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Reed-Sternberg Cell

Reed-Sternberg cell

Reed-Sternberg cells are abnormal cells found on light microscopy in biopsies from individuals with Hodgkin's disease (a type of lymphoma), and certain other disorders. They are derived from B lymphocytes. They are named after Dorothy Reed (1874-1964) and either Carl von Sternberg or George M. Sternberg (1838-1915) - there is conflicting data on which is the correct Sternberg. Reed-Sternberg cells are large and are either multinucleated or have a bilobed nucleus (thus resembling an "owl's eye" appearance) with prominent eosinophilic inclusion-like nucleoli. Reed-Sternberg cells are CD30 and CD15 positive. Although the presence of these cells is necessary for the diagnosis of Hodgkin's lymphoma (where the number of cells found in the lesion is directly proportional to the severity of the disease variants), cells are found in other disorders as well (such as infectious mononucleosis).

External links


- [http://www-medlib.med.utah.edu/WebPath/HEMEHTML/HEME045.html Image]
- [http://www.bioltrop.org/09-diagautre/reed-sternberg-fort.jpg Image]
- [http://www.thecrookstoncollection.com/Collection/medslides/Slides/Reed-Sternberg-cell.jpg Image] Category:Anatomical pathology Category:Eponymous anatomical structures

Cell (biology)

(red) and DNA (green)]] The cell is the structural and functional unit of all living organisms, and are sometimes called the "building blocks of life." Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, (humans have an estimated 100,000 billion or 1014 cells). The cell theory, first developed in 1839 by Schleiden and Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells and that cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells. The word cell comes from the Latin cella, a small room. The name was chosen by Robert Hooke when he compared the cork cells he saw to small rooms monks lived in.

Overview

Properties of cells

cork Each cell is at least somewhat self-contained and self-maintaining: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Each cell stores its own set of instructions for carrying out each of these activities. All cells share several abilities:
- Reproduction by cell division.
- Metabolism, including taking in raw materials, building cell components, creating energy, molecules and releasing by-products. The functioning of a cell depends upon its ability to extract and use chemical energy stored in organic molecules. This energy is derived from metabolic pathways.
- Synthesis of proteins, the functional workhorses of cells, such as enzymes. A typical mammalian cell contains up to 10,000 different proteins.
- Response to external and internal stimuli such as changes in temperature, pH or nutrient levels.
- Traffic of vesicles.

Types of cells

vesicle One way to classify cells is whether they live alone or in groups. Organisms vary from single cells (called single-celled or unicellular organisms) that function and survive more or less independently, through colonial forms with cells living together, to multicellular forms in which cells are specialized. 220 types of cells and tissues make up the multicellular human body. Cells can also be classified into two categories based on their internal structure.
- Prokaryotic cells are structurally simple. They are found only in single-celled and colonial organisms. In the three-domain system of scientific classification, prokaryotic cells are placed in the domains Archaea and Eubacteria.
- Eukaryotic cells have organelles with their own membranes. Single-celled eukaryotic organisms such as amoebae and some fungi are very diverse, but many colonial and multicellular forms such as plants, animals, and brown algae also exist.

Subcellular components

brown alga (2) nucleus (3) ribosome (4) vesicle,(5) rough endoplasmic reticulum (ER), (6) Golgi apparatus, (7) Cytoskeleton, (8) smooth ER, (9) mitochondria, (10) vacuole, (11) cytoplasm, (12) lysosome, (13) centrioles]] centriole All cells whether prokaryotic or eukaryotic have a membrane, which envelopes the cell, separates its interior from its environment, controls what moves in and out, and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes and RNA, which contain the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells. This article will list these primary components of the cell then briefly describe their function.

Cell membrane - a cell's protective coat

Main article: Cell membrane The cytoplasm of a eukaryotic cell is surrounded by a plasma membrane. A form of plasma membrane is also found in prokaryotes, but is usually referred to as the cell membrane. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of lipids (fat-like molecules) and proteins. Embedded within this membrane are a variety of other molecules that act as channels and pumps, moving different molecules into and out of the cell.

Cytoskeleton - a cell's scaffold

Main article: Cytoskeleton The cytoskeleton is an important, complex, and dynamic cell component. It acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell; and moves parts of the cell in processes of growth and motility. There are a great number of proteins associated with the cytoskeleton, each controlling a cell's structure by directing, bundling, and aligning filaments.

Genetic material

Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long term information storage, but some viruses (retroviruses) have RNA as their genetic material. The biological information contained 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 RNA for the genetic code itself. Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory). A human cell, e.g. has genetic material in the nucleus (the nuclear genome) and in the mitochondria (the mitochondrial genome). The nuclear genome is divided into 46 linear DNA molecules called chromosomes. The mitochondrial genome is a circular DNA molecule separate from the nuclear DNA. Although the mitochondrial genome is very small, it codes for some important proteins. Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is.

