a mitochondrion

A mitochondrion (Terminologia histologica: Mitochondrion) is a cell organelle of eucaryotes with ovoid shape that is the major source for intracellular energy. Mitochondria are present in all but mature red blood cells. They can migrate through the cytoplasm and change their shape. These organelles have an outer unit membrane (membrana mitochondrialis externa) and an inner membrane (membrana mitochondrialis interna). The latter has protrusions into the matrix (mitochondrial plasma).
Depending on the appearance of the inner membrane mitochondria are classified as:
- mitochondrion of the crista-type (most common, with crest-like protrusions),
- mitochondrion of the tubular-type (in cells synthesising steroids, with larger tubular protrusions),
- mitochondrion of the prismatic-type (present only in rat astrocytes, here the tubuli show triangular profiles)
- mitochondrion of the saccular-type (present only in cells of the fasciculate zone of the suprarenal gland, saccular pearl-like protrusions of the tubuli)
- further there are intermediate forms of crista and tubulus type.
Depending on its protein content the matrix of mitochondria may be dark or bright. In cells of the bone and occasionally in other cells electron dense granules, 25 - 50 nm in diameter, consisting of phospholipids and rich in calcium are present. Mitochondria have their own DNA and RNA necessary for synthesis of specific mitochondrial proteins and autoreproduction. Usually mitochondria are present at intracellular locations where energy is required. They contain specific enzymes, e.g. of the citrate-cycle and for oxidation of fatty acids. Energy is used for synthesis of Adenosine-triphosphate (ATP).
Mitochondrial half-life is thought to be about 5-12 days.

Just as a car's combustion engine converts gasoline into motion, tiny engines nestled inside your cells are converting food and oxygen into a form of energy that your body can use. These cellular powerhouses are known as mitochondria (the singular is "mitochondrion"). They are found in most plant and animal cells, but not in bacteria.
Mitochondria are very efficient energy producers in the presence of oxygen. Although cells have other means of producing energy if oxygen is unavailable, no other process is as efficient as the mitochondrion's method.
Mitochondria are made up of over 1,000 proteins, but only about a dozen of these are encoded in the single, circular piece of DNA that resides in the mitochondria (known as mitochondrial DNA or mtDNA for short). The rest of the proteins that make up the mitochondria are actually encoded in the nuclear genome - the genetic material that sits inside the cell's nucleus.
Mitochondrial DNA is passed from parent to child in a rather unique way. In humans, 23 chromosomes reside in the cellular nucleus. During reproduction both parents pass along genetic information encoded in these chromosomes to an offspring. But the single circle of mitochondrial DNA tends to come from the mother only. This means that the mitochondrial genome undergoes less genetic shuffling, allowing researchers to trace an individual's ancestry through the maternal line using mitochondrial DNA.
It might surprise you to know that mitochondrial DNA has much in common with bacterial DNA, in terms of its overall size and structure. This may be because mitochondria are the descendents of an ancient, free-living bacterium. Scientists hypothesize that billions of years ago, a cell engulfed one of these tiny organisms. Instead of being digested and destroyed, the way most foreign bodies are, it survived and received food and nourishment from its host cell. And in return, the host received energy. This mutually beneficial relationship gave rise to modern mitochondria.
Because of the critical role that mitochondria play in breaking down nutrients and efficiently converting these raw materials into energy packets, any flaws in the mitochondria can have a serious impact on human health. A range of diseases - including neurological disorders, diabetes, Parkinson's, and many others - may be tied to defects in the mitochondrion. Lysome
Lysosomes are cellular organelles that contain acid hydrolase enzymes that break down waste materials and cellular debris. These are non-specific. They can be described as the stomach of the cell. They are found in animal cells, while their existence in yeasts and plants are disputed. Some biologists say the same roles are performed by lytic vacuoles,[1] while others suggest there is strong evidence that lysosomes are indeed in some plant cells.[2] Lysosomes digest excess or worn-out organelles, food particles, and engulf viruses or bacteria. The membrane around a lysosome allows the digestive enzymes to work at the 4.5 pH they require. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus. The name lysosome derives from the Greek words lysis, to separate, and soma, body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in the 1960s.
The size of a lysosome varies from 0.1–1.2 μm.[3] At pH 4.8, the interior of the lysosomes is acidic compared to the slightly alkaline cytosol (pH 7.2). The lysosome maintains this pH differential by pumping protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. The lysosomal membrane protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The cell is additionally protected from any lysosomal acid hydrolases that drain into the cytosol, as these enzymes are pH-sensitive and do not function well or at all in the alkaline environment of the cytosol.This ensures that cytosolic molecules and organelles are not lysed in case there is leakage of the hydrolytic enzymes from the lysosome.
Lysosomes are the cell's waste disposal system and can digest some compounds. They are used for the digestion of macromolecules from phagocytosis (ingestion of other dying cells or larger extracellular material, like foreign invading microbes), endocytosis (where receptor proteins are recycled from the cell surface), and autophagy (where in old or unneeded organelles or proteins, or microbes that have invaded the cytoplasm are delivered to the lysosome). Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis, of the cell, which means that the cell is digesting itself.
Other functions include digesting foreign bacteria (or other forms of waste) that invade a cell and helping repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. In the past, lysosomes were thought to kill cells that are no longer wanted, such as those in the tails of tadpoles or in the web from the fingers of a 3- to 6-month-old fetus.

