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55-477: Kisra , also spelled kissra ( Sudanese Arabic: [ˈkisra] ), is a popular thin fermented bread made in Chad , Sudan , South Sudan , Algeria and some parts of Uganda and Kenya . It is made from durra or wheat . There are two different forms of kisra : thin baked sheets, known as kisra rhaheeefa , which is similar to injera ; and a porridge known as kisra aseeda or aceda . The latter

110-420: A membrane that envelops the cell, regulates what moves in and out (selectively permeable), and maintains the electric potential of the cell . Inside the membrane, the cytoplasm takes up most of the cell's volume. Except red blood cells , which lack a cell nucleus and most organelles to accommodate maximum space for hemoglobin , all cells possess DNA , the hereditary material of genes , and RNA , containing

165-869: A microscope . Cells emerged on Earth about 4 billion years ago. All cells are capable of replication , protein synthesis , and motility . Cells are broadly categorized into two types: eukaryotic cells , which possess a nucleus , and prokaryotic cells , which lack a nucleus but have a nucleoid region. Prokaryotes are single-celled organisms such as bacteria , whereas eukaryotes can be either single-celled, such as amoebae , or multicellular , such as some algae , plants , animals , and fungi . Eukaryotic cells contain organelles including mitochondria , which provide energy for cell functions; chloroplasts , which create sugars by photosynthesis , in plants; and ribosomes , which synthesise proteins. Cells were discovered by Robert Hooke in 1665, who named them after their resemblance to cells inhabited by Christian monks in

220-516: A nucleus , and other membrane-bound organelles . The DNA of a prokaryotic cell consists of a single circular chromosome that is in direct contact with the cytoplasm . The nuclear region in the cytoplasm is called the nucleoid . Most prokaryotes are the smallest of all organisms, ranging from 0.5 to 2.0 μm in diameter. A prokaryotic cell has three regions: Plants , animals , fungi , slime moulds , protozoa , and algae are all eukaryotic . These cells are about fifteen times wider than

275-454: A cell. Some (such as the nucleus and Golgi apparatus ) are typically solitary, while others (such as mitochondria , chloroplasts , peroxisomes and lysosomes ) can be numerous (hundreds to thousands). The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles. Many cells also have structures which exist wholly or partially outside the cell membrane. These structures are notable because they are not protected from

330-434: A discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory ). A human cell has genetic material contained in the cell nucleus (the nuclear genome ) and in the mitochondria (the mitochondrial genome ). In humans, the nuclear genome is divided into 46 linear DNA molecules called chromosomes , including 22 homologous chromosome pairs and

385-407: A diverse range of single-celled organisms. The plants were created around 1.6 billion years ago with a second episode of symbiogenesis that added chloroplasts , derived from cyanobacteria . In 1665, Robert Hooke examined a thin slice of cork under his microscope , and saw a structure of small enclosures. He wrote "I could exceeding plainly perceive it to be all perforated and porous, much like

440-414: A fluid mosaic membrane. Embedded within this membrane is a macromolecular structure called the porosome the universal secretory portal in cells and a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. The membrane is semi-permeable, and selectively permeable, in that it can either let a substance ( molecule or ion ) pass through freely, to

495-405: A functional three-dimensional protein molecule. Unicellular organisms can move in order to find food or escape predators. Common mechanisms of motion include flagella and cilia . In multicellular organisms, cells can move during processes such as wound healing, the immune response and cancer metastasis . For example, in wound healing in animals, white blood cells move to the wound site to kill

550-427: A limited extent or not at all. Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones . The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis , the uptake of external materials by a cell, and cytokinesis , the separation of daughter cells after cell division ; and moves parts of

605-427: A monastery. Cell theory , developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann , states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from pre-existing cells. Cells are broadly categorized into two types: eukaryotic cells , which possess a nucleus , and prokaryotic cells , which lack

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660-435: A nucleus but have a nucleoid region. Prokaryotes are single-celled organisms , whereas eukaryotes can be either single-celled or multicellular . Prokaryotes include bacteria and archaea , two of the three domains of life . Prokaryotic cells were the first form of life on Earth, characterized by having vital biological processes including cell signaling . They are simpler and smaller than eukaryotic cells, and lack

