID 9868373.[13] Griffiths G (December 2007). "Cell evolution and the problem of membrane topology". Nature reviews. Molecular cell biology 8 (12):

1018–24. doi:10.1038/nrm2287. PMID 17971839.[14] Sterrer W (2002). "On the origin of sex as vaccination". Journal of Theoretical Biology 216: 387–396. doi:10.1006/jtbi.2002.3008.

PMID 12151256.

•  This article incorporates public domain material from the NCBI document "Science Primer" (http:/ / www.ncbi. nlm. nih. gov/ About/ primer/ index. html).

External links• Inside the Cell (http:/ / publications. nigms. nih. gov/ insidethecell/ )• Virtual Cell's Educational Animations (http:/ / vcell. ndsu. nodak. edu/ animations/ )• The Inner Life of A Cell (http:/ / www. studiodaily. com/ main/ searchlist/ 6850. html), a flash video showing

what happens inside of a cell. Daniel Reda of Singularity University narrates (beginning at 22:24) (http:/ / www.youtube. com/ watch?v=It83JKAxejM)

• The Virtual Cell (http:/ / www. ibiblio. org/ virtualcell/ tour/ cell/ cell. htm)• Cells Alive! (http:/ / www. cellsalive. com/ )• Journal of Cell Biology (http:/ / www. jcb. org/ )• The Biology Project > Cell Biology (http:/ / www. biology. arizona. edu/ cell_bio/ cell_bio. html)• Centre of the Cell online (http:/ / www. centreofthecell. org/ )

Cell (biology) 11

• The Image & Video Library of The American Society for Cell Biology (http:/ / cellimages. ascb. org/ ), acollection of peer-reviewed still images, video clips and digital books that illustrate the structure, function andbiology of the cell.

• HighMag Blog (http:/ / highmagblog. blogspot. com/ ), still images of cells from recent research articles.• New Microscope Produces Dazzling 3D Movies of Live Cells (http:/ / www. hhmi. org/ news/ betzig20110304.

html), March 4, 2011 - Howard Hughes Medical Institute.• WormWeb.org: Interactive Visualization of the C. elegans Cell lineage (http:/ / wormweb. org/ celllineage) -

Visualize the entire cell lineage tree of the nematode C. elegans

Textbooks• Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). Molecular Biology of the Cell (http:/ / www.

ncbi. nlm. nih. gov/ books/ bv. fcgi?rid=mboc4. TOC& depth=2) (4th ed.). Garland. ISBN 0-8153-3218-1.• Lodish H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipurksy SL, Darnell J (2004). Molecular

Cell Biology (http:/ / www. ncbi. nlm. nih. gov/ books/ bv. fcgi?rid=mcb. TOC) (5th ed.). WH Freeman: NewYork, NY. ISBN 978-0-7167-4366-8.

• Cooper GM (2000). The cell: a molecular approach (http:/ / www. ncbi. nlm. nih. gov/ books/ bv.fcgi?rid=cooper. TOC& depth=2) (2nd ed.). Washington, D.C: ASM Press. ISBN 0-87893-102-3.

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Article Sources and ContributorsCell (biology)  Source: http://en.wikipedia.org/w/index.php?oldid=508225079  Contributors: .:Ajvol:., 041744, 168..., 1pezguy, 1tinyboo, 2004-12-29T22:45Z, 209.234.79.xxx, 2D, 2help,2over0, 83d40m, A3RO, A8UDI, A:f6, AOB, Abbypettis, Abdullais4u, Acalamari, Acather96, Accurizer, Ace of Spades, Acer al2017, Acroterion, Adam.J.W.C., Adam78, AdamRetchless,Adamstevenson, Adapter, Adenosine, AdjustShift, Aeonx, Afctenfour, Ahoerstemeier, Ajh16, Ajraddatz, Akanemoto, Akradecki, Alan Liefting, Alansohn, Ale jrb, AlexiusHoratius,Alisonthegreat, Alvarogonzalezsotillo, Alxeedo, Amren, AnakngAraw, Anclation, Andonic, Andre Engels, Andrea105, Andres, Andrew4010, Andy120290, Andycjp, Animum, Anna Lincoln,Anonymous Dissident, Anphanax, Antandrus, Anthere, Arc de Ciel, Arcadian, ArglebargleIV, Arjun01, Art LaPella, Arti Sahajpal, Ascidian, Aua, AuburnPilot, Average Earthman, Avicennasis,Avono, Avs5221, AxelBoldt, Backslash Forwardslash, Bart133, Bbasen, Bcorr, 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Image Sources, Licenses and ContributorsFile:Wilson1900Fig2.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wilson1900Fig2.jpg  License: Public Domain  Contributors: Edmund Beecher WilsonImage:celltypes.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Celltypes.svg  License: Public Domain  Contributors: Science Primer (National Center for BiotechnologyInformation). Vectorized by Mortadelo2005.Image:Average prokaryote cell- en.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Average_prokaryote_cell-_en.svg  License: Public Domain  Contributors: Mariana RuizVillarreal, LadyofHatsImage:Animal cell structure en.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Animal_cell_structure_en.svg  License: Public Domain  Contributors: LadyofHats (Mariana Ruiz)Image:Plant cell structure svg.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Plant_cell_structure_svg.svg  License: Public Domain  Contributors: LadyofHats (Mariana Ruiz)File:DAPIMitoTrackerRedAlexaFluor488BPAE.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:DAPIMitoTrackerRedAlexaFluor488BPAE.jpg  License: Creative CommonsAttribution-Sharealike 3.0  Contributors: IP69.226.103.13Image:Diagram human cell nucleus no text.png  Source: http://en.wikipedia.org/w/index.php?title=File:Diagram_human_cell_nucleus_no_text.png  License: Public Domain  Contributors:Mariana Ruiz Villarreal LadyofHats. Original uploader was Peter Znamenskiy at en.wikipediaImage:Endomembrane system diagram no text nucleus.png  Source: http://en.wikipedia.org/w/index.php?title=File:Endomembrane_system_diagram_no_text_nucleus.png  License: Publicdomain  Contributors: Peter Znamenskiy at en.wikipediaImage:Proteinsynthesis.png  Source: http://en.wikipedia.org/w/index.php?title=File:Proteinsynthesis.png  License: Public Domain  Contributors: Incnis Mrsi, Laikayiu, 1 anonymous editsImage:PD-icon.svg  Source: http://en.wikipedia.org/w/index.php?title=File:PD-icon.svg  License: Public Domain  Contributors: Alex.muller, Anomie, Anonymous Dissident, CBM, MBisanz,PBS, Quadell, Rocket000, Strangerer, Timotheus Canens, 1 anonymous edits

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