Nuclear envelop,nucleus, nucleous
The nucleus of a eukaryotic cell contains the DNA, the genetic material of the cell. The DNA contains the information necessary for constructing the cell and directing the multitude of synthesis tasks performed by the cell in the process of life and reproduction.
The nuclear envelope surrounds the nucleus with a double membrane with multiple pores. The pores regulate the passage of macromolecules like proteins and RNA, but permit free passage of water, ions, ATP and other small molecules. In this way the membrane exerts some control over the information flow in the cell since information is carried by the macromolecules.
Inside the nuclear envelope is the chromatin, meaning "colored substance" after the early experiments in which that material was highly colored by the staining techniques used. Chromatin consists of DNA associated with proteins which forms long strands called chromosomes. While the DNA remains in the nucleus, it controls most of the processes that occur in the cytoplasm of the cell. Information from the DNA can be transcribed to mRNA and transmitted to other cellular synthesis processes, and information from the cytoplasm can provide feedback to the nucleus.
The nucleolus is the central portion of the cell nucleus and is composed of ribosomal RNA, proteins and DNA. It also contains ribosomes in

Plant cell
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For the scientific journal, see The Plant Cell.

Plant cell structure
Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic organisms. Their distinctive features include:
A large central vacuole, a water-filled volume enclosed by a membrane known as the tonoplast[1][2] maintains the cell's turgor, controls movement of molecules between the cytosol and sap, stores useful material and digests waste proteins and organelles.
A cell wall composed of cellulose and hemicellulose, pectin and in many cases lignin, is secreted by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi (which are made of chitin), and of bacteria, which are made of peptidoglycan.
Specialized cell to cell communication pathways known as plasmodesmata,[3] pores in the primary cell wall through which the plasmalemma and endoplasmic reticulum[4] of adjacent cells are continuous.
Plastids, the most notable being the chloroplasts, which contain chlorophyll a green coloured pigment which is used for absorbing sunlight and is used by a plant to make its own food in the process is known as photosynthesis. Other types of plastid are the amyloplasts, specialized for starch storage, elaioplasts specialized for fat storage, and chromoplasts specialized for synthesis and storage of pigments. As in mitochondria, which have a genome encoding 37 genes,[5] plastids have their own genomes of about 100–120 unique genes[6] and, it is presumed, arose as prokaryotic endosymbionts living in the cells of an early eukaryotic ancestor of the land plants and algae.[7]
Cell division by construction of a phragmoplast as a template for building a cell plate late in cytokinesis is characteristic of land plants and a few groups of algae, notably the Charophytes[8] and the Order Trentepohliales[9]
The sperm of bryophytes and pteridophytes have flagellae similar to those in animals,[10][11] but higher plants, (including Gymnosperms and flowering plants) lack the flagellae and centrioles[12] that are present in animal cells.
Contents
[hide]
1 Cell types
2 Tissue types
3 Organelles
4 References
[edit] Cell types
