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as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word "cell" being used to describe the smallest unit of a living organism]] ed for Keratin (red) and DNA (green)]] The cell is the structural and functional unit of all known , are Unicellular (consist of a single cell). Other organisms, such as Human s, are Multicellular . (Humans have an estimated 100 trillion or 1014 cells; a typical cell size is 10 µm ; a typical cell mass is 1 Nanogram .) The largest known cell is an Ostrich Egg . In 1837 before the final cell theory was developed, a Czech Jan Evangelista Purkyňe observed small "granules" while looking at the plant tissue through a microscope. The Cell Theory , first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann , states that all organisms are composed of one or more cells. All cells come from preexisting cells. Vital functions of an organism occur within cells, and all 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 ''cellula'', meaning, a small room. The descriptive name for the smallest living biologial structure was chosen by Robert Hooke in a book he published in 1665 when he compared the Cork cells he saw through his microscope to the small rooms monks lived in."... 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 any Writer or Person, that had made any mention of them before this. . ." – Hooke describing his observations on a thin slice of cork. Robert Hooke PREAMBLE Each cell is at least somewhat self-contained and self-maintaining: it can take in Nutrient s, 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. s across]] All cells have several different abilities: The Universal Features of Cells on Earth in Chapter 1 of the Alberts textbook (reference #1, above).
Some Prokaryotic cells contain important internal membrane-bound compartments,1 but Eukaryotic cells have a highly specialized Endomembrane System characterized by regulated Traffic and Transport of Vesicles .A. Rose, S. J. Schraegle, E. A. Stahlberg and I. Meier (2005) "Coiled-coil protein composition of 22 proteomes--differences and common themes in subcellular infrastructure and traffic control" in ''BMC evolutionary biology'' Vulume 5 article 66. Rose ''et al.'' suggest that Coiled-coil alpha helical vesicle transport proteins are only found in eukaryotic organisms. ANATOMY OF CELLS There are two types of cells: eukaryotic and prokaryotic. Prokaryotic cells are usually singletons, while eukaryotic cells are usually found in multicellular organisms. Prokaryotic cells See Also: Prokaryote cell]] 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:
Eukaryotic cells (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) Centriole s]] 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 Cell 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:
SUBCELLULAR COMPONENTS All cells, whether Prokaryotic or Eukaryotic , have a Membrane that envelops the cell, separates its interior from its environment, regulates what moves in and out (selectively permeable), and maintains the Electric Potential Of The Cell . Inside the membrane, a Salt y Cytoplasm takes up most of the cell volume. All cells possess DNA , the hereditary material of Gene s, and RNA , containing the information necessary to Build various Protein s such as Enzyme s, the cell's primary machinery. There are also other kinds of Biomolecule s in cells. This article will list these primary components of the cell, then briefly describe their function. Cell membrane: A cell's defining boundary See Also: Cell membrane The cytoplasm of a cell is surrounded by a ''plasma membrane''. The plasma membrane in plants and prokaryotes is usually covered by a Cell Wall . This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a Double Layer Of Lipids ( Hydrophobic fat-like molecules) and Hydrophilic Phosphorus molecules. Hence, the layer is called a Phospholipid Bilayer . It may also be called a fluid mosaic membrane. Embedded within this membrane is a variety of Protein molecules that act as channels and pumps that move different molecules into and out of the cell. The membrane is said to be 'semi-permeable', in that it can either 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 signalling molecules such as Hormone s. Cytoskeleton: A cell's scaffold See Also: Cytoskeleton The cytoskeleton 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 Cytokinesis , the separation of daughter cells after Cell Division ; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of Microfilament s, Intermediate Filament s and Microtubule s. There is a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The prokaryotic cytoskeleton is less well-studied but is involved in the maintenance of cell shape, polarity and cytokinesis.2 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 (e.g., Retrovirus es) 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 DNA 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 Chromosome s inside a discrete nucleus, usually with additional genetic material in some organelles like Mitochondria and Chloroplasts (see Endosymbiotic Theory ). A human cell has genetic material in the nucleus (the Nuclear Genome ) and in the mitochondria (the Mitochondrial Genome ). In humans 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 See Also: 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 Organelle s, that are adapted and/or specialized for carrying out one or more vital functions. Membrane-bound organelles are found only in eukaryotes. |
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