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Protoplasm is the living content of a cell that is surrounded by a plasma membrane.[1] This term is not commonly used in modern cell biology. Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and polysaccharides. In eukaryotes the protoplasm surrounding the cell nucleus is known as the cytoplasm and that inside the nucleus as the nucleoplasm. In prokaryotes the material inside the plasma membrane is the bacterial cytoplasm, while in gram-negative bacteria the region outside the plasma membrane but inside the outer membrane is the periplasm.

Protoplasm is distinct from non-living cell components lumped under "ergastic substances" or inclusion bodies, although ergastic substances can occur in the protoplasm. In many plant cells most of the volume of the cell is not occupied by protoplasm, but by "tonoplast," a large water filled vacuole enclosed by a membrane. A protoplast is a plant or fungal cell that has had its cell wall removed.

History of the term

The word protoplasm comes from the Greek protos for first, and plasma for thing formed. It was first used in 1846 by Hugo von Mohl to describe the "tough, slimy, granular, semi-fluid" substance within plant cells, to distinguish this from the cell wall, cell nucleus and the cell sap within the vacuole.[2] Thomas Huxley later referred to it as the "physical basis of life" and considered that the property of life resulted from the distribution of molecules within this substance. Its composition, however, was mysterious and there was much controversy over what sort of substance it was.[3] Unsurprisingly, attempts to investigate the origin of life through the creation of synthetic "protoplasm" in the laboratory were not successful.[4]

The idea that protoplasm is divisible into a ground substance called "cytoplasm" and a structural body called the cell nucleus reflects the more primitive knowledge of cell structure that preceded the development of electron microscopy, when it seemed that cytoplasm was a homogeneous fluid and the existence of most sub-cellular compartments, or how cells maintain their shape, was unknown.[5] Today, it is known that the cell contents are structurally very complex and contain multiple organelles.

See also

References

  1. ^ Cammack, Richard; Teresa Atwood; Attwood, Teresa K.; Campbell, Peter Scott; Parish, Howard I.; Smith, Tony; Vella, Frank; Stirling, John (2006), Oxford dictionary of biochemistry and molecular biology, Oxford [Oxfordshire]: Oxford University Press, ISBN 0-19-852917-1  
  2. ^ Protoplasm Later J.E Purkinje coined the term for Cytoplasm + Nucleoplasm in animal cell. 1911 Edition of the Encyclopaedia Britannica
  3. ^ Harvey, E. N. (2004), "Some Physical Properties of Protoplasm", Journal of Applied Physics 9: 68, doi:10.1063/1.1710397, http://link.aip.org/link/?JAPIAU/9/68/1  
  4. ^ Lazcano, A.; Capone, S.; Walde, P.; Seebach, D.; Ishikawa, T.; Caputo, R. (2008), "What Is Life? A Brief Historical Overview", Chemistry & Biodiversity 5: 1, doi:10.1002/cbdv.200890001, http://doi.wiley.com/10.1002/cbdv.200890001  
  5. ^ Satir, P. (2005), "Tour of organelles through the electron microscope: A reprinting of Keith R. Porter's classic Harvey Lecture with a new introduction", The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology 287A: 1184–1204, doi:10.1002/ar.a.20222, http://www3.interscience.wiley.com/cgi-bin/fulltext/112138393/HTMLSTART  
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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