Parenchyma cells are living cells that have diverse functions ranging from storage and support to photosynthesis and phloem loading (transfer cells). Apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Some parenchyma cells, as in the epidermis, are specialized for light penetration and focusing or regulation of gas exchange, but others are among the least specialized cells in plant tissue, and may remain totipotent, capable of dividing to produce new populations of undifferentiated cells, throughout their lives. Parenchyma cells have thin, permeable primary walls enabling the transport of small molecules between them, and their cytoplasm is responsible for a wide range of biochemical functions such as nectar secretion, or the manufacture of secondary products that discourage herbivory. Parenchyma cells that contain many chloroplasts and are concerned primarily with photosynthesis are called chlorenchyma cells. Others, such as the majority of the parenchyma cells in potato tubers and the seed cotyledons of legumes, have a storage function.
Collenchyma cells – collenchyma cells are alive at maturity and have only a primary wall. These cells mature from meristem derivatives that initially resemble parenchyma, but differences quickly become apparent. Plastids do not develop, and the secretory apparatus (ER and Golgi) proliferates to secrete additional primary wall. The wall is most commonly thickest at the corners, where three or more cells come in contact, and thinnest where only two cells come in contact, though other arrangements of the wall thickening are possible.[13]
Pectin and hemicellulose are the dominant constituents of collenchyma cell walls of dicotyledon angiosperms, which may contain as little as 20% of cellulose in Petasites.[14] Collenchyma cells are typically quite elongated, and may divide transversely to give a septate appearance. The role of this cell type is to support the plant in axes still growing in length, and to confer flexibility and tensile strength on tissues. The primary wall lacks lignin that would make it tough and rigid, so this cell type provides what could be called plastic support – support that can hold a young stem or petiole into the air, but in cells that can be stretched as the cells around them elongate. Stretchable support (without elastic snap-back) is a good way to describe what collenchyma does. Parts of the strings in celery are collenchyma.
Sclerenchyma cells – Sclerenchyma cells (from the Greek skleros, hard) are hard and tough cells with a function in mechanical support. They are of two broad types – sclereids or stone cells and fibres. The cells develop an extensive secondary cell wall that is laid down on the inside of the primary cell wall. The secondary wall is impregnated with lignin, making it hard and impermeable to water. Thus, these cells cannot survive for long' as they cannot exchange sufficient material to maintain active metabolism. Sclerenchyma cells are typically dead at functional maturity, and the cytoplasm is missing, leaving an empty central cavity.
Functions for sclereid cells (hard cells that give leaves or fruits a gritty texture) include discouraging herbivory, by damaging digestive passages in small insect larval stages, and physical protection (a solid tissue of hard sclereid cells form the pit wall in a peach and many other fruits). Functions of fibres include provision of load-bearing support and tensile strength to the leaves and stems of herbaceous plants.[13] Sclerenchyma fibres are not involved in conduction, either of water and nutrients (as in the xylem) or of carbon compounds (as in the phloem), but it is likely that they may have evolved as modifications of xylem and phloem initials in early land plants.

