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By Dr Ananya Mandal, MD
Embryology is the study of development of an embryo from the stage of ovum fertilization through to the fetal stage.
The ball of dividing cells that results after fertilization is termed an embryo for eight weeks and from nine weeks after fertilization, the term used is fetus.
Once an egg is released from the ovary during ovulation, it meets with a sperm cell that was carried to it via the semen. These two gametes combine to form a zygote and this process is called fertilization. The zygote then begins to divide and becomes a blastula.
The blastula develops in one of two ways, which actually divides the whole animal kingdom in half. The blastula develops a pore at one end, called a blastopore. If that blastopore becomes the mouth of the animal, the animal is a protostome, and if it forms an anus, the animal is a deuterostome.
Protosomes are invertebrate animals such as worms, insects and molluscs while deuterostomes are vertebrates such as birds, reptiles, and humans.
The blastula continues to develop, eventually forming a structure called the gastrula. The gastrula then forms three germ cell layers, from which all of the bodys organs and tissues are eventually derived. From the innermost layer or endoderm, the digestive organs, lungs and bladder develop; the skeleton, blood vessels and muscles are derived from the middle layer or mesoderm and the outer layer or ectoderm gives rise to the nervous system, skin and hair.
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British Dictionary definitions for embryology Expand
the branch of science concerned with the study of embryos
the structure and development of the embryo of a particular organism
Derived Forms
embryological (mbrldkl), embryologic, adjectiveembryologically, adverbembryologist, noun
Word Origin and History for embryology Expand
1859, from embryon (see embryo) + -logy. Related: Embryologist (c.1850).
embryology in Medicine Expand
embryology embryology (m'br-l'-j) n.
The branch of biology that deals with the formation, early growth, and development of living organisms.
The embryonic structure or development of an organism.
embryology in Science Expand
embryology in Culture Expand
The study of the embryo; a major field of research in modern biology.
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This article is about the development of embryos in animals. For the development of plant embryos, see Sporophyte.
Embryology (from Greek , embryon, "the unborn, embryo"; and -, -logia) is the branch of biology that studies the development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology is the study of congenital disorders that occur before birth.[1]
After cleavage, the dividing cells, or morula, becomes a hollow ball, or blastula, which develops a hole or pore at one end.
In bilateral animals, the blastula develops in one of two ways that divides the whole animal kingdom into two halves (see: Embryological origins of the mouth and anus). If in the blastula the first pore (blastopore) becomes the mouth of the animal, it is a protostome; if the first pore becomes the anus then it is a deuterostome. The protostomes include most invertebrate animals, such as insects, worms and molluscs, while the deuterostomes include the vertebrates. In due course, the blastula changes into a more differentiated structure called the gastrula.
The gastrula with its blastopore soon develops three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop:
Embryos in many species often appear similar to one another in early developmental stages. The reason for this similarity is because species have a shared evolutionary history. These similarities among species are called homologous structures, which are structures that have the same or similar function and mechanism, having evolved from a common ancestor.
Click here to read the main article on Drosophila embryogenesis
Drosophila melanogaster, a fruit fly, is a model organism in biology on which much research into embryology has been done (see figure 1.1.1A and figure 1.1.1B).[2] Before fertilization, the female gamete produces an abundance of mRNA - transcribed from the genes that encode bicoid protein and nanos protein.[3][4] These mRNA molecules are stored to be used later in what will become a developing embryo. The male and female Drosophila gametes exhibit anisogamy (differences in morphology and sub-cellular biochemistry). The female gamete is larger than the male gamete because it harbors more cytoplasm and, within the cytoplasm, the female gamete contains an abundance of the mRNA previously mentioned.[5][6] At fertilization, the male and female gametes fuse (plasmogamy) and then the nucleus of the male gamete fuses with the nucleus of the female gamete (karyogamy). Note that before the gametes' nuclei fuse, they are known as pronuclei.[7] A series of nuclear divisions will occur without cytokinesis (division of the cell) in the zygote to form a multi-nucleated cell (a cell containing multiple nuclei) known as a syncytium.[8][9] All the nuclei in the syncytium are identical, just as all the nuclei in every somatic cell of any multicellular organism are identical in terms of the DNA sequence of the genome.[10] Before the nuclei can differentiate in transcriptional activity, the embryo (syncytium) must be divided into segments. In each segment, a unique set of regulatory proteins will cause specific genes in the nuclei to be transcribed. The resulting combination of proteins will transform clusters of cells into early embryo tissues that will each develop into multiple fetal and adult tissues later in development (note: this happens after each nucleus becomes wrapped with its own cell membrane).