PROTOPLASM, the name given in modern biology to a substance composing, wholly or in part, all living cells, tissues or organisms of any kind, and hence regarded as the primary living substance, the physical and material basis of life. The term "protoplasma," from irpcirros, first, and irXiivµa, formed substance, was coined by the botanist Hugo von Mohl, in 1846, for the "tough, slimy, granular, semi-fluid" constituent of plant cells, which he distinguished from the cellwall, nucleus and cell-sap. This was not, however, the first recognition of the true living substance as such, since this step had been achieved in 1835 by the French naturalist F. Dujardin, who in his studies on Foraminifera had proposed the term "sarcode" for the living material of their bodies in the following words: "Je propose de nommer ainsi ce que d'autres observateurs ont appele une gelee vivante, cette substance glutineuse, diaphane, insoluble dans l'eau, se contractant en masses globuleuses, s'attachant aux aiguilles de dissection, et se laissant etirer comme du mucus, enfin se trouvant dans tous les animaux inferieurs interposee aux autres elements de structure." To the French naturalist belongs, therefore, the real credit of the discovery of protoplasm, or rather, to be more accurate, of the first recognition of its true nature as the material basis of vital phenomena. Neither Dujardin nor von Mohl, however, had any conception of the universal occurrence and fundamental similarity of protoplasm in all living things, whether animal or vegetable, and it was not till 1861 that the identity of animal sarcode and vegetable protoplasm was proclaimed by Max Schultze, whose name stands out as the framer, if not the founder, of the modern notions concerning the nature of the living substance. From this time onwards the term "protoplasm" was used for the living substance of all classes of organisms, although it would have been more in accordance with the custom of priority in nomenclature to have made use of Dujardin's term "sarcode." A living organism, of any kind whatsoever, may be regarded as composed of (I) protoplasm, (2) substances or structures produced by the protoplasm, either by differentiation or modification of the protoplasm itself, or by the excretory or secretory activity of the living substance. The protoplasm of a given organism may be in a single individual mass, or may be aggregated into a number of masses or units, discontinuous but not disconnected, termed cells (see Cytology). Thus living organisms may be distinguished, in a general way, as unicellular or multicellular. An instance of a unicellular organism is well seen in an Amoeba, or in one of the Foraminifera, classic examples for the study of undifferentiated protoplasm, which here composes the greater part of the body, while products of the formative activity of the protoplasm are seen in the external shell and in various internal granules and structures. As an example of a multicellular organism we may take the human body, built up of an immense number of living cells which produce, singly or in co-operation, a variety of substances and structures, each contributing to the functions of the body. This, without attempting to enter into details, the horny epidermis covering the body, the hairs, nails, teeth, skeleton, connective tissue, &c., are all of them products formed by the metabolic activity of the living substance and existing in intimate connexion with it, though not themselves to be regarded as living. In addition to metabolic products of this kind, special modifications of the living substance itself are connected with specializations or exaggerations, as it were, of a particular vital function; such are the contractile substance of muscular tissue, and the various mechanisms seen in nervous and sensory tissue. It is necessary, therefore, in a living body of any kind, to distinguish clearly between simple protoplasm, its differentiations and its products.

Protoplasm from whatever source, whether studied in a cell of the human body, in an Amoeba or Foraminifer, or in a vegetable organism, is essentially uniform and similar in appearance and properties. Its appearance, graphically described by Dujardin in the passage quoted above, is that of a greyish, viscid, slimy, semi-transparent and semi-fluid substance. Its properties are those of living things generally, and the most salient and obvious manifestation of life is the power of automatic movement exhibited by living protoplasm. When free and not limited by firm envelopes, the movements take the character known generally as amoeboid, well shown in the common Amoeba or in the white corpuscles of the blood. When confined by rigid envelopes, as in plant-cells, the protoplasm exhibits streaming movements of various kinds. Even more essentially characteristic of the living matter than the power of movement is the property of metabolism - that is to say, the capacity of assimilating substances different from itself, of building them up into its own substance (anabolism), and of again decomposing these complex molecules into simpler ones (katabolism) with production of energy in the form of heat, movement and electrical phenomena. An important part of the metabolic process is respiration, i.e. the absorption of oxygen from the surrounding medium and oxidation of carbon atoms to form carbonic acid gas and other simple chemical compounds; in ordinary plant and animal protoplasm the process of respiration seems to be of universal occurrence, but some Bacteria constitute apparently an exception to the rule. Metabolism results not only in the generation of energy, but also, if anabolism be in excess of katabolism, in increase of bulk, and consequent growth and reproduction.

