Chapter 6 Vocabulary
nucleoid
nucleoid is a region where the cell's DNA is located and is not enclosed by a membrane. Instead of having a nucleus, prokaryotic cells have nucleoids.
plastid
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primary cell wall
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pseudopodium
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Microfilament-
A solid od of actin protein in the cytoplasm of almost all eukaryotic cells, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction. or actin filaments are the thinnest filaments of the cytoskeleton, a structure found in the cytoplasm of eukaryotic cells. These linear polymers of actin subunits are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fractureby nanonewton tensile forces. Microfilaments are highly versatile, functioning in cytokinesis, amoeboid movement, and changes in cell shape. In inducing this cell motility, one end of the actin filament elongates while the other end contracts, presumably by myosin II molecular motors.[1]Additionally, they function as part of actomyosin-driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's ATP-dependent pulling action in muscle contraction and pseudopod advancement. Microfilaments have a tough, flexible framework which helps the cell in movement.
Intermediate filament-
A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments. cytoskeletal components found in metazoan cells. They are composed of a family of related proteinssharing common structural and sequence features. Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin (microfilaments), and that of 25 nm microtubules, although they were initially designated 'intermediate' because their average diameter is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells.[1][2] Most types of intermediate filaments are cytoplasmic, but one type, the lamins, are nuclear.
Food Vacuole
A food vacuole is a membranous sac formed by phagocytosis. A plant or fungal cell may have one or several vacuoles. Phagocytosis is a process used by cells to engulf and subsequently ingest particles of nutrients or bacteria. This process is a very important part of cell function, allowing cells to grab vital nutrients and allowing the body to protect itself from harmful bacteria. A cell that specializes in this process is known as a phagocyte. In this process, a cell deforms its membrane to form a little cone around the piece of material that is to be absorbed, and then it closes the sides of the cone, hugging the particle in the cell membrane to create what is known as a phagosome or food vacuole, like a little envelope of material surrounded by the cell membrane.
lysosome
A lysosome is a structure inside an animal cell which breaks down materials into compounds which can be used or discarded by the cell, as needed. Lysosomes also play other important roles in cell upkeep, ranging from consuming worn-out structures within the cell to attacking foreign bacteria before it has a chance to penetrate the cells. With a powerful microscope, it is possible to see lysosomes within the cell; these structures are typically spherical in shape. Each cell contains a multitude of lysosomes, and each lysosome produces an assortment of digestive enzymes which it uses to break down food and waste material. Because a lysosome needs an acidic environment to function properly, these organelles are encompassed in a membrane to ensure that they stay acidic; to digest things, a lysosome engulfs them, treats them with an appropriate enzyme, and then spits the results of the digestion back out for the cell to use.
peroxisome
A peroxisome is a specialized structure inside a cell which helps to rid the body of the host organism of toxins. In animals, peroxisomes are often especially concentrated in the neighborhood of the liver and kidneys, the filtration centers for toxins. In plants, peroxisomes assist with photosynthesis. In either instance, a peroxisome disorder can be a serious problem, as these structures are crucial to the wellbeing of much of life on Earth.
nucleolus
A prominent structure within the non-dividing nucleus is the nucleolus, which appears through the electron microscope as a mass of densely stained granules and fibers adjoining part of the chromatin. here a special type of RNA called robosomal RNA (rRNA) is synthesized from instructions in the DNA. also, proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits in the nucleolus. these subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and small subunit can assemble into a ribosome. sometimes there are two or more nucleoli; the number depends of the species and the stage in the cell's reproductive cycle. recent studies have suggested that the nucleolus may perform additional functions as well.
integrin-
A receptor protein built into the plasma membrane that interconnects the cellular matrix and the cytoskeleton. transmembrane receptors that mediate the attachment between a cell and its surroundings, such as other cells or the extracellular matrix (ECM). In signal transduction, integrins pass information about the chemical composition and mechanical status of the ECM into the cell. Therefore, in addition to transmitting mechanical forces across otherwise vulnerable membranes, they are involved in cell signaling and the regulation of cell cycle, shape, and motility.Typically, receptors inform a cell of the molecules in its environment and the cell responds. Not only do integrins perform this outside-in signaling, but they also operate an inside-out mode. Thus, they transduce information from the ECM to the cell as well as reveal the status of the cell to the outside, allowing rapid and flexible responses to changes in the environment, for example to allow blood coagulation by platelets.