Outlined below is the process that leads to cell and tissue differentiation.
Maternal-effect genes - subject to Maternal (cytoplasmic) inheritance.
Zygotic-effect genes - subject to Mendelian (classical) inheritance.
Humans are bilaterals and deuterostomes.
In humans, the term embryo refers to the ball of dividing cells from the moment the zygote implants itself in the uterus wall until the end of the eighth week after conception. Beyond the eighth week after conception (tenth week of pregnancy), the developing human is then called a fetus.
As recently as the 18th century, the prevailing notion in western human embryology was preformation: the idea that semen contains an embryo a preformed, miniature infant, or homunculus that simply becomes larger during development. The competing explanation of embryonic development was epigenesis, originally proposed 2,000 years earlier by Aristotle. Much early embryology came from the work of the Italian anatomists Aldrovandi, Aranzio, Leonardo da Vinci, Marcello Malpighi, Gabriele Falloppio, Girolamo Cardano, Emilio Parisano, Fortunio Liceti, Stefano Lorenzini, Spallanzani, Enrico Sertoli, and Mauro Rusconi.[22] According to epigenesis, the form of an animal emerges gradually from a relatively formless egg. As microscopy improved during the 19th century, biologists could see that embryos took shape in a series of progressive steps, and epigenesis displaced preformation as the favoured explanation among embryologists.[23]
Karl Ernst von Baer and Heinz Christian Pander proposed the germ layer theory of development; von Baer discovered the mammalian ovum in 1827.[24][25][26] Modern embryological pioneers include Charles Darwin, Ernst Haeckel, J.B.S. Haldane, and Joseph Needham. Other important contributors include William Harvey, Kaspar Friedrich Wolff, Heinz Christian Pander, August Weismann, Gavin de Beer, Ernest Everett Just, and Edward B. Lewis.
After the 1950s, with the DNA helical structure being unravelled and the increasing knowledge in the field of molecular biology, developmental biology emerged as a field of study which attempts to correlate the genes with morphological change, and so tries to determine which genes are responsible for each morphological change that takes place in an embryo, and how these genes are regulated.
Many principles of embryology apply to invertebrates as well as to vertebrates.[27] Therefore, the study of invertebrate embryology has advanced the study of vertebrate embryology. However, there are many differences as well. For example, numerous invertebrate species release a larva before development is complete; at the end of the larval period, an animal for the first time comes to resemble an adult similar to its parent or parents. Although invertebrate embryology is similar in some ways for different invertebrate animals, there are also countless variations. For instance, while spiders proceed directly from egg to adult form, many insects develop through at least one larval stage.
Currently, embryology has become an important research area for studying the genetic control of the development process (e.g. morphogens), its link to cell signalling, its importance for the study of certain diseases and mutations, and in links to stem cell research.
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embryology [embre-olo-je]
the science of the development of the individual during the embryonic stage and, by extension, in several or even all preceding and subsequent stages of the life cycle. adj., adj embryologic.
Science of the origin and development of the organism from fertilization of the oocyte to the end of the eighth week. Usually used to include all stages of prenatal life.
[embryo- + G. logos, study]
1. The branch of biology that deals with the formation, early growth, and development of living organisms.
2. The embryonic structure or development of an organism.
Etymology: Gk, en, bryein + logos, science
Science of the origin and development of the organism from fertilization of the oocyte to the end of the eighth week and, by extension, all subsequent stages up to birth.
[embryo- + G. logos, study]
Science of the origin and development of the organism from fertilization of the oocyte to the end of the eighth week.
[embryo- + G. logos, study]
(embrolj), n the study of the origin, growth, development, and function of an organism from fertilization to birth.
the science of the development of the individual animal during the embryonic stage and, by extension, in several or even all preceding and subsequent stages of the life cycle.
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Embryology is the branch of developmental biology that studies embryos and their development. The field of developmental biology encompasses the overall study of the process by which organisms grow and develop, including cell growth, cellular differentiation, and, "morphogenesis," which is the process that gives rise to tissues, organs, and anatomy. Embryology, a subfield of developmental biology, is the study of organisms between the one-cell stage (generally, the zygote) and the end of the embryonic stage, which is not necessarily the beginning of free living.
Embryology was originally a more descriptive science until the twentieth century. Embryology and developmental biology today deal with the various steps necessary for the correct and complete formation of the body of a living organism.