Organelles

Main article: Organelle The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs", called organelles, that are adapted and/or specialized for carrying out one or more vital functions. Membrane-bound organelles are only found in eukaryotes.
- Cell nucleus - a cell's information center: The cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes and is the place where almost all DNA replication and RNA synthesis occur. The nucleus is spheroid in shape and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. In prokaryotes, DNA processing takes place in the cytoplasm.
- Ribosomes - the protein production machine: Ribosomes are found in both prokaryotes and eukaryotes. The ribosome is a large complex composed of many molecules, including RNAs and proteins, and is responsible for processing the genetic instructions carried by an mRNA. The process of converting an mRNA's genetic code into the exact sequence of amino acids that make up a protein is called translation. Protein synthesis is extremely important to all cells, and therefore a large number of ribosomes—sometimes hundreds or even thousands—can be found throughout a cell.
- Mitochondria and chloroplasts - the power generators: Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. As mentioned earlier, mitochondria contain their own genome that is separate and distinct from the nuclear genome of a cell. Mitochondria play a critical role in generating energy in the eukaryotic cell, and this process involves a number of complex metabolic pathways. Chloroplasts are larger than mitochondria, and convert solar energy into a chemical energy ("food") via photosynthesis. Like mitochondria, chloroplasts have their own genome. Chloroplasts are found only in photosynthetic eukaryotes like plants and algae. There are a number of plant organelles that are modified chloroplasts; they are broadly called plastids and are often involved in storage.
- Endoplasmic reticulum and Golgi apparatus - macromolecule managers:: The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface, and the smooth ER, which lacks them. Translation of the mRNA for those proteins that will either stay in the ER or be exported from the cell occurs at the ribosomes attached to the rough ER. The smooth ER is important in lipid synthesis, detoxification and as a calcium reservoir. The Golgi apparatus, sometimes called a Golgi body or Golgi complex is the central delivery system for the cell and is a site for protein processing, packaging, and transport. Both organelles consist largely of heavily folded membranes.
- Lysosomes and peroxisomes - the cellular digestive system: Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally occurring proteins that speed up biochemical processes. For example, lysosomes can contain more than three dozen enzymes for degrading proteins, nucleic acids, and certain sugars called polysaccharides. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system.
- Centrioles - They help in the formation of mitotic appratus. Two centrioles are present in the animal cells. They are also found in some fungi and algae cells.
- Vacuoles-They store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane.

Anatomy of cells

Prokaryotic cells

Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack most of the intracellular organelles and structures that are characteristic of eukaryotic cells (an important exception is the ribosomes, which are present in both prokaryotic and eukaryotic cells). Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include:
- The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications beacon.
- Most prokaryotes have a cell wall (some exceptions are Mycoplasma (a bacterium) and Thermoplasma (an archaeon)). It consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" from osmotic pressure against a hypotonic environment. A cell wall is also present in some eukaryotes like fungi, but has a different chemical composition
- A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a real nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.

Eukaryotic cells

There are two types of cells, eukaryotic and prokaryotic. Eukaryotic cells are usally found in multi-cellular organisms, while prokaryotic cells are usually on their own. Eukaryotic cells are about 10 times the size of a typical prokaryote and can be as much as 1000 times greater in volume. The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote its name, which means "true nucleus." Other differences 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 highly condensed (i.e. folded around histones). All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles can contain some DNA.
- Eukaryotes can move using cilia or flagella. The flagella are more complex than those of prokaryotes.

Cell functions

Cell growth and metabolism

Main articles: Cell growth, Cell metabolism Between successive cell divisions cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions; catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, where the cell 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 molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, via two different pathways. The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction is designed 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 is capable of generating enough ATP to run all the cell functions.

Making new cells

Main article: Cell division Cell divisions (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.]] Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms. Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells 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 a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job.

Protein synthesis

Main article: Protein biosynthesis Protein synthesis is the process in which the cell builds proteins. DNA transcription refers to the synthesis of a messenger RNA (mRNA) molecule from a DNA template. This process is very similar to DNA replication. Once the mRNA has been generated, a new protein molecule is synthesized via the process of translation. The cellular machinery responsible for synthesizing proteins is the ribosome. The ribosome consists of structural RNA and about 80 different proteins. When the ribosome encounters an mRNA, the process of translating an mRNA to a protein begins. The ribosome accepts a new transfer RNA, or tRNA—the adaptor molecule that acts as a translator between mRNA and protein—bearing an amino acid, the building block of the protein. Another site binds the tRNA that becomes attached to the growing chain of amino acids, forming the a polypeptide chain that will eventually be processed to become a protein.

Origins of cells

Main article: Origin of life The origin of cells has to do with the origin of life, and was one of the most important steps in evolution of life as we know it. The birth of the cell marked the passage from prebiotic chemistry to biological life.