Granum-
A stacked portion of the thylakoid membrane in the chloroplast, Grana function in the light reactions of photosynthesis.
middle lamella-
A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells. a pectin layer which cements the cell walls of two adjoining cells together. Plants need this to give them stability and so that they can form plasmodesmata between the cells. It is the first formed layer which is deposited at the time of cytokinesis. The cell plate that is formed during cell division itself develops into middle lamella or lamellum. The middle lamella is made up of calcium and magnesium pectates.[1]In plants, the pectins form an unified and continuous layer between adjacent cells. Frequently, it is difficult to distinguish the middle lamella from the primary wall, especially in cells that develop thick secondary walls. In such cases, the two adjacent primary walls and the middle lamella, and perhaps the first layer of the secondary wall of each cell, may be called a compound middle lamella. In multicelluar organisms, when middle lamella dissolves, the cells get isolated from each other. If enzymes degrade the middle lamella, the adjacent cells will separate.
Eukaryotic cell-
A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, organisms with Eukaryotic cells (protists, plants, fungi, and animals) are called Eukaryotes.
Vesicle
A vesicle can be visualised as a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes or they may be prepared. Artificially prepared vesicles are known as liposomes. Most vesicles have specialized functions depending on what materials they contain. Vesicles store, transport, or digest cellular products and waste. The membrane enclosing the vesicle is similar to that of the plasma membrane, and vesicles can fuse with the plasma membrane to release their contents outside of the cell. Vesicles can also fuse with other organelles within the cell.
Actin
Actin is a protein that functions in the contractile system of skeletal muscle, where it is found in the thin filaments. In muscle, fibrous actin (F-actin) is a helical polymer of a globular polypeptide chain, G-actin. Actin is present in all eukaryotes and has a highly conserved protein sequence. Actins of non-muscle cells are encoded by different genes than those of muscle, and have been found to be involved in platelet shape, endocytosis, cell motility, cell division, cell division, and cell signaling.
Cytosol
All cells have several basic functions in common: they are all bounded by a membrane, called a plasma membrane. within the membrane is a semi fluid substance, cytosol, in which organelles are found. Cytosol is found in both eukaryotic and prokaryotic cells.
organelle
Although cells were discovered by Robert Hooke in 1665, the geography of the cell was largely uncharted until the 1950s. Most subcellular structures, or organelles, are too small to be resolved by the light microscope. cell biology advanced rapidly in the 1950s with the introduction of the electron microscope. resolution is in these microscopes allowed people to see the organelles in cells unlike the light microscope.
rough ER
An endoplasmic reticulum (ER), a eukaryotic organelle made up of a system of membranous tubes and sacs, that is studded with ribosomes on its surface giving it a rough appearance under the microscope (hence its name). The ribosomes that give the endoplasmic reticulum a 'rough' appearance are not always bound with the ER. They bind to it when it starts to synthesize membrane-bound proteins destined for sorting.
Endoplasmic reticulum-
An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane. There is both rough ER that is studded with ribosomes and smooth ER that is not studded with ribosomes. the ER is extensive and has many folds, creating isolated areas of the ER that develop special conditions such as a specific pH to create a specialized environment for the synthesis of a specific molecule such as a protein.
plasma membrane
At the boundary of every cell, the plasma membrane functions as a selective barrier that allows sufficient passage of oxygen, nutrients, and wastes to service the entire volume of the cell. for each square micrometer of membrane, only so much of a particular substance can cross per second. rates of chemical exchange with the extracellular environment might be inadequate to maintain a cell with a very large cytoplasm. the need for a surface area sufficiently large to accommodate the volume helps explain the microscopic size of most cells. larger organisms do not generally have larger cells than smaller organism.
chloroplast
Chloroplasts are organelles only found in plants and algae and are the sites of photosynthesis. organisms transform energy they acquire from their surroundings. In eukaryotic cells, mitochondria and chloroplasts convert energy to forms that cells can use for work. chloroplasts convert solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water. it is not part of the endomembrane system. it has at least two membranes separating the innermost space from cytosole.
chromatin
Chromosomes are made up of a material called chromatin, a complex of proteins and DNA. as a cell prepares to divide, however, the thin chromatin fibers coil (condense), becoming thick enough to be distinguished as the familiar separate structures known as chromosomes. each eukaryotic species has a characteristic number of chromosomes. A typical human cell, for example, has 46 chromosomes in its nucleus; the exception are the sex cells (egg and sperm), which have only 23 chromosomes in humans. A fruit fly cell has 8 chromosomes in most cells, with 4 in the sex cells.