The wonder by which a single, fertilized egg differentiates into diverse cells, tissues, organs, and systems of a fully formed organismthe heart, lungs, brain, arms, endocrine system, muscles, and bones of a human, for instanceremains a mystery that embryologists attempt to unravel.
Embryology is the classic study of morphological changes within the embryo. Aristotle is said to be the first person to undertake a study in embryology. Aristotle observed the ontogeny of chicken embryos by breaking open eggs at various time intervals during incubation.
In the 1950s, with the discovery of the structure of DNA by Watson and Crick, and the rapidly increasing knowledge in molecular biology, developmental biology emerged as a field of study interested in the role that genes play in development. In other words, developmental biologists wanted to know which genes are responsible for each morphological change that occurs in development. Perhaps even more importantly, developmental biologists sought to explain how the various cell types of a multicellular organism arise from a single fertilized cell, the egg.
Development of an embryo can be divided into several stages. The first stage is fertilization, in which the sperm penetrates the egg. The nuclei of the sperm and egg then fuse to form a diploid zygote (with paired chromosomes). Cleavage follows, in which the single cell composing the embryo undergoes mitosis (cell division), resulting in many cells called blastomeres. Each blastomere has the exact same genome (set of DNA) as the zygote. These blastomeres come to compose a solid ball of cells called a morula. The final event of cleavage involves the formation of a blastula, or a hollow ball of blastomeres containing a blastocoel, or fluid-filled cavity.
Gastrulation is the stage in which the blastomeres partition themselves into three distinct germ layers: the ectoderm, mesoderm, and endoderm. The ectoderm is the outermost layer and will eventually develop to form the skin and nervous system. The endoderm is the innermost layer and will eventually develop to form the lining of the gut and internal organs. The mesoderm is the middle layer, which eventually forms the muscles, bones, and heart.
After the forming of the gastrula (the multi-layered structure formed during gastrulation), the cells begin to differentiate, or undergo physical and chemical changes that will determine their individual identities (as muscle cells, kidney cells, etc.). Growth is the last stage, in which cells divide and proliferate, eventually composing all the major organs of the body.
One of the significant questions that early developmental biologists sought to answer was how cell individuation occurs. Almost every cell in the body contains the exact same DNA as every other cell, as they all are derived from the initial zygotic cell. So how is it that some cells become cardiac cells and others become skin cells?
One explanation offered for this question is termed induction, the process whereby the development of a cell, or the fate of a group of cells, is influenced by neighboring cells.
The early development of an egg is influenced by the mother. When an egg is first fertilized, its cytoplasm contains lots of the mothers RNA and proteins. In fact, the fertilized egg does not actually start to transcribe its own DNA until the blastula contains about 4,000 cells. The mothers RNA and proteins are not dispersed homogenously throughout the eggs cytoplasm. Instead, they form gradients, so that each section of the egg has a particular selection and quantity of the mothers RNA and proteins. This is called the maternal effect.
When cleavage events occur, different groups of cells in the blastula are exposed to different environments from one another. The different environments consist of different selections and quantities of the mothers RNA and proteins. The mothers RNA and proteins act as signals for the cells, telling the cells which genes to turn on or off. Thus, because different cells will receive different signals, they will develop differently via cell-intrinsic signals and will produce individual signals of their own.
Induction is held to occur when a cell produces a certain signal, for example, by emitting a protein. The protein may diffuse around the cell source. Cells that are closely neighboring the source will receive lots of the signal, while more distant cells will receive less or none of the signal. Therefore, cells will develop different characteristics and functions depending on their relative location to other cells, and thus their individual cell-cell interactions.
Although the phenomena of induction provides insights into how cells individually differentiate into diverse structures, a comprehensive understanding of this process, from an individual egg cell to particular organs, lacks consensus. Notably, some developmental biologists question an underlying assumption of embryonic development that genes ultimately direct the changes, maintaining that the genetic matter only determines which proteins can be produced, but not the form of the organisms (Wells 1997).
Scientists often use model organisms (a species that is extensively studied to understand particular biological phenomena) to learn about how development occurs in animals generally. Although all species develop somewhat differently, there are also many similarities that occur in development in species. For example, certain groups of genes are conserved between humans and flies and worms. Some common examples of model organisms are the fruit fly Drosophila melanogaster, Caenorhabditis elegans (nematode worm), E. coli, the mouse, the zebrafish, and many others.
Ontogeny (also ontogenesis or morphogenesis) is a term that describes the origin and the development of an organism from the fertilized egg to its mature form. Ontogeny is studied in developmental biology.