Origin of first cell

If life is viewed from the point of view of replicators, that is DNA molecules in the organism, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to maintain the fragile DNA chains stable in a varying and sometimes aggressive environment, and may have been the main reason for which cells evolved. The latter is fundamental for the evolution of biological complexity. If freely-floating DNA molecules that code for enzymes that are not enclosed into cells, the enzymes that advantage a given DNA molecule (for example, by producing nucleotides) will automatically advantage the neighbouring DNA molecules. This might be viewed as "parasitism by default". Therefore the selection pressure on DNA molecules will be much lower, since there is not a definitive advantage for the "lucky" DNA molecule that produces the better enzyme over the others: all molecules in a given neighbourhood are almost equally advantaged. If all the DNA molecule is enclosed in a cell, then the enzymes coded from the molecule will be kept close to the DNA molecule itself. The DNA molecule will directly enjoy the benefits of the enzymes it codes, and not of others. This means other DNA molecules won't benefit from a positive mutation in a neighbouring molecule: this in turn means that positive mutations give immediate and selective advantage to the replicator bearing it, and not on others. This is thought to have been the one of the main driving force of evolution of life as we know it. (Note. This is more a metaphor given for simplicity than complete accuracy, since the earliest molecules of life, probably up to the stage of cellular life, were most likely RNA molecules, acting both as replicators and enzymes: see RNA world hypothesis . But the core of the reasoning is the same.) Biochemically, cell-like spheroids formed by proteinoids are observed by heating amino acids with phosphoric acid as a catalyst. They bear much of the basic features provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could (but not necessarily should) have been the first cellular life forms on Earth. Another theory holds that the turbulent shores of the ancient coastal waters may have served as a mammoth laboratory, aiding in the countless experiments necessary to bring about the first cell. Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles comprised of mostly water tend to burst quickly, oily bubbles happen to be much more stable, lending more time to the particular bubble to perform these crucial experiments. The Phospholipid is a good example of a common oily compound prevalent in the prebiotic seas. Phospholipids can be constructed in ones mind as a hydrophilic head on one end, and a hydrophobic tail on the other. Phospholipids also possess an important characteristic, that is being able to link together to form a bilayer membrane. A lipid monolayer bubble can only contain oil, and is therefore not conducive to harbouring water-soluble organic molecules. On the other hand, a lipid bilayer bubble [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Phospholipids.html] can contain water, and was a likely precursor to the modern cell membrane. If a protein came along that increased the integrity of its parent bubble, then that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multi-celluar organisms could be achieved. This theory is expanded upon in the book, "The Cell: Evolution of the First Organism" by Joseph Panno Ph.D.

Origin of eukaryotic cells

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. It is almost certain that DNA-bearing organelles like the mitochondria and the chloroplasts are what remains of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where the rest of the cell seems to be derived from an ancestral archaean prokaryote cell – a theory termed the endosymbiotic theory. There is still considerable debate on if organelles like the hydrogenosome predated the origin of mitochondria, or viceversa : see the hydrogen hypothesis for the origin of eukaryotic cells.

History


- 1632-1723: Antony 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. ::...I could exceedingly plainly perceive it to be all perforated and porous, much like honeycomb...these pores or cells, were not very deep, but consisted of a great many little boxes... – Hooke describing his observations on a thin slice of cork.
- 1839 : Theodor Schwann and Matthias Jakob Schleiden elucidate the principal that plants and animals are made of cells, concluding that cells are a common unit of structure and development, thus founding the Cell Theory.
- The belief that life forms are able to occur spontaneously (generatio spontanea) is contradicted by Louis Pasteur (1822-1895).
- Rudolph 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.
- 1981: Lynn Margulis published Symbiosis in Cell Evolution detailing the endosymbiotic theory.

See also


- Cariology is the study of the cell nucleus.
- Cytotoxicity
- Plant cell
- How to prepare an onion cell slide
- Cell types
- Syncytium
- Cell culture
- Stem cell
- Plasmolysis
- Cytorrhysis

External links


- [http://www.ericdigests.org/2004-1/cells.htm Teaching about the Life and Health of Cells.]
- [http://www.biopic.co.uk/cellcity/cell.htm The cell like a city].
- [http://www.cellsalive.com/ Cells Alive!]
- [http://www.jcb.org/ Journal of Cell Biology]

References


- Category:Cell biology Category:Biology ko:세포 ms:Sel ja:細胞 simple:Cell th:เซลล์ (ชีววิทยา)

Light microscopy

Microscopy is any technique for producing visible images of structures or details too small to otherwise be seen by the human eye, using a microscope or other magnification tool. In classical light microscopy, this involves passing light transmitted through or reflected from the subject through a series of lenses, to be detected directly by the eye, imaged on a photographic plate or captured digitally. As resolution depends on the wavelength of the light, electron microscopy has been developed since the 1930's that use electron beams instead of light. Because of the much lower wavelength of the electron beam, resolution is far higher. Though less common, X-ray microscopy has also been developed since the late 1940's. The resolution of X-ray microscopy lies between that of light microscopy and the electron microscopy. Microscopy usually involves the diffraction, reflection, or refraction of radiation incident upon the subject of study. In some types of microscopy, the subject of study is imaged by scanning it line by line with a very fine physical probe (scanning probe microscopes). Examples of scanning probe microscopes are the atomic force microscope, the Scanning tunneling microscope and the photonic force microscope. The development of microscopy revolutionized biology and remains an essential tool in that science.