Desmosome
Desmosomes one of the tree main types of intercellular junctions. They are especially common in epithelial tissue, which lines the external and internal surfaces of the body. They function like rivets, fastening cells together into strong sheets. intermediate filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm.
Gap Junction
Gap junctions are a type of intercellular junction. it is especially common in epithelial tissue, which lines the external and internal surfaces of the body. Gap junctions provide cytoplasmic channels from one cell to an adjacent cell. gap junctions consist of special membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissues, including heart muscle, and in animal embryos.
Glycoproteins
Glycoproteins are proteins that have carbohydrates covalently bonded to them. most secretory proteins are glycoproteins. the carbohydrate is attached to the protein in the ER by specialized molecules built into the ER membrane. once secretory proteins are formed, the ER membrane keeps them separate from the proteins, produced by free ribosomes, that will remain in the cytosol. secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called the transitional ER.
Cillium
In eukaryotes, a specialized arrangement of microtubules is responsible for the beating of flagella and cilia, locomotor appendages that protrude from some cells. many unicellular eukaryotic organisms are propelled through water by cilia or flagella. when cilia extend from cells that are held in place as part of a tissue layer, they can move fluid over the surface of the tissue. for example, the ciliated lining of the windpipe sweeps mucus containing trapped debris out of the lungs. in a woman's reproductive tract, the cilia lining the oviducts (fallopian tubes) help move an egg toward the uterus. cilia works similar to oars, with alternating power and recovery strokes generating force in a direction perpendicular to the cilium's axis.
centrosome
In many cells, microtubules grow out from a centrosome, a region often located near the nucleus that is considered to be a "microtubule0organizing center." these microtubules function as compression resisting girders of the cytoskeleton. Within the centrosome of an animal cell are a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring.
Electron Microscope
Instead of using light, the electron microscope focuses a beam of electrons through the specimen or onto its service. resolution is inversely related to the wavelength of the radiation a microscope uses for imaging, and electron beams have a wavelength much shorter than the wavelengths of visible light. Modern electron microscopes can theoretically achieve a resolution of about .002 nm but the practical limit for biological structures is generally only about 2 nm - still a hundredfold improvement over the light microscope.
Endomembrane system
Many of the different membranes of the eukaryotic cell are part of an endomembrane system, which carries out a variety of tasks in the cell. these tasks include synthesis of proteins and their transport into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. the membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles. despite these relationships, the various membranes are not identical in structure and function. moreover, the thickness, molecular composition, and types of chemical reactions carried out by proteins in a given membrane are not fixed, but may be modifies several times during the membrane's life. the endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various kinds of vacuoles, and the plasma membrane.
central vacuole
Mature plant cells generally contain a large central vacuole enclosed by a membrane called the tonoplast. the central vacuole develops by the coalescence of smaller vacuoles, themselves derived from the endoplasmic reticulum and golgi apparatus. the vacuole is in this way an integral part of a plant cell's endomembrane system. like all cellular membranes, the tonoplast is selective in transporting solutes; as a result, the solution inside the vacuole, called cell sap, differs in composition from the cytosol. the plant cell's central vacuole is a versatile compartment. it can hold reserves of important organic compounds such as the proteins stockpiled in the vacuoles of storage in cells in seeds. it is also the plan cell's main repository of inorganic ions such as potassium and chloride. vacuoles may also help protect the plant against predators containing compounds that are poisonous or unpalatable to animals. the vacuoles play a major role in the growth of plant cells which enlarge as their vacuoles absorb water, enabling the cell to become larger with a minimal investment in new cytoplasm.
mitochondrion
Mitochondria are the power plants of animal and plant cells. They convert bloodborne NADH and NADPH into ATP (adenosine triphosphate), the common energy currency of cellular machinery. The singular of mitochondria is mitochondrion. It is strongly suspected that mitochondria derive from early symbiotic cells living in cooperation with other cells. These organelles have their own DNA, and evolution has already spent millions of years incrementally transferring DNA from the mitochondria to the nucleus of the cell, where the rest of the DNA resides.