Animal cell cell membrane - the thin layer of protein and fat that surrounds the cell. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others. centrosome - (also called the "microtubule organizing center") a small body located near the nucleus - it has a dense center and radiating tubules. The centrosomes is where microtubules are made. During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. The centriole is the dense center of the centrosome. cytoplasm - the jellylike material outside the cell nucleus in which the organelles are located.
Golgi body - (also called the Golgi apparatus or golgi complex) a flattened, layered, sac-like organelle that looks like a stack of pancakes and is located near the nucleus. It produces the membranes that surround the lysosomes. The Golgi body packages proteins and carbohydrates into membrane-bound vesicles for "export" from the cell. lysosome - (also called cell vesicles) round organelles surrounded by a membrane and containing digestive enzymes. This is where the digestion of cell nutrients takes place. mitochondrion - spherical to rod-shaped organelles with a double membrane. The inner membrane is infolded many times, forming a series of projections (called cristae). The mitochondrion converts the energy stored in glucose into ATP (adenosine triphosphate) for the cell. nuclear membrane - the membrane that surrounds the nucleus. nucleolus - an organelle within the nucleus - it is where ribosomal RNA is produced. Some cells have more than one nucleolus. nucleus - spherical body containing many organelles, including the nucleolus. The nucleus controls many of the functions of the cell (by controlling protein synthesis) and contains DNA (in chromosomes). The nucleus is surrounded by the nuclear membrane. ribosome - small organelles composed of RNA-rich cytoplasmic granules that are sites of protein synthesis. rough endoplasmic reticulum - (rough ER) a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transports materials through the cell and produces proteins in sacks called cisternae (which are sent to the Golgi body, or inserted into the cell membrane). smooth endoplasmic reticulum - (smooth ER) a vast system of interconnected, membranous, infolded and convoluted tubes that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). The space within the ER is called the ER lumen. Smooth ER transports materials through the cell. It contains enzymes and produces and digests lipids (fats) and membrane proteins; smooth ER buds off from rough ER, moving the newly-made proteins and lipids to the Golgi body, lysosomes, and membranes. vacuole - fluid-filled, membrane-surrounded cavities inside a cell. The vacuole fills with food being digested and waste material that is on its way out of the cell.

Goligi body

The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells.[1] It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898.[2]
Part of the cellular endomembrane system, the Golgi apparatus packages proteins inside the cell before they are sent to their destination; it is particularly important in the processing of proteins for secretion.
Contents
Found within the cytoplasm of both plant and animal cells, the Golgi is composed of stacks of membrane-bound structures known as cisternae (singular: cisterna). An individual stack is sometimes called a dictyosome (from Greek dictyon: net + soma: body),[4] especially in plant cells.[5] A mammalian cell typically contains 40 to 100 stacks.[6] Between four and eight cisternae are usually present in a stack; however, in some protists as many as sixty have been observed.[3] Each cisterna comprises a flat, membrane enclosed disc that includes special Golgi enzymes which modify or help to modify cargo proteins that travel through it.[7]
The cisternae stack has four functional regions: the cis-Golgi network, medial-Golgi, endo-Golgi, and trans-Golgi network. Vesicles from the endoplasmic reticulum (via the vesicular-tubular clusters) fuse with the network and subsequently progress through the stack to the trans Golgi network, where they are packaged and sent to their destination. Each region contains different enzymes which selectively modify the contents depending on where they reside.[8] The cisternae also carry structural proteins important for their maintenance as flattened membranes which stack upon each other.[9]

Cells synthesise a large number of different macromolecules. The Golgi apparatus is integral in modifying, sorting, and packaging these macromolecules for cell secretion[10] (exocytosis) or use within the cell.[11] It primarily modifies proteins delivered from the rough endoplasmic reticulum but is also involved in the transport of lipids around the cell, and the creation of lysosomes.[11] In this respect it can be thought of as similar to a post office; it packages and labels items which it then sends to different parts of the cell.