Types of Transmitted Light Microscopy

There are many different types of microscopes.

Light Microscopy: the contrast issue

Light microscopy can distinguish objects separated by down to 0.2 micrometers. Several optical configurations exist, depending on the amount of contrast a specimen under study needs.
- Bright field
- Dark field
- Phase contrast
- Differential interference contrast (DIC) LIVE cells in general lack sufficient contrast to be studied successfully. The problem here is that the internal structures of the cell are colourless and transparent ie without enough contrast to see detail. In a normal (brightfield) light microscope, contrast can generally be enhanced by closing the condenser aperture; however this will inherently reduce resolution to the point that the image becomes useless. The most obvious way is to stain the different structures with selective dyes, but this generally involves killing and fixing the material followed by staining. Every part can and generally will induce artefacts. With the lifesciences nowadays focussing on living cells, there was a need to develop optical methods to enhance the contrast. In general, these techniques make use of differences in refractive index of e.g. the different cell organelles. It is comparable to looking through a glass window: you don't see the glass but merely the dirt on the glass. There is however a difference as glass is a more dense material, and this creates a difference in phase of the light passing through. The human eye is not sensitive to this difference in phase but clever optical solutions have been thought out to change this difference in phase into a difference in amplitude (ie light intensity). Very old is the use of sideways (oblique) illumination, by covering part of the light entrance to the condenser. This method will give the specimen a sense of relief. A more recent technique based on this method is Hoffmann?s modulation contrast. This system is most often found on inverted microscopes for use in cell culture. Dark field illumination is another well known technique where a cone of light is being produced by the condenser that will not reach the objective. Minute particles will show up brightly on a dark background much like the dust that shows up in a beam of sunlight in an otherwise darkened room (Tyndal effect). More sophisticated techniques will show differences in optical density in proportion. Phase contrast is a widely used technique that shows differences in refractive index as difference in contrast. It was developed by the Dutch physicist Frits Zernike in the 1930's (for which he was awarded the Nobel Prize in 1953). The nucleus in a cell for example will show up darkly against the surrounding cytoplasm. Contrast is excellent; however it is not for use with thick objects. Frequently, a halo is formed even around small objects, which obscure detail. The system consists of a circular annulus in the condenser which produces a cone of light. This cone is superimposed on a similar sized ring within the phase-objective. Every objective has a different size ring, so for every objective another condenser setting has to be chosen. The ring in the objective has special optical properties: it first of all reduces the direct light in intensity, but more importantly, it creates an artificial phase difference of about a quarter wavelength. As the physical properties of this direct light have changed, interference with the diffracted light occurs, resulting in the phase contrast image. Superior and much more expensive is the use of interference contrast. Differences in optical density will show up as differences in relief. A nucleus within a cell will actually show up as a globule in the most often used differential interference contrast system according to Nomarski. However, it has to be kept in mind that this is an optical effect, and the relief does not necessarily resemble the true shape! Contrast is very good and the condenser aperture can be used fully open, thereby reducing the depth of field and maximising resolution. The system consists of a special prism in the condenser that splits light in a ?normal? and a ?reference? beam. The spatial difference between the two beams is minimal (less than the maximum resolution of the objective). After passage through the specimen, the beams are reunited by a similar prism in the objective. In a homogenous specimen, there is no difference between the two beams, and no contrast is being generated. However, near a refractive boundary (say a nucleus within the cytoplasm), the difference between the normal and the reference beam will generate a relief in the image. Differential interference contrast uses polarised light to work properly. Two polarising filters have to be fitted in the light path, one below the condenser (the polarizer), and the other above the objective (the analyser).