plasmadesmata
Plant cell walls are perforated with channels called plasmamodesmata. cytosol passes through the plasmodesmata and connects the chemical environments of adjacent cells. these connections unify most of the plant into one living continuum. the plasma membranes of adjacent cells line the channels of each plasmodesma and thus are continuous. water and small solutes can pass freely from cell to cell, and recent experiments have shown that in certain circumstances, specific proteins and RNA molecules can also do this. the macromolecules to be transported to neighboring cells seem to reach the plasmadesmata by moving alon fibers of the cytoskeleton.
Cytoskeleton
Previously, it was thought that organelles of a eukaryotic cell floated freely in the cytosol. Inprovements in both light microscopy and electron microscopy have reaveled the cytoskeleton, a network of fibers extending throughout the cytoplasm. the cytoskeleton, which plays a major role in organizing the structures and activities of the cell, is composed of three types of molecular structures: microtubules, microfilaments, and intermediate filaments.
ribosome
Ribosomes, particles made of ribosomal RNA and protein, are organelles that carry out protein synthesis. cells that have high rates of protein synthesis have a particularly large number of ribosomes. for example, a human pancreas cell has a few million ribosomes. Ribosomes build proteins in two cytoplasmic locales. free ribosomes are suspended in the cytosol while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope. most of the proteins made of free ribosomes function within the cytosol; examples are enzymes that catalyze the first steps of sugar breakdown. bound ribosomes generally make proteins that are destined either for insertion info membranes, for packaging with certain organelles such as lysosomes or for export from the cell (secretion). cells that specialize in protein secretion - for instance, the cells of the pancreas that secrete digestive enzymes - frequently have a high proportion of bound ribosomes. bound a free ribosomes are structurally identical and can alternate between the two roles.
centriole
Within the centrosome of an animal cell are a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring. Before a cell divides, the centrioles replicate. although centrioles may help organize microtubule assembly, they are not essential for this function in all eukaryotes; centrosomes of most plants lack centrioles, but have well organized microtubules.
Golgi apparatus
The Golgi apparatus is an organelle that is present in most eukaryotic cells, which are cells that contain internal structures. It is commonly thought of as the cell's packaging and processing center. Cells produce many different molecules, such as lipids and proteins. After they are produced, they are sent to the Golgi apparatus where they are modified, packaged, and sent away. The Golgi apparatus is composed of stacks of membrane-bound structures known as cisternae. There are typically four to eight cisternae in each apparatus. Each single part of a cisternae, known as a cisterna, is a flattened membrane disc that contains enzymes used for modifying molecules. The whole structure is located between the endoplasmic reticulum, or the cell's "factory," and the cell membrane. The position and structure of the Golgi apparatus allows materials produced in the endoplasmic reticulum to be quickly processed and "shipped" out of the cell's membrane. The Golgi Apparatus plays an integral part in preparing molecules for use both inside and outside of the cell. Its primary purpose is the modification of proteins, which serve vital roles in nearly every biological process. It adds sugars and phosphate groups to proteins, modifying their structures and functions to match their specific tasks. Additionally, it is involved in the transportation of lipids and the production of lysosomes, which contain digestive enzymes that break down substances in cells.
cell wall
The cell was is an extracellular structure of plant cells that distinguishes them from animal cells. the wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. on the level of the whole plant, the strong walls of specialized cells hols the plant up against the force of gravity. Prokaryotes, fungi, and some protists also have cell walls.
tonoplast
The cytoplasmic membrane surrounding the vacuole, separating the vacuolar contents from the cytoplasm in a cell. As a membrane, it is mainly involved in regulating the movements of ions around the cell, and isolating materials that might be harmful or a threat to the cell.
Cytoplasm-
The entire contents of the cell, including organelles but exclusive of the nucleus. and bounded by the plasma membrane.