Living protoplasm is, therefore, considered from a chemical standpoint, in a state of continual flux and instability, and it follows that if protoplasm be a definite chemical substance or mixture of substances (see below), a given sample of protoplasm cannot be pure, or at least cannot remain so for any length of time so long as its power of metabolism is being exerted, but will contain particles either about to be built up by anabolism into its substance, or resulting from katabolic disintegration of its complex molecules. Hence it is convenient to distinguish the living substance from its metaplastic products of anabolism and katabolism. Such products are to be recognized invariably in protoplasm and take the form generally of granules and vacuoles. Granules vary in size from very minute to relatively large, coarse grains of matter, usually of a firm and solid nature. To the presence of innumerable granules is due the greyish, semi-transparent appearance of protoplasm, which in parts free from granules appears hyaline and transparent. Different samples of protoplasm may vary greatly in the number and coarseness of the granulations. Vacuoles are fluid drops of more watery consistence, which, when relatively small, assume a spherical form, as the result of surface tension acting upon a drop of fluid suspended in another fluid. When vacuoles are numerous and large, however, they may assume various forms from mutual pressure, like air-bubbles in a foam. A good example of frothy protoplasm, due to the presence of numerous vacuoles, is seen in the common "sun-animalcule" (Actinosphaerium). Or when the cell is confined by an envelope, and becomes very vacuolated, the vacuoles may become confluent to form a cellsap contained in a protoplasmic lining or "primordial utricle," and traversed by strands of protoplasm, as in the ordinary cells of plant-tissues. In many unicellular organisms, so-called contractile vacuoles are continually being formed as an act of excretion and expelled from the body when they reach a certain size.

While the majority of protoplasmic granules are probably to be regarded as metaplastic in nature, there is one class of granulations of which this is certainly not true, namely the grains of chromatin, so named from their peculiar affinity for certain dyes, such as carmine, logwood and various aniline stains. These grains may occur as chromidia, scattered through the protoplasm, or they may be concentrated at one or more spots to form a definite nucleus or nuclei, which may or may not be limited from the remaining protoplasm by a definite membrane, and may undergo further differentiations of structure which cannot be considered further here (see Cytology). The protoplasm of an ordinary cell is thus specialized into nucleus and cytoplasm. It was formerly thought that the most primitive forms of life, the Monera of E. Haeckel, consisted of pure protoplasm without a nucleus. It must be borne in mind, however, that chromatin can be present without being concentrated to form a definite nucleus, and that with imperfect technique the chromatin may easily escape observation. It seems justifiable at present to believe, until the contrary has been proved, that all organisms, however primitive, contain chromatin in some form: first, because this substance has always been found when suitable methods for its detection have been employed; secondly, because it has been shown experimentally, by cutting up small organisms, such as Amoeba, that enucleated fragments of protoplasm are unable to maintain their continued existence as living bodies; and, thirdly, because modern research has shown the chromatin to be of very great, perhaps fundamental, importance in regulating the vital processes of the cell and so determining the specific characters of the organism, a property which enables the chromatin to act as the vehicle of heredity and to transmit the characters of parent to offspring. In the present state of our knowledge, therefore, the peculiar chromatin-granules must be regarded as an integral part, perhaps even the most essentially and primarily important portion, of the living substance. At the same time it must be borne in mind that the term "chromatin" does not denote a definite chemical substance, to be recognized universally by hard and fast chemical tests. The chromatin of different organisms or cells may behave quite differently in relation to stains or other reactions; and if it be true that it is the chromatin which determines the nature and activities of the cell, it follows that no two cells which differ from one another in any way can have their chromatin exactly similar. The conception of chromatin is one based upon its relations to the vital activities and life cycle, as a whole, of the organism or cell, and not upon any definable material, that is chemical and physical, properties.

The importance of protoplasm, as the physical and material basis of life, has caused it to be the subject in recent years of much minute and laborious research. It seems obvious that matter so peculiarly endowed must possess a complexity of structure and organization far exceeding that which at first sight meets the eye. Some biologists have attacked the problem of the ultimate constitution of protoplasm from a purely theoretical standpoint, and have framed hypotheses of an ultramicroscopic constitution sufficient, in their opinion, to explain, or at least to throw light upon, the vital activities of the living substance. Others, proceeding by more empirical methods, have attempted to lay bare the structure of protoplasm by means of the refinements of modern microscopical technique, or to solve the question of its constitution by means of chemical and physiological investigation. Hence a convenient distinction, not always easy, however, to maintain in practice, is drawn between speculative and empirical theories of protoplasm.