Fluorescence Microscopy

Fluorescence is the effect that certain compounds will send out light when illuminated with more energetic light. Often specimens show their own characteristic autofluorescence image, based on their chemical makeup. This method took a high flight in the modern lifesciences, as it can be extremely sensitive, with even detection of single molecules possible. Many different fluorescent dyes can be used to stain different structures or chemical compounds. Very powerful is the combination of antibodies coupled to a fluorochrome as in immunostaining. Examples of commonly used fluorochromes are fluorescein or rhodamine. The antibodies can be made very specific towards a chemical compound. For example, one strategy often in use nowadays is by producing proteins artificially, based on the genetic code (DNA). These proteins can then be used to immunize rabbits. The antibodies developed against those proteins are then coupled chemically to a fluorochrome and then used to trace back the proteins in the cells under study. Since recently, highly efficient fluorescent proteins such as the green fluorescent protein (GFP) can be specifically fused on DNA level to the protein of interest. This combined fluorescent protein is not toxic and hardly ever impedes the original task of the protein under study. Genetically modified cells or organisms directly express the fluorescently tagged proteins, which enables the study of the function of the original protein in vivo. Since fluorescence emission differs in wavelength (color) from the excitation light, a fluorescent image ideally only shows the structure of interest that was labelled with the fluorescent dye. This high specificity lead to the widespread use of fluorescence light microscopy in biomedical research. Different fluorescent dyes can be used to stain different biological structures, which can then be detected simultaneously still being specific due to the individual color of the dye. To block the excitation light from reaching the observed or the detector, filter sets of high quality are needed. These typically consist of an excitation filter selecting the range of excitation wavelengths, a dichroic mirror, and an emission filter blocking the excitation light. Most fluorescence microscopes are operated in the Epi-illumination mode (illumination and detection from one side of the sample) to further decrease the amount of excitation light entering the detector. See also total internal reflection fluorescence microscope.

Confocal scanning

:main article see Confocal laser scanning microscopy Generates the image by a completely different way than the normal visual bright field microscope. It gives slightly higher resolution, but most importantly it provides optical sectioning without disturbing out-of-focus light degrading the image. Therefore it provides sharper images of 3D objects. This is often used in conjunction with fluorescence microscopy. Removing unwanted out-of-focus light is also possible by computer based methods (deconvolution). By supplying a stack of images from a 3D object at different focal levels, it is possible to calculate which part of the image is out of focus and can then be removed from the image.

Electron microscopy

For Light Microscopy the wavelength of the light limits the resolution to around 0.2 micrometers. In order to gain higher resolution, the use of an electron beam with a far smaller wavelength is used in Electron Microscopes.
- Transmission electron microscopy (TEM) is principally quite similar to the compound light microscope, by sending an electron beam through a very thin slice of the specimen. The resolution limit nowadays (2005) is around 0.05 nanometer.
- Scanning electron microscopy (SEM) visualizes details on the surfaces of cells and particles and gives a very nice 3D view. It gives results much like the stereo light microscope and akin to that its most useful magnification is in the lower range then that of the transmission electron microscope.

External links


- [http://www.biologie.uni-hamburg.de/b-online/e03/03.htm Microscopy in Detail] - A resource with many illustrations elaborating the most common microscopy techniques
- [http://www.confocal-microscopy.org Confocal microscopy theory and protocols]
- [http://micro.magnet.fsu.edu/primer/techniques/darkfield.html Dark field microscopy page from FSU]
- [http://www.scienceofspectroscopy.info The Science of Spectroscopy] - supported by NASA, includes OpenSpectrum, a spectroscopy Wiki
- [http://brainmaps.org Microscopic images of primate and non-primate brains]
- Category:Laboratory techniques

Biopsy

A biopsy (in Greek: bios = life and opsy = look/appearance) is a medical test involving the removal of cells or tissues for examination. The tissue is often examined under a microscope and can also be analyzed chemically (for example, using PCR techniques). Biopsy specimens are often taken from part of a lesion when the cause of a disease is uncertain or its extent or exact character is in doubt. Vasculitis, for instance, is usually diagnosed on biopsy. Additionally, pathologic examination of a small biopsy can help differentiate between different types of cancer and determine whether a lesion is benign or malignant. In contrast to a biopsy that merely samples a lesion, a larger excisional specimen called a resection may come to a pathologist, typically from a surgeon attempting to eradicate a known lesion from a patient. For example, a pathologist would examine a mastectomy specimen, even if a previous nonexcisional breast biopsy had already established the diagnosis of breast cancer. Examination of the full mastectomy specimen would confirm the exact nature of the cancer (subclassification of tumor and histologic "grading") and reveal the extent of its spread (pathologic "staging"). When only a sample of tissue is removed, the procedure is called an incisional biopsy or core biopsy. When an entire lump or suspicious area is removed, the procedure is called an excisional biopsy. When a sample of tissue or fluid is removed with a needle, the procedure is called a needle aspiration biopsy. See also: pathology, autopsy Category:Medical tests