In 1866, German zoologist Ernst Haeckel theorized that "ontogeny recapitulates phylogeny" (the evolutionary history of a species), and this theory (which was also independently established by others) became known as the biogenetic law or the theory of recapitulation. The idea that ontogeny recapitulates phylogeny, that is, that the development of an organism exactly mirrors the evolutionary development of the species, repeating the adult forms of the organisms, is discredited today. Likewise discredited is the ancillary principle that the there is "terminal addition"evolution proceeding by adding stages to the end of the ancestral organisms (Gould 1977).
However the phenomenon by which a developing organism will for a time show a similar trait or attribute to that of an ancestral species, only to have it disappear at a later stage, is well documented. That is, embryos seem to repeat the embryonic stages (not adult stages) of their ancestors. For example, embryos of the baleen whale exhibit teeth at certain embryonic stages, only to later disappear. A more commonly given example is the emergence of pharyngeal gill pouches of lower vertebrates in almost all mammalian embryos at early stages of development (April, 2001). Note, however, in terms of this later example, some embryologists state the resemblance of pharyngeal pouches in mammals to the gill clefts of fish is illusory, and there is no embryological reason to make such a claim (Wells 2000).
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Embryology,vertebrate embryosEncyclopdia Britannica, Inc.the study of the formation and development of an embryo and fetus. Before widespread use of the microscope and the advent of cellular biology in the 19th century, embryology was based on descriptive and comparative studies. From the time of the Greek philosopher Aristotle it was debated whether the embryo was a preformed, miniature individual (a homunculus) or an undifferentiated form that gradually became specialized. Supporters of the latter theory included Aristotle; the English physician William Harvey, who labeled the theory epigenesis; the German physician Caspar Friedrick Wolff; and the Prussian-Estonian scientist Karl Ernst, Ritter von Baer, who proved epigenesis with his discovery of the mammalian ovum (egg) in 1827. Other pioneers were the French scientists Pierre Belon and Marie-Franois-Xavier Bichat.
Baer, who helped popularize Christian Heinrich Panders 1817 discovery of primary germ layers, laid the foundations of modern comparative embryology in his landmark two-volume work ber Entwickelungsgeschichte der Thiere (182837; On the Development of Animals). Another formative publication was A Treatise on Comparative Embryology (188091) by the British zoologist Frances Maitland Balfour. Further research on embryonic development was conducted by the German anatomists Martin H. Rathke and Wilhelm Roux and also by the American scientist Thomas Hunt Morgan. Roux, noted for his pioneering studies on frog eggs (beginning in 1885), became the founder of experimental embryology. The principle of embryonic induction was studied by the German embryologists Hans Adolf Eduard Driesch, who furthered Rouxs research on frog eggs in the 1890s, and Hans Spemann, who was awarded a Nobel Prize in 1935. Ross G. Harrison was an American biologist noted for his work on tissue culture.
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.
1. The branch of biology that deals with the formation, early growth, and development of living organisms.
2. The embryonic structure or development of a particular organism.
embryologic (--ljk), embryological adj.
embryologically adv.
embryologist n.
1. (Biology) the branch of science concerned with the study of embryos
2. (Biology) the structure and development of the embryo of a particular organism
n., pl. -gies.
1. the study of embryonic formation and development.
2. the origin, growth, and development of an embryo: the embryology of the chick.
[184050]
em`bryological (-ld kl) em`bryologic, adj.
em`bryologically, adv.
em`bryologist, n.
The branch of biology that deals with embryos and their development.
Study of development of embryos.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Translations
n. embriologa, estudio del embrin y su desarrollo hasta el momento del nacimiento.
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Embryology - definition of embryology by The Free Dictionary
Cell biology (formerly cytology, from the Greek , kytos, "contain") is a branch of biology that studies cells their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division, death and cell function. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans, plants, and sponges.
Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.
Each type of protein is usually sent to a particular part of the cell. An important part of cell biology is the investigation of molecular mechanisms by which proteins are moved to different places inside cells or secreted from cells.