i. Speculative theories have come with the greatest frequency from those who have attempted to find a material explanation for the phenomena of heredity (q.v.). As instances may be mentioned more particularly the "gemmules" of Darwin, the "pangenes" of de Vries, the "plastidules" of Haeckel, and the "biophores" of Weismann. These theories have been ably brought together and discussed by Delage, who has included them all under the term "micromerism," since they agree in the assumption that the living substance contains, or consists of, a vast number of excessively minute particles - i. e. aggregates or combinations of molecules, which give to the protoplasm its specific properties and tendencies ("idioplasm" of Nageli). In other cases the assumption of invisible protoplasmic units has been inspired by a desire either to explain the general vital and assimilative powers of protoplasm, as, for example, the "micellae" of Nageli and the "plasomes" of Wiesner, or to elucidate the mechanism of some one function, such as the "inotagmas" cf Engelmann, assumed to be the agents of contractility. In general, it may be said of all these speculations either that they can only be extended to all vital phenomena by the help of so many subordinate hypotheses and assumptions that they become unworkable and unintelligible, or that they only carry the difficulties a step further back, and really explain nothing. Thus it is postulated for Wiesner's hypothetical plasomes that they possess the power of assimilation, growth and reproduction by division; in other words, that they are endowed with just those properties which constitute the unexplained mystery of living matter.

2. Empirical theories of protoplasm differ according as their authors seek to find one universal type of structure or constitution common to all conditions or differentiations of the living substance, or, on the contrary, are of opinion that it may vary fundamentally in different places or at different times. From these two points of view protoplasm may be regarded either as monomorphic or polymorphic (Fischer). The microscopical investigation of protoplasm reveals at the first glance a viscid, slimy or mucilaginous substance, in which is embedded an immense number of granules, for the most part very tiny. Very rarely are these granules absent, and then only from a portion of the protoplasm, and only temporarily. Hence many authorities have regarded the minute granules - the "microsomes" of Hanstein - as themselves the ultimate living units of protoplasm, in opposition to those who would regard them merely as "metaplastic" substances, i.e. as the heterogeneous byproducts of metabolism and vital activity. The granular theory, as this conception of the living substance is called, has received its extreme elaboration at the hands of Altmann, whose standpoint may be taken as typical of this class of theories. After demonstrating the universal occurrence of granules in protoplasm, Altmann has compared each individual granule to a free-living bacterium, and thus regards a cell as a colony of minute organisms, namely the granules or bioblasts, as he has termed them, living embedded in a common matrix, like a zoogloea colony of bacteria. Of this theory it may be remarked, firstly, that it brings us no nearer to an explanation of vital phenomena than do the plasomes of Wiesner; secondly, that to consider bacteria as equivalent, not to cells, but to cell granules, is to assume for this class of organisms a position with regard to the cell theory which is, to say the least, doubtful; and, thirdly, that the observations of the vast majority of competent microscopists furnish abundant support for the statement that granules of protoplasm do not lie free in a structureless matrix, but are embedded in the substance of a minute and delicate framework or morphoplasm, which in its turn is bathed by a watery fluid or enchylema permeating the whole substance. The upholders of the granular theory deny the existence of the framework, or explain it as due to an arrangement of the granules, or as an optical effect produced by the matrix between the granules. Amongst those, on the other hand, who assert the existence of a framework distinct from granules and enchylema, the utmost diversity of opinion prevails with regard to the true structural relations of these three parts and the role played by each in the exercise of vital functions. Some have regarded the framework as made up of a tangle of separate fibrillae (filar theory) - a view more especially connected with the name of Flemming - but most are agreed that it represents the appearance of a reticulum or network with excessively fine meshes, usually from 2 to r ,u in diameter. The reticulum carries the granules at its nodal points, and is bathed everywhere by the enchylema. Even with so much in common, however, opinions are still greatly at variance. In the first place, the majority of observers interpret the reticulum as the expression of an actual spongy framework, a network of minute fibrillae ramifying in all planes. While, however, Heitzmann, following the speculations of Briicke, considered the framework itself to be actively contractile and the seat of all protoplasmic movement, an opposite point of view is represented by the writings of Leydig, Schafer and others, who regard the reticulum merely as a kind of supporting framework or spongioplasm, in which is lodged the enchylema or hyaloplasm, considered to be itself the primary motile and living substance. Biitschli, on the other hand, has pointed out the grave difficulties that attend the interpretation of the reticulum as a fibrillar framework, in view of the distinctly fluid consistence of, at any rate, most samples of protoplasm. For if the substance of the framework be assumed to be of a firm, solid nature, then the protoplasm as a whole could not behave as a fluid, any more than could a sponge soaked in water. On the other hand, the hypothesis of a fluid fibrillar framework leads to a physical impossibility, since one liquid cannot be permanently suspended in another in the form of a network. Biitschli therefore interprets the universally present reticulum as a meshwork of minute lamellae, forming a honeycombed or alveolar structure, similar to the arrangement of fluid lamellae in a fine foam or lather, in which the interstices are filled, not with air but with another fluid; in other words, the structure of protoplasm is that of an exceedingly fine emulsion of two liquids not miscible with one another.