B cell

B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). The abbreviation "B" stands for the bursa of Fabricius which is an organ unique to birds, where B cells mature. It does not stand for bone marrow, where B cells are produced in all other vertebrates except for rabbits (where B cells develop in the appendix-sacculus rotundus). The human body makes millions of different types of B cells each day, and each type has a unique receptor protein (referred to as the B cell receptor, or the BCR) on its membrane that will bind to one particular antigen; at any one time in the human body millions of B cells are circulating in the blood and lymph, but are not producing antibodies. Once the B cell encounters its cognate antigen and receives an additional signal from a helper T cell, it can further differentiate into one of the two types of B cells listed below. The B cell can either directly become one of these cell types or go through an intermediate differentiation step - the germinal center reaction where the B cell will hypermutate the variable region of the antibody and possibly class switch.
- Plasma B cells secrete antibodies which affect the destruction of antigens by binding to them and making them easier targets for phagocytes (a process known as opsonization).
- Memory B cells are formed specific to the antigen(s) encountered during the primary immune response; able to live for a long time, these cells can respond quickly upon second exposure to the antigen for which they are specific. Humoral immunity (the creation of antibodies that circulate in blood plasma and lymph) involves B cell activation. Cell activation can be gauged using the ELISPOT technique, which can determine the percentage of B cells that secrete any particular antibody. B cells are characterised immunohistochemically in humans by the presence of CD20 on the cell membrane. In mice, CD45 (B220) is often used. A critical difference between B cells and T cells is how each cell "sees" antigen. B cells recognize their cognate antigen in its native form. In contrast, T cells recognize their cognate antigen in a processed form - as a peptide in the context of an MHC molecule. Susumu Tonegawa won the 1987 Nobel Prize in Physiology or Medicine for demonstrating how B cells create the enormous diversity of antibodies from only a few genes.

Production of B Cells

B cells are produced through several stages, each stage represents a change in the genome content, in which the variety of antibodies are produced. The human antibody is composed of two light and two heavy chains, and there are genes specifying them, which is known as the 'H' chain loci and the 'L' chain loci. In the H chain loci there are three regions, V, D and J, and combinations of threes are drawn, in terms of rearrangement which results in deletions of bases between the two selected points, and results in formation of a unique combination. In the L chain loci there are only two regions, namely V and J, which undergoes the same process.
- Progenitor B cells - Contains Germline H genes, Germline L genes
- Early Pro-B cells - undergoes D-J rearrangement on the H chains
- Late Pro-B cells - undergoes V-DJ rearrangement on the H chains
- Large Pre-B cells - the H chain is VDJ rearranged, Germline L genes
- Small Pre-B cells - undergoes V-J rearrangement on the L chains
- Immature B cells - VJ rearranged on L chains, VDJ rearranged on H chains. There is start of expression of IgM receptors.
- Mature B cells - There is start of expression of IgD When the B cells fails in any step of the maturation process, it will undergo apoptosis, and if it recognize self-antigen during the maturation process, it will become suppressed (known as anergy) or undergo apoptosis. B cells are continuously produced in the bone marrow, but only a small portion of newly made B cells survive to participate a part in the long-lived peripheral B cell pool.

See also


- T lymphocyte
- Antibody Category:Lymphocytes ko:B세포 ja:B細胞

Cell nucleus

In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cell's genetic material. Nuclei have two primary functions: to control chemical reactions within the cytoplasm and to store information needed for cellular division. Aside from containing the cell's genome, the nucleus contains certain proteins whose interplay is thought to regulate the expression of genes. Gene expression at the nuclear level involves complex processes of transcription, pre mRNA processing and the export of the mature mRNA to the cytoplasm. The nucleus varies in diameter from 11 to 22.25 micrometres. It is enclosed by a double membrane called the nuclear envelope. The inner and outer membrane fuse at regular intervals, forming nuclear pores. The nuclear envelope regulates and facilitates transport between the nucleus and the cytoplasm, while separating the chemical reactions taking place in cytoplasm from reactions happening within the nucleus. The outer membrane is continuous with the rough endoplasmic reticulum (RER) and may be studded with ribosomes. The space between the two membranes (called the "perinuclear space") is continuous with the lumen of the RER. The nuclear face of the nuclear envelope is surrounded by a scaffold of filaments called the nuclear lamina. nuclear lamina (2) Ribosomes (3) Nuclear pore complexes (4) Nucleolus (5) Chromatin (6) Nucleus (7) Endoplasmic reticulum (8) Nucleoplasm
The whole structure is surrounded by cytoplasm. (Drawing is based on ER images.) ]] Inside the nucleus is one or several nucleoli surrounded by a matrix called the nucleoplasm. The nucleoplasm is a liquid with a gel-like consistency (similar in this respect to the cytoplasm), in which many substances are dissolved. These substances include nucleotide triphosphates, enzymes, proteins, and transcription factors. There also exists a network of fibers in the nucleoplasm known as the nuclear matrix. Genetic material (DNA) is also present in the nucleus, the DNA is present as a DNA-protein complex called chromatin. The DNA is present as a number of discrete units known as chromosomes. There are two types of chromatin: euchromatin and heterochromatin. Euchromatin is the least compact form of DNA, and the regions of DNA which constitute euchromatin contain genes which are frequently expressed by the cell. In heterochromatin, DNA is more tightly compacted. Regions of DNA which constitute heterochromatin generally contain genes which are not expressed by the cell (this type of heterochromatin is known as facultative heterochromatin) or are regions which make up the telomeres and centromeres of the chromosomes (this type of heterochromatin is known as constitutive heterochromatin). In multicellular organisms, cells are highly specialised to perform particular functions, hence different sets of genes are required and expressed. Therefore, the regions of DNA that constitute heterochromatin vary between cell types.