Cell Fractionation
The goal of cell fractionation is to take cells apart and separate the major organelles from one another. the instrument used to fractionate cells is the centrifuge, which can spin test tubes holding mixtures of disrupted cells at various speeds. the resulting force separates the cell components by size and density. Cell Fractionation enables the researcher to prepare specific components of cells in bulk by quantity to study their composition and functions. by following this approach, biologists have been able to assign various functions of the cell to different organelles, a task that would be far more difficult with intact cell. for example, one cellular fraction collected by centrifugation has enzymes that function in the metabolic process known as cellular respiration. the electron microscope reveals this fraction to be very rich in the organelles called mitochondria. this evidence helped cell biologists determine that mitochondria are the sites of cellular respiration.
light microscope
The microscopes first used by renaissance scientists, as well as in high school labs, are all light microscopes. Visible light is passed through the specimen and then through glass lenses. the lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye, onto photographic film or a digital sensor, or on a video screen.
Basal Body
The microtubule assembly of a cilium or flagellum is anchored in the cell by a basal body, which is structurally identical to a centriole. In fact, in many animals, including humans, the basal body of the fertilizing sperms flagellum enters the egg and becomes a centriole.
Collagen
The most abundant glycoprotein in the extracellular matrix (ECM) is collage, which forms strong fibers outside the cells. in fact, collagen accounts for about half of the total protein in the human body. the collagen fibers are embedded in a network woven from proteoglycans which are glycoproteins of another class.
nuclear envelope
The nuclear envelop encloses the nucleus, separating its contents from the cytoplasm. the nuclear envelope is a double membrane. the two membranes, each a lipid bilayer with associated proteins, are separated by a space of 20-40 nm. the envelope is perforated by pores that are about 100 nm in diameter. at the lip of each pore, the inner and outer membranes of the nuclear envelope are continuous. an intricate protein structure called a pore complex lines each pore and regulates the entry and exit of certain large macromolecules and particles. except for the pores, the nuclear side of the envelope is lined by the nuclear lamina, a net like array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelop.
Scanning Electron microscope (SEM)
The scanning electron microscope is a type of electron microscope. it is especially useful for detailed study of the surface of a specimen. the electron beam scans the surface of the sample, which is usually coated with a thin film of gold. the bean excites electrons on the sample's surface, and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen. the result is an image of the topography of the specimen. the SEM has great depth of field, which results in an age that appears three dimensional.
extracellular matrix (ECM)-
The substance in which animal tissues are embedded, consisting of proteins and polysaccharides.
prokaryotic cell
The work prokaryotic is from the Greek pro meaning before and karyon meaning kernel, referring here to the nucleus. In a prokaryotic cell, the DNA is concentrated in a region called the nucleoid, but no membrane separates this region from the rest of the cell. Prokaryotic cells, like eukaryotic cells, have a plasma membrane called cytoplasm, however prokaryotic cells to not have membrane bound organelles suspended in cytosol.
smooth ER
There are two distinct, though connected regions of ER that differ in structure and function: smooth ER and rough ER. smooth ER is so named because its outer surface lacks ribosomes. The smooth ER of various cell types function in diverse metabolic processes. these processes include synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. It is seen connected to the nuclear envelope, and consists of tubules and vesicles that branch forming a network to increase surface area for the action or storage of key enzymes. It contains the enzyme Glucose-6-phosphatase (which converts glucose-6-phosphate to glucose), a step in gluconeogenesis. A specialized form of SER (called sarcoplasmic reticulum) occurs in muscle cells where calcium ions are stored. It is also abundant in hepatocytes to process and detoxify lipophilic drugs
myosin
Thousands of actin filaments are arranged parallel to one another along the length of a muscle cell, integrated with thicker filaments made of a protein called myosin. myosin acts as a motor protein by means of projections (arms) that "walk" along the actin filaments. contraction of the muscle cell results from the actin and myosin filaments sliding past one another in this way, shortening the cell. in other kinds of cells, actin filaments are associated with myosin in miniature and less elaborate versions of the arrangement in muscle cells. these actin-myosin aggregates are responsible for localized contractions of cells. for example, a contracting belt of microfilaments forms a cleavage furrow that pinches a dividing animal cell into two daughter cells.
tight junction
Tight junctions are a type of intercellular junction. it is especially common in epithelial tissue, which lines the external and internal surfaces of the body. At tight junctions, the membranes o neighboring cells are very tightly pressed against each other, bound together by specific proteins. forming continuous seals around the cells, tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells.