It may be claimed for the alveolar theory of Biitschli that it throws light upon many known facts relating to protoplasm. It interprets the reticulum as the optical section of a minute foam-like structure, and permits the formation of protoplasmic striations and of apparent fibrillae as the result of linear or radiating dispositions of the alveolar framework; it reconciles with the laws of physics the combination of a framework with a fluid or semi-fluid aggregate condition, while variations in the fluidity of the framework are compatible with a stiffening of the protoplasm almost to the pitch of rigidity, as seen, for example, in nervous tissue; and, finally, it explains many characteristic structural peculiarities of protoplasm, such as the superficial layer of radiately arranged alveoli, the spherical form of vacuoles, the continuous wall or pellicle which limits both the vacuoles and the protoplasm as a whole, and many other points not intelligible on the theory of a sponge-like structure. Bi tschli has succeeded, moreover, in producing artificial foams of minute structure, which not only mimic the appearance of protoplasm, but can be made to exhibit streaming and amoeboid movements very similar to those of simple protoplasmic organisms. Incidentally these experiments have shown that many of the apparent granulations and "microsomes" are an optical effect produced by the nodes of the minute framework. In his most recent works Biitschli has extended his theory of alveolar structure to many other substances, and has tried to prove that it is a universal characteristic of colloid bodies, a view strongly combated, however, by Fischer. While it cannot be claimed that Biitschli's theory furnishes in any way a complete explanation of life, leaving untouched, as it does, the fundamental question of assimilation and metabolism, he at least draws attention to a very important class of facts, which, if demonstrated to be of universal occurrence, must be reckoned with in future treatment of the protoplasm question, and would form an indispensable preliminary to all speculations upon the mechanism of the living substance.

In opposition to the above-mentioned monomorphic theories of protoplasm, all of which agree in assuming the existence of some fundamental type of structure in all living substance, attempts have been made at various times to show that the structural appearances seen in protoplasm are in reality artificial products, due to precipitation or coagulation caused by reagents used in the study or preparation of living objects. These views have been developed by Fischer, who by experimenting upon various proteids with histological fixatives, has shown that it is possible to produce in them a granular, reticular or alveolar structure, according to treatment, and, further, that granules so produced may be differentially stained according to their size and absorptive powers. Fischer therefore suggests that many structural appearances seen in protoplasm may be purely artificial, but does not extend this view to all such structures, which would indeed be impossible, in view of the frequency with which reticular or alveolar structures have been observed during life. He suggests, however, that such structures may be temporary results of vital precipitation of proteids within the organism, and that protoplasm may have at different times a granular reticular or alveolar structure, or may be homogeneous. Fischer's conception of living protoplasm is therefore that of a polymorphic substance, and a similar view is held at the present time by Flemming, Wilson and others. Strassburger also regards protoplasm as composed of two portions: a motile kinoplasm which is fibrillar, and a nutritive trophoplasm which is alveolar, in structure.

The chemical investigation of protoplasm labours at the outset under the disadvantage that it cannot deal with the living substance as a whole, since no analysis can be performed upon it without destroying the life. Protoplasm consists, to the extent of about 60% of its total mass, of a mixture of various nucleo-proteids - that is to say, of those substances which, in molecular structure 4nd chemical composition, are the most complex bodies known. In association with them are always found varying amounts of fats, carbohydrates, and other bodies, and such compounds are always present in the living substance to a greater or less degree as products of both upward and downward metabolism. Protoplasm also contains a large but variable percentage of water, the amount of which present in any given case affects largely its fluid or viscid aggregate condition. Especial interest attaches to the remarkable class of bodies known as ferments or enzymes, which when prepared and isolated from the living body are capable of effecting in other substances chemical changes of a kind regarded as specifically vital. It is from their study, and from that of the complex proteids found in the living body, that the greatest advances towards an explanation of the properties of living matter may be expected at the present time.