Nucleoli

Nucleoli are densely-stained structures in the nucleus where ribosome subunits are assembled. Category:Organelles ms:Nukleus ja:細胞核

Eosinophilic

Eosinophilic is a technical term used by histologists. The context in which this word is used is in describing the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with the dye eosin. Eosinophilic describes the appearance of cells and structures seen in histological sections which take up the staining dye, eosin. This is a bright pink dye that stains the cytoplasm of cells as well as extracellular proteins such as collagen. Such eosinophilic structures are generally composed of protein. The stain eosin is usually combined with a stain called haematoxylin to produce a haematoxylin and eosin stained section (also called an H&E, HE or H+E section). This is the most widely used histological stain in medical diagnosis - for example when a pathologist looks at a biopsy of a suspected cancer they will have the section stained with H&E. Some structures seen inside cells are described as being eosinophilic, for example Lewy bodies, Mallory bodies.

See also


- basophilic (affinity to hematoxylln) Category:Anatomical pathology

Nucleolus

In biology, the nucleolus is, strictly speaking, a "suborganelle" of the nucleus, which is an organelle. Most plant and animal cells have one or more nucleoli although some do not. No membrane separates the nucleolus from the nucleoplasm. Nucleoli are made of protein and ribonucleic acid (RNA) and contain proteins as well as ribosomal RNA. It is known that they carry out the production and maturation of ribosomes; additional functions have also been suggested. The nucleolus consists of three distinct regions: the fibrillar centres, the dense fibrillar component and the granular component. It is a consequence of ribosomal RNA (rRNA) synthesis: nucleolar organizers, special regions known as nuclear organizing regions (NOR) on some chromosomes that contain multiple copies of the genes encoding for rRNA (which is involved in protein biosynthesis), gather themselves in the same region where they transcribe the rRNA genes. Thus it can be said the nucleolus consists basically of nucleolar organizers and the transcribed rRNA (plus associated proteins). Following synthesis, rRNA molecules are attached to proteins, forming ribosomal subunits, which leave for the cytosol through nuclear pores. These nuclear pores are known as the Nuclear Pore Complex (NPC). The nucleolus disappears during cell reproduction, because there is no need for ribosomes. The nucleolus is reformed when the cells complete their formation and begin moving their chromosomes into nucleolar organizing regions. Category:Organelles ja:核小体

Cluster of differentiation

Cluster of differentiation (CD) molecules are markers on the cell surface, as recognized by specific sets of antibodies, used to identify the cell type, stage of differentiation and activity of a cell.

Nomenclature

The CD nomenclature was proposed and established in the 1st International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA), which was held in Paris in 1982. This system was intended for the classification of the many monoclonal antibodies (mAbs), generated by different laboratories around the world, against various surface molecules (antigens) on leukocytes (white blood cells). Since then, the use has expanded to many other cell types, and more than 250 CD clusters and subclusters have been identified. The HLDA workshops assign each CD based on the same reactivity to one human antigen by at least two mAbs; the provisional indicator "w" (as in "CDw186") is sometimes given to a cluster not well characterized or represented by only one mAb.

Uses


- CD molecules are often referred to when sorting cells by flow cytometry. A '+' or a '–' symbol is used to indicate if a certain fraction of cells possesses or lacks a CD molecule; for example, a "CD34+, CD31–" cell is one that expresses CD34, but not CD31.
- The most commonly referred to CD molecules are CD4 and CD8, which are markers for two different subtypes of T-lymphocytes, for the most part (Dendritic cells also express CD8). The relative abundance of CD4+ and CD8+ T cells is often used to monitor the progression of an HIV infection.
- CD molecules are not merely markers on the cell surface. Not every CD molecule has been thoroughly characterised, but most of them bring important features to the cells that carry them. In the example of CD4 & CD8, these molecules are critical in the antigen recognition pathway.

See Also


- List of human clusters of differentiation for a list of CD molecules

External links


- [http://www.mh-hannover.de/aktuelles/projekte/hlda7/hldabase/select.htm HLDA Antibody Database]
- A [http://www.ebioscience.com/ebioscience/whatsnew/humancdchart.htm list of CD molecules], at ebioscience.com
- Another [http://ca.expasy.org/cgi-bin/lists?cdlist.txt list of CD molecules], at Expasy.org
- Yet another [http://pathologyoutlines.com/cdmarkers.html list of CD molecules], at PathologyOutlines.com
- [http://www.rndsystems.com/molecule_letter.aspx?l=C Catalogue of some CD-factors], as R&D Systems. Category:Anatomical pathology Category:Immunology

Cluster of differentiation

Cluster of differentiation (CD) molecules are markers on the cell surface, as recognized by specific sets of antibodies, used to identify the cell type, stage of differentiation and activity of a cell.