chromosome
Within the nucleus, the DNA is organized into discrete unites called chromosomes, structures that carry the genetic information. Chromosomes are made up of a material called chromatin, a complex of proteins and DNA. as a cell prepares to divide, however, the thin chromatin fibers coil (condense), becoming thick enough to be distinguished as the familiar separate structures known as chromosomes. each eukaryotic species has a characteristic number of chromosomes. A typical human cell, for example, has 46 chromosomes in its nucleus; the exception are the sex cells (egg and sperm), which have only 23 chromosomes in humans. A fruit fly cell has 8 chromosomes in most cells, with 4 in the sex cells.
microtubule-
a hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytokeleton.a component of the cytoskeleton, found throughout the cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres, with an average length of 25 µm and are highly dynamic. The outer diameter of a microtubule is about 25 nm while the inner diameter is about 12 nm. They are found in eukaryotic cells and are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin. Microtubules are very important in a number of cellular processes. They are involved in maintaining structure of the cell and together with microfilamentsand intermediate filaments, they form the cytoskeleton. They also make up the internal structure of cilia and flagella.They provide platforms for intracellular transport and are involved in a variety of cellular processes, including the movement of secretory vesicles, organelles, and intracellular substances (see entries for dynein and kinesin). They are also involved in cell division (mitosis and meiosis) including the formation of mitotic spindles, which are used to pull apart eukaryotic chromosomes.
Flagellum
a long cellular appendage specialized for locomotion. The flagella of prokaryotes and eukaryotes differ in both structure and function. a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The primary role of the flagellum is locomotion but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure. There are large differences between different types of flagellum; the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion, however both are used for swimming. An example of a flagellate bacterium is the ulcer-causing Helicobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic flagellate cell is the mammalian sperm cell, which uses its flagellum to propel itself through the female reproductive tract.[6] Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are sometimes made according to function and/or length.
Contractile vacuole
contractile vacuole, regulatory organelle, usually spherical, found in freshwater protozoa and lower metazoans, such as sponges and hydras, that collects excess fluid from the protoplasm and periodically empties it into the surrounding medium. It may also excrete nitrogenous wastes. In amoebas it changes position with the animal's movement; in most ciliates it follows a definite path through the cell; in the Euglena and other flagellates it remains stationary. The filling and emptying cycle may last from seconds to a minute, depending on the species.
Cytoplasmic streaming
cytoplasmic streaming, also called protoplasmic streaming, the movement of the fluid substance (cytoplasm) within a plant or animal cell. The motion transports nutrients, proteins, and organelles within cells. First discovered in the 1830s, the presence of cytoplasmic streaming helped convince biologists that cells were the fundamental units of life. Although the mechanism of cytoplasmic streaming is not completely understood, it is thought to be mediated by "motor" proteins—molecules made up of two proteins that use adenosine triphosphate (ATP) to move one protein in relation to the other. If one of the proteins remains fixed on a substrate, such as a microfilament or a microtubule, the motor proteins can move organelles and other molecules through the cytoplasm. Motor proteins often consist of actin filaments, long protein fibers aligned in rows parallel to the streaming just inside the cell membrane. Myosin molecules attached to cellular organelles move along the actin fibers, towing the organelles and sweeping other cytoplasmic contents in the same direction.
secondary cell wall
is a structure found in many plant cells, located between the primary cell wall and the plasma membrane. The cell starts producing the secondary cell wall after the primary cell wall is complete and the cell has stopped expanding. Secondary cell walls provide additional protection to cells and rigidity and strength to the larger plant. These walls are constructed of layered sheaths of cellulose microfibrils, wherein the fibers are in parallel within each layer. The inclusion of lignin makes the secondary cell wall less flexible and less permeable to water than the primary cell wall. In addition to making the walls more resilient to degradation, the hydrophobic nature of lignin within these tissues is essential for containing water within the vascular tissues that carry it throughout the plant. The secondary cell wall consists primarily of cellulose, along with other polysaccharides, lignin, and glycoprotein. It sometimes consists of three distinct layers where the direction of the cellulose microfibrils differs between the layers. Wood consists mostly of secondary cell wall, and holds the plant up against gravity
phagocytosis
is the process of engulfing a solid particle by a phagocyte or a protist to form an internal phagosome . Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solids such as bacteria, and is, therefore, distinct from other forms of endocytosis such as the vesicular internalization of various liquids. Phagocytosis is involved in the acquisition of nutrients for some cells, and, in the immune system, it is a major mechanism used to remove pathogens and cell debris. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized. The process is homologous to eating only at the level of single-celled organisms; in multicellular animals, the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes, except in the case of the animal Trichoplax.