The question may be raised how far it is probable that there is one universal living substance which could conceivably be isolated or prepared in a pure state, and which would then exhibit the phenomena characteristic of vital activity. It is sufficiently obvious, in the first place, that protoplasm, as we know it, exhibits infinite diversity of character, and that no two samples of protoplasm are absolutely similar in all respects. Chemical differences must be assumed to exist not only between the vital fabrics of allied species of organisms, but even between those of individuals of the same species. Kassowitz regards this variability as compatible with the assumption of a gigantic protoplasmic molecule in which endless variations arise by changes in the combinations of a vast number of atoms and atom complexes. It is difficult to conceive, however, of any single substance, however complex in its chemical constitution, which could perform all the functions of life. To postulate a universal living substance is to proceed along a path which leads inevitably to the assumption of biophores, plastidules or other similar units, since the ultimate living particles must then be imagined as endowed at the outset with many, if not all, of the fundamental properties and characteristic actions of living bodies. Such a conception has as its logical result a vitalistic standpoint, which may or may not embody the correct mental attitude with regard to the study of life, but which at any rate tends to check any further advance towards an explanation or analysis of elementary vital phenomena. We may rather, with Kolliker, Verworn and others, ascribe the activities of protoplasm to the mutual interaction of many substances, no single one of which can be considered as living in itself, but only in so far as it forms an indispensable constituent of a living body. From this point of view life is to be regarded, not as the property of a single definite substance, but as the expression of the ever-changing relations existing between the many substances which make up the complex and variable congeries known to us as protoplasm.

Authorities

- For exhaustive historical summaries of the protoplasm question, with full bibliographical references, the reader may be referred to the following works, especially the first five: Biitschli, Investigations on Microscopic Foams and Protoplasm (London, 1894) Untersuchungen fiber Strukturen (Leipzig, 1898); "Meine Ansicht fiber die Struktur des Protoplasmas and einige ihrer Kritiker," Arch. f. Entwickelungsmechanik d. Org. (1901); xi. 499-584, pl. xx.; Delage, La Structure du protoplasme et les theories sur l heredite (Paris, 1895); Wilson, The Cell (2nd ed., London, two); Fischer, Fixirung, Fdrbung, and Bau des Protoplasmas (Leipzig, 1899); Kassowitz, Allgemeine Biologie (Vienna, 1899); G. Mann, Protoplasm, its Definition, Chemistry and Structure (Oxford, 1906), p. 59.

(E. A. M.)


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Wikibooks

Up to date as of January 23, 2010
(Redirected to Cell Biology/Glossary article)