Most proteins are synthesized by ribosomes in the rough endoplasmic reticulum (RER). Ribosomes contain the nucleic acid RNA, which assembles and joins amino acids to make proteins. They can be found alone or in groups within the cytoplasm as well as on the RER. This process is known as protein biosynthesis. Biosynthesis (also called biogenesis) is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products (also simply known as protein translation). Some proteins, such as those to be incorporated in membranes (known as membrane proteins), are transported into the RER during synthesis. This process can be followed by transportation and processing in the Golgi apparatus. The Golgi apparatus is a large organelle that processes proteins and prepares them for use both inside and outside the cell. The Golgi apparatus is somewhat like a post office. It receives items (proteins from the ER), packages and labels them, and then sends them on to their destinations (to different parts of the cell or to the cell membrane for transport out of the cell).[1] From the Golgi, membrane proteins can move to the plasma membrane, to other sub-cellular compartments, or they can be secreted from the cell. The endoplasmic reticulum (ER) and Golgi can be thought of as the "membrane protein synthesis compartment" and the "membrane protein processing compartment", respectively. There is a semi-constant flux of proteins through these compartments. ER and Golgi-resident proteins associate with other proteins but remain in their respective compartments. Other proteins "flow" through the ER and Golgi to the plasma membrane. Motor proteins transport membrane protein-containing vesicles along cytoskeletal tracks to distant parts of cells such as the axon terminals of neurons.
A notable mode of protein transport occurs through the vesicles discussed above. Vesicles are formed by membrane bulges that pinch off, carrying protein with them to another component, may it be the cell membrane or another organelle. This allows proteins to be moved without having to truly cross a membrane.[2]
Some proteins that are made in the cytoplasm contain structural features that target them for transport into mitochondria or the cell nucleus. Some mitochondrial proteins are made inside mitochondria and are coded for by mitochondrial DNA. In plants, chloroplasts also make some cell proteins.
Extracellular and cell surface proteins destined to be degraded can move back into intracellular compartments upon being incorporated into endocytosed vesicles, some of which fuse with lysosomes where the proteins are broken down to their individual amino acids. The degradation of some membrane proteins begins while still at the cell surface when they are separated by secretases. Proteins that function in the cytoplasm are often degraded by proteasomes.
Cells may be observed under the microscope, using several different techniques; these include optical microscopy, transmission electron microscopy, scanning electron microscopy, fluorescence microscopy, and confocal microscopy.
There are several different methods used in the study of cells:
Purification of cells and their parts Purification may be performed using the following methods:
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Animal cells are typical of the eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles. Unlike the eukaryotic cells of plants and fungi, animal cells do not have a cell wall. This feature was lost in the distant past by the single-celled organisms that gave rise to the kingdom Animalia. Most cells, both animal and plant, range in size between 1 and 100 micrometers and are thus visible only with the aid of a microscope.
The lack of a rigid cell wall allowed animals to develop a greater diversity of cell types, tissues, and organs. Specialized cells that formed nerves and musclestissues impossible for plants to evolvegave these organisms mobility. The ability to move about by the use of specialized muscle tissues is a hallmark of the animal world, though a few animals, primarily sponges, do not possess differentiated tissues. Notably, protozoans locomote, but it is only via nonmuscular means, in effect, using cilia, flagella, and pseudopodia.
The animal kingdom is unique among eukaryotic organisms because most animal tissues are bound together in an extracellular matrix by a triple helix of protein known as collagen. Plant and fungal cells are bound together in tissues or aggregations by other molecules, such as pectin. The fact that no other organisms utilize collagen in this manner is one of the indications that all animals arose from a common unicellular ancestor. Bones, shells, spicules, and other hardened structures are formed when the collagen-containing extracellular matrix between animal cells becomes calcified.
Animals are a large and incredibly diverse group of organisms. Making up about three-quarters of the species on Earth, they run the gamut from corals and jellyfish to ants, whales, elephants, and, of course, humans. Being mobile has given animals, which are capable of sensing and responding to their environment, the flexibility to adopt many different modes of feeding, defense, and reproduction. Unlike plants, however, animals are unable to manufacture their own food, and therefore, are always directly or indirectly dependent on plant life.
Most animal cells are diploid, meaning that their chromosomes exist in homologous pairs. Different chromosomal ploidies are also, however, known to occasionally occur. The proliferation of animal cells occurs in a variety of ways. In instances of sexual reproduction, the cellular process of meiosis is first necessary so that haploid daughter cells, or gametes, can be produced. Two haploid cells then fuse to form a diploid zygote, which develops into a new organism as its cells divide and multiply.
The earliest fossil evidence of animals dates from the Vendian Period (650 to 544 million years ago), with coelenterate-type creatures that left traces of their soft bodies in shallow-water sediments. The first mass extinction ended that period, but during the Cambrian Period which followed, an explosion of new forms began the evolutionary radiation that produced most of the major groups, or phyla, known today. Vertebrates (animals with backbones) are not known to have occurred until the early Ordovician Period (505 to 438 million years ago).