Nomenclature

The CD nomenclature was proposed and established in the 1st International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA), which was held in Paris in 1982. This system was intended for the classification of the many monoclonal antibodies (mAbs), generated by different laboratories around the world, against various surface molecules (antigens) on leukocytes (white blood cells). Since then, the use has expanded to many other cell types, and more than 250 CD clusters and subclusters have been identified. The HLDA workshops assign each CD based on the same reactivity to one human antigen by at least two mAbs; the provisional indicator "w" (as in "CDw186") is sometimes given to a cluster not well characterized or represented by only one mAb.

Uses


- CD molecules are often referred to when sorting cells by flow cytometry. A '+' or a '–' symbol is used to indicate if a certain fraction of cells possesses or lacks a CD molecule; for example, a "CD34+, CD31–" cell is one that expresses CD34, but not CD31.
- The most commonly referred to CD molecules are CD4 and CD8, which are markers for two different subtypes of T-lymphocytes, for the most part (Dendritic cells also express CD8). The relative abundance of CD4+ and CD8+ T cells is often used to monitor the progression of an HIV infection.
- CD molecules are not merely markers on the cell surface. Not every CD molecule has been thoroughly characterised, but most of them bring important features to the cells that carry them. In the example of CD4 & CD8, these molecules are critical in the antigen recognition pathway.

See Also


- List of human clusters of differentiation for a list of CD molecules

External links


- [http://www.mh-hannover.de/aktuelles/projekte/hlda7/hldabase/select.htm HLDA Antibody Database]
- A [http://www.ebioscience.com/ebioscience/whatsnew/humancdchart.htm list of CD molecules], at ebioscience.com
- Another [http://ca.expasy.org/cgi-bin/lists?cdlist.txt list of CD molecules], at Expasy.org
- Yet another [http://pathologyoutlines.com/cdmarkers.html list of CD molecules], at PathologyOutlines.com
- [http://www.rndsystems.com/molecule_letter.aspx?l=C Catalogue of some CD-factors], as R&D Systems. Category:Anatomical pathology Category:Immunology

Category:Anatomical pathology

Anatomical pathology is a specialty of medicine that deals with diagnosing disease by examining tissue that is affected by it, either through gross pathology or by light microscopy and other advanced techniques. Category:Medical specialties Category:Anatomy Category:Pathology

Category:Eponymous anatomical structures

These are anatomical structures in the human body that are eponymously named after a person, usually the person who first described them. See also: List of human anatomical parts named after people Category:Eponymous medical terms Category:Anatomy

Garstedt

Dieser Artikel beschreibt die Gemeinde Garstedt, für den gleichnamigen Ortsteil Norderstedt, siehe dort. ---- Garstedt ist eine Gemeinde in der Samtgemeinde Salzhausen im Landkreis Harburg, Niedersachsen (Deutschland). Sie hat eine Lage von: 30 km südlich der Stadtgrenze zu Hamburg. 1252 wurde sie erstmalig urkundlich erwähnt. Mittlerweile hat sie ca. 1.500 Einwohner.
- Geografische Koordinaten:
- Kfz-Kennzeichen WL
- Postleitzahl(en) 21441
- 11 Ratsmitglieder: 6 x UWG (Unabhängige Wählergemeinschaft Garstedt) 3 x CDU 2 x SPD Die Gemeinde Garstedt, gelegen am Rande der Lüneburger Heide, zwischen Winsen/Luhe und Salzhausen, ist ein Paradies für die Naherholung und bietet Ruhe für den Erholung suchenden Urlauber. Vielfältige Möglichkeiten heben die Attraktivität dieses kleinen Ortes. Die abwechslungsreiche Landschaft mit Wald - Heide - Wiese - Berg und Tal laden zum Wandern, Spazierengehen und Radfahren ein. In dem weitläufigen Gelände kommen auch Reitsportler auf ihre Kosten und internationale Pferde-Turniere können im nahegelegenen Luhmühlen besucht werden. Die Nähe der Luhe lädt zum Wasserwandern mit den Kanus, Kajaks oder Faltbooten ein oder auch zum Baden im klaren Wasser der Luhe. Und im Winter, wenn Schnee vorhanden ist, können Jung und Alt am Hamberg auf der Roddelpiste Ihren Spaß haben. Die örtliche Grundversorgung ist durch Lebensmitteleinkäufe am Ort gewährleistet. Arzt, Apotheke, Banken, KFZ-Betrieb und Tankstelle sind im angegrenzenden Ort Wulfsen vorhanden. Im 10km entfernten Salzhausen sind weitere und weitergehende Einkaufsmöglichkeiten, inkl. einem Krankenhaus und weiterführende Schulformen (Haupt-, Realschule und Gymnasium) vorhanden. Die Städte Winsen/Luhe (15 km), Lüneburg (20km) und Hamburg (40km) sind schnell erreichbar.

Weblinks


- [http://www.garstedt.de/ Website der Gemeinde] Kategorie:Ort in Niedersachsen

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