From Wikibooks, the open-content textbooks collection

Alpha Helix
DNA forms a specific formation called a alpha helix.
Amino Acid
The basic subunit of proteins.
Atom
One unit of a given element.
Bacteria
Carbohydrate
Carbon
One of the common elements found in organic matter and living things.
Cell Wall
found in prokaryotic plants and it provides structural support and protection.
Chloroplasts
convert light/food into usable energy. (ATP production)
Cholesterol
Found in cell membranes, affects the rigidity of the membrane. Also a basic compound used to form man hormones.
Chromatin
Chromosome
A group of genes/DNA that are contiguous, a functional unit. Humans have 23 pairs chromosomes.
Cilia
Hair-like structures.
Cisternae
The flatten sacs of the Rough Endoplasmic Reticulum.
Crossover
Genetics term for chromosomes literally crossing over DNA from one chromosome to another.
Cyanophytes
One type of prokaryote (cell without a nucleus).
Cytoplasm
the protoplasm outside the nucleus
Cytoskeleton
Microtubules, actin and intermediate filaments. This produces the support structure/shape of cells. Of course plant cells have a much more rigid shape due to the cell wall.
Cytosol
The 'fluid' portion of the cell, it is made up of water and many free proteins and other elements - all except the organelles.
DNA
Deoxyribonucleic Acid, made up of 4 nucleotides: Adenine, Guanine, Thymine, and Cytosine (A,G,T,C).
Element
Element is one atom of a particular substance found on the periodic table. (Things such as Carbon, Hydrogen, Oxygen, etc.)
Endoplasmic Reticulum (ER)
Important for protein synthesis. It is a transport network for molecules destined for specific modifications and locations. There are two types: Rough ER - has ribosomes, and tends to be more in 'sheets'. Smooth ER - Does not have ribosomes and tends to be more of a tubular network.
Eukaryote
A Cell with a nucleus.
Flagella
Gene
Genetic Material
Globular Protein
Glycolipids
Glycoprotiens
Golgi Apparatus
important for glycosylation, secretion.
Histones
Hydrogen
A common element in organic and living organisms.
Hydrophilic
'likes water' (hydro = water; philic = like). Meaning that a hydrophilic molecule or portion would be attracted to water. Much like the opposite poles of a magnet pulling each other together.
Hydrophobic
'fears water' (hydro = water; phobic = fear). Meaning that a hydrophobic molecule or portion would be repulsed/push-away a water molecule. This would be like trying to put together the same pole of two magnets. Examples: oils, fatty acids (i.e. the 'tails' of phospholipids), cholesterol.
Lipid
Lysosomes
Digestive sacks - the main point of digestion, these are only found in animal cells.
Meiosis
is a type of cell division. See section on meiosis. This occurs for formation of egg/sperm cells, which in the end have 1/2 the normal number of chromosomes, only 1 copy of each chromosome.
Micrometer
A unit of measure in the metric system. 10^-6 meters.
Microtubules
made from tubulin, and make up centrioles,cilia,etc.
Millimeter
A unit of measure in the metric system. 10^-3 meters.
Mitochondria
convert foods into usable energy. (ATP production) A mitochondrion does this through aerobic respiration. They have 2 membranes, the inner membranes shapes differ between different types of cells, but they form projections called cristae. The mitochondrion is about the size of a bacteria, and it carries its own genetic material and ribosomes.
Mitosis
The cell division, that is found in most non-reproductive cells.
Nanometer
A unit of measure in the metric system. 10^-9 meters.
Nitrogen
A common element in organic and living organisms.
Nucleic Acid
Basic Building block for DNA.
Nucleolus
Or densely packed portion of the Nucleus.
Nucleus
(only in eukaryotes) - where genetic material (DNA) is located, RNA is transcribed.
Organelles
(which also have membranes) in 'higher' eukaryote organisms:
Osmosis
Oxygen
A common element in organic and living organisms.
Peptidoglycan
This is the main component of prokaryotic cell walls, it is made from a large protein polymer and sugar.
Peroxisomes
Use oxygen to carry out catabolic reactions, in both plant and animals.
Phospholipid
See the section of the course on Cell Membranes and specifically phospholipids.
Phosphorus
A common element in organic and living organisms.
Plasma membrane
The surface around the cell made up of phospholipids, proteins, cholesterol, etc.. See the section on the Cell Membrane
Plasmid
Plastids
Prokaryote
Cells without a nucleus.
Protein
Protoplasm
the living material in the cell
Pseudopod
literally means 'False foot'
RNA
Ribonucleic Acid
RNApolymerase
Recombination
Ribosomes
half are on the Endoplasmic Reticulum, the other half are 'free' in the cytosol, this is where the RNA goes for translation into proteins.
Sulphur
A common element in organic and living organisms.
Vacuole
Vesicle
tRNA
Transfer RNA, cool 3D structure. It works with the ribosome and mRNA to form proteins (called translation). It has a 'anti-codon' which will match codons of the mRNA, and also has a amino-acid. The tRNA is a key to the having the Amino-acid match a specific codon on the mRNA, See the Codon Table to see how these are matched in general. Please NOTE: There are differences in how the matches take place in mitochondria and bacteria.

Simple English

Protoplasm is the living substance that make up a cell. In plant cells, it is surrounded by a cell wall. In animal cell, the whole cell is made of protoplasm, surrounded by a cell membrane. Protoplasm in living beings is made up of about 75-80 percent water.



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