Endoplasmic ER

here are two types of endoplasmic reticulum: rough endoplasmic reticulum(rough ER) and smooth endoplasmic reticulum (smooth ER). Both types are present in plant and animal cells. The two types of ER are separate entities and are not joined together. Cells specialising in the production of proteins will tend to have a larger amount of rough ER whilst cells producing lipids (fats) and steroid hormones will have a greater amount of smooth ER.
Part of the rough ER is continuous with the nuclear envelope. The Golgi apparatus is also closely associated with the ER and recent observations suggest that parts of the two organelles, i.e. the ER and the Golgi complex, are so close that some chemical products probably pass directly between them instead of being packaged into vesicles (droplets enclosed within a membrane) and transported to them through the cytoplasm
ROUGH ENDOPLASMIC RETICULUM
This is an extensive organelle composed of a greatly convoluted but flattish sealed sac that is continuous with the nuclear membrane. It is called 'rough' endoplasmic reticulum because it is studded on its outer surface (the surface in contact with the cytosol) with ribosomes. These are called membrane bound ribosomes and are firmly attached to the outer cytosolic side of the ER About 13 million ribosomes are present on the RER in the average liver cell. Rough ER is found throughout the cell but the density is higher near the nucleus and the Golgi apparatus.
Ribosomes on the rough endoplasmic reticulum are called 'membrane bound' and are responsible for the assembly of many proteins. This process is called translation. Certain cells of the pancreas and digestive tract produce a high volume of protein as enzymes. Many of the proteins are produced in quantity in the cells of the pancreas and the digestive tract and function as digestive enzymes.
The rough ER working with membrane bound ribosomes takes polypeptides and amino acids from the cytosol and continues protein assembly including, at an early stage, recognising a 'destination label' attached to each of them. Proteins are produced for the plasma membrane, Golgi apparatus, secretory vesicles, plant vacuoles, lysosomes, endosomes and the endoplasmic reticulum itself. Some of the proteins are delivered into the lumen or space inside the ER whilst others are processed within the ER membrane itself. In the lumen some proteins have sugar groups added to them to form glycoproteins. Some have metal groups added to them. It is in the rough ER for example that four polypeptide chains are brought together to form haemoglobin.
Protein folding unit
It is in the lumen of the rough ER that proteins are folded to produce the highly important biochemical architecture which will provide 'lock and key' and other recognition and linking sites.
Protein quality control section
It is also in the lumen that an amazing process of quality control checking is carried out. Proteins are subjected to a quality control check and any that are found to be incorrectly formed or incorrectly folded are rejected. These rejects are stored in the lumen or sent for recycling for eventual breakdown to amino acids. A type of emphysema (a lung problem) is caused by the ER quality control section continually rejecting an incorrectly folded protein. The protein is wrongly folded as a result of receiving an altered genetic message. The required protein is never exported from the lumen of rough ER. Research into protein structure failures relating to HIV are also focusing on reactions in the ER
Rigorous quality control plays a part in cystic fibrosis
A form of cystic fibrosis is caused by a missing single amino acid, phenylanaline, in a particular position in the protein construction. The protein might work well without the amino acid but the very exacting service provided by the quality control section spots the error and rejects the protein retaining it in the lumen of the rough ER. In this case the customer (the person with cystic fibrosis) loses out completely due to high standards when a slightly poorer product would have been better than no product at all.
From Rough ER to Golgi
In most cases proteins are transferred to the Golgi apparatus for 'finishing'. They are conveyed in vesicles or possibly directly between the ER and Golgi surfaces. After 'finishing' they are delivered to specific locations.
SMOOTH ENDOPLASMIC RETICULUM
Smooth ER is more tubular than rough ER and forms a separate sealed interconnecting network. It is found fairly evenly distributed throughout the cytoplasm.
It is not studded with ribosomes hence 'smooth ER'.
Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products. In liver cells for example smooth ER enables glycogen that is stored as granules on the external surface of smooth ER to be broken down to glucose. Smooth ER is also involved in the production of steroid hormones in the adrenal cortex and endocrine glands.
Smooth ER - the detox stop
Smooth ER also plays a large part in detoxifying a number of organic chemicals converting them to safer water-soluble products.
Large amounts of smooth ER are found in liver cells where one of its main functions is to detoxify products of natural metabolism and to endeavour to detoxify overloads of ethanol derived from excess alcoholic drinking and also barbiturates from drug overdose. To assist with this, smooth ER can double its surface area within a few days, returning to its normal size when the assault has subsided.
The contraction of muscle cells is triggered by the orderly release of calcium ions. These ions are released from the smooth endoplasmic reticulum.