stroma
stroma refers to the colourless fluid surrounding the grana within the chloroplast. Within the stroma are grana, stacks of thylakoids, the sub-organelles, where photosynthesis is commenced before the chemical changes completed in the stroma.
thylakoid
the contents of a chloroplast are partitioned from the cytosol by an envelope consisting of at least two membranes separated by a very narrow intermembtane space. inside the chloroplast is another membranous system in the form of flattened, interconnected sacs called thylakoids. in some regions, thylakoids are stacked like poker chips; each stack is called a granum. the fluid outside the thylakoids is the stroma, which contains the chloroplast DNA and ribosomes as well as many enzymes.
mitochondrial matrix
the mitochondrion is enclosed by two membranes, each a phospholipid bilayer with a unique collection of embedded proteins. the outer membrane is smooth but the inner membrane is convoluted with infoldings called cristae. the inner membrane divides the mitochondrion into two internal compartments. the first is the intermembrane space, the narrow region between the inner and outer membranes. the second compartment, the mitochondrial matrix, is enclosed by the inner membrane. the matrix contains many different enzymes as well as the mitochondrial DNA and ribosomes. some of the metabolic steps of cellular respiration are catalyzed by enzymes in the matrix. other proteins that function in respiration, including the enzyme that makes ATP are built into the inner membrane.
Cristae
the mitochondrion is enclosed by two membranes, each a phospholipid bilayer with a unique collection of embedded proteins. the outer membrane is smooth but the inner membrane is convoluted with infoldings called cristae. the inner membrane divides the mitochondrion into two internal compartments. the first is the intermembrane space, the narrow region between the inner and outer membranes. the second compartment, the mitochondrial matrix, is enclosed by the inner membrane. the matrix contains many different enzymes as well as the mitochondrial DNA and ribosomes. some of the metabolic steps of cellular respiration are catalyzed by enzymes in the matrix. other proteins that function in respiration, including the enzyme that makes ATP are built into the inner membrane. as highly folded surfaces, the cristae give the inner mitochondrial membrane a large surface are for these proteins, thus enhancing the productivity of cellular respiration. this is an example of structure fitting function.
nucleus
the nucleus contains most of the genes in the eukaryotic cells. some genes are located in mitochondria and chloroplasts. it is generally the most conspicuous organelle in eukaryotic cells, averaging about 5 micrometers in diameter. the nucleus is enclosed in the nuclear envelope which separates its contents from the cytoplasm.
transmission electron microscope
this is a type of electron microscope. cell biologists use the TEM mainly to study the internal ultra structure of cells. the TEM aims an electron beam through a very thin section of the specimen, similar to the way a light microscope transmits light through a slide. the specimen has been stained with atoms of heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell more than others. the electron passing through the specimen are scattered more in the denser regions, so fewer electrons are transmitted. the image created by the pattern of transmitted electrons. instead of using glass lenses, the TEM uses electromagnets as lenses to bend the paths of the electrons, ultimately focusing the image onto a screen for viewing or onto photographic film.
ultracentrafuge
ultracentrifuges are the most powerful machines and can spin as fast as 130,000 revolutions per minute (rpm) and apply forces o particles of more than one million times the force of gravity. this machine is used in cell fractionation to spin test tubes holding mixtures of disrupted cells at various speeds, separating the cell components by size and density.
transport vesicle
vesicles are miniscule membrane-enclosed sacs within the cell organelles of eukaryotic cells. These sacs help transport or absorb proteins, enzymes and other cell necessities. Inside the membrane sac of a vesicle are macromolecules that require the ability to move beyond cell walls. The membrane encompassing the sac fuses with the outer cell wall to allow these macromolecules to pass through. Vesicles are important parts of human cells, although they also appear in other multicellular organisms. The cell organelles of eukaryotic cells require a transportation system in order to exchange essential materials. Depending on the type of cell, vesicles transport proteins or enzymes, absorb food cells, store and release neurotransmitters or perform a number of other functions for organelles. The cell type and purpose determine the specific function of a vesicle.