Cells were discovered in 1665 by British scientist Robert Hooke who first observed them in his crude (by today's standards) seventeenth century optical microscope. In fact, Hooke coined the term "cell", in a biological context, when he described the microscopic structure of cork like a tiny, bare room or monk's cell. Illustrated in Figure 2 are a pair of fibroblast deer skin cells that have been labeled with fluorescent probes and photographed in the microscope to reveal their internal structure. The nuclei are stained with a red probe, while the Golgi apparatus and microfilament actin network are stained green and blue, respectively. The microscope has been a fundamental tool in the field of cell biology and is often used to observe living cells in culture. Use the links below to obtain more detailed information about the various components that are found in animal cells.
Centrioles - Centrioles are self-replicating organelles made up of nine bundles of microtubules and are found only in animal cells. They appear to help in organizing cell division, but aren't essential to the process.
Cilia and Flagella - For single-celled eukaryotes, cilia and flagella are essential for the locomotion of individual organisms. In multicellular organisms, cilia function to move fluid or materials past an immobile cell as well as moving a cell or group of cells.
Endoplasmic Reticulum - The endoplasmic reticulum is a network of sacs that manufactures, processes, and transports chemical compounds for use inside and outside of the cell. It is connected to the double-layered nuclear envelope, providing a pipeline between the nucleus and the cytoplasm.
Endosomes and Endocytosis - Endosomes are membrane-bound vesicles, formed via a complex family of processes collectively known as endocytosis, and found in the cytoplasm of virtually every animal cell. The basic mechanism of endocytosis is the reverse of what occurs during exocytosis or cellular secretion. It involves the invagination (folding inward) of a cell's plasma membrane to surround macromolecules or other matter diffusing through the extracellular fluid.
Golgi Apparatus - The Golgi apparatus is the distribution and shipping department for the cell's chemical products. It modifies proteins and fats built in the endoplasmic reticulum and prepares them for export to the outside of the cell.
Intermediate Filaments - Intermediate filaments are a very broad class of fibrous proteins that play an important role as both structural and functional elements of the cytoskeleton. Ranging in size from 8 to 12 nanometers, intermediate filaments function as tension-bearing elements to help maintain cell shape and rigidity.
Lysosomes - The main function of these microbodies is digestion. Lysosomes break down cellular waste products and debris from outside the cell into simple compounds, which are transferred to the cytoplasm as new cell-building materials.
Microfilaments - Microfilaments are solid rods made of globular proteins called actin. These filaments are primarily structural in function and are an important component of the cytoskeleton.
Microtubules - These straight, hollow cylinders are found throughout the cytoplasm of all eukaryotic cells (prokaryotes don't have them) and carry out a variety of functions, ranging from transport to structural support.
Mitochondria - Mitochondria are oblong shaped organelles that are found in the cytoplasm of every eukaryotic cell. In the animal cell, they are the main power generators, converting oxygen and nutrients into energy.
Nucleus - The nucleus is a highly specialized organelle that serves as the information processing and administrative center of the cell. This organelle has two major functions: it stores the cell's hereditary material, or DNA, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).
Peroxisomes - Microbodies are a diverse group of organelles that are found in the cytoplasm, roughly spherical and bound by a single membrane. There are several types of microbodies but peroxisomes are the most common.
Plasma Membrane - All living cells have a plasma membrane that encloses their contents. In prokaryotes, the membrane is the inner layer of protection surrounded by a rigid cell wall. Eukaryotic animal cells have only the membrane to contain and protect their contents. These membranes also regulate the passage of molecules in and out of the cells.
Ribosomes - All living cells contain ribosomes, tiny organelles composed of approximately 60 percent RNA and 40 percent protein. In eukaryotes, ribosomes are made of four strands of RNA. In prokaryotes, they consist of three strands of RNA.
In addition the optical and electron microscope, scientists are able to use a number of other techniques to probe the mysteries of the animal cell. Cells can be disassembled by chemical methods and their individual organelles and macromolecules isolated for study. The process of cell fractionation enables the scientist to prepare specific components, the mitochondria for example, in large quantities for investigations of their composition and functions. Using this approach, cell biologists have been able to assign various functions to specific locations within the cell. However, the era of fluorescent proteins has brought microscopy to the forefront of biology by enabling scientists to target living cells with highly localized probes for studies that don't interfere with the delicate balance of life processes.
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