715-436: A pair of sex chromosomes . The mitochondrial genome is a circular DNA molecule distinct from nuclear DNA. Although the mitochondrial DNA is very small compared to nuclear chromosomes, it codes for 13 proteins involved in mitochondrial energy production and specific tRNAs. Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection . This can be transient, if

770-453: A person's risk for esophageal squamous cell carcinoma ." Cell (biology) The cell is the basic structural and functional unit of all forms of life . Every cell consists of cytoplasm enclosed within a membrane ; many cells contain organelles , each with a specific function. The term comes from the Latin word cellula meaning 'small room'. Most cells are only visible under

825-461: A process called eukaryogenesis . This is widely agreed to have involved symbiogenesis , in which archaea and bacteria came together to create the first eukaryotic common ancestor. This cell had a new level of complexity and capability, with a nucleus and facultatively aerobic mitochondria . It evolved some 2 billion years ago into a population of single-celled organisms that included the last eukaryotic common ancestor, gaining capabilities along

880-443: A process of nuclear division, called mitosis , followed by division of the cell, called cytokinesis . A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells. DNA replication , or the process of duplicating a cell's genome, always happens when a cell divides through mitosis or binary fission. This occurs during

935-458: A typical prokaryote and can be as much as a thousand times greater in volume. The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization : the presence of membrane-bound organelles (compartments) in which specific activities take place. Most important among these is a cell nucleus , an organelle that houses the cell's DNA . This nucleus gives the eukaryote its name, which means "true kernel (nucleus)". Some of

990-460: Is encoded in its DNA sequence. RNA is used for information transport (e.g., mRNA ) and enzymatic functions (e.g., ribosomal RNA). Transfer RNA (tRNA) molecules are used to add amino acids during protein translation . Prokaryotic genetic material is organized in a simple circular bacterial chromosome in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside

1045-496: Is an important factor to consider during the fermentation of foods. Failing to completely remove any microbes from equipment and storing vessels may result in the multiplication of harmful organisms within the ferment, potentially increasing the risks of food borne illnesses such as botulism. However, botulism in vegetable ferments is only possible when not properly canned. The production of off smells and discoloration may be indications that harmful bacteria may have been introduced to

1100-697: Is detected. Diverse repair processes have evolved in organisms ranging from bacteria to humans. The widespread prevalence of these repair processes indicates the importance of maintaining cellular DNA in an undamaged state in order to avoid cell death or errors of replication due to damage that could lead to mutation . E. coli bacteria are a well-studied example of a cellular organism with diverse well-defined DNA repair processes. These include: nucleotide excision repair , DNA mismatch repair , non-homologous end joining of double-strand breaks, recombinational repair and light-dependent repair ( photoreactivation ). Between successive cell divisions, cells grow through

1155-555: Is exacerbated when a plastic container is used for this purpose instead of the old-fashioned, traditional method, a grass-lined hole, as the Clostridium botulinum bacteria thrive in the anaerobic conditions created by the air-tight enclosure in plastic. Research has found that fermented food contains a carcinogenic by-product, ethyl carbamate (urethane). "A 2009 review of the existing studies conducted across Asia concluded that regularly eating pickled vegetables roughly doubles

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1210-597: Is from cyanobacteria -like organisms that lived between 3 and 3.5 billion years ago. Other early fossils of multicellular organisms include the contested Grypania spiralis and the fossils of the black shales of the Palaeoproterozoic Francevillian Group Fossil B Formation in Gabon . The evolution of multicellularity from unicellular ancestors has been replicated in the laboratory, in evolution experiments using predation as

1265-781: Is less well-studied but is involved in the maintenance of cell shape, polarity and cytokinesis. The subunit protein of microfilaments is a small, monomeric protein called actin . The subunit of microtubules is a dimeric molecule called tubulin . Intermediate filaments are heteropolymers whose subunits vary among the cell types in different tissues. Some of the subunit proteins of intermediate filaments include vimentin , desmin , lamin (lamins A, B and C), keratin (multiple acidic and basic keratins), and neurofilament proteins ( NF–L , NF–M ). Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Cells use DNA for their long-term information storage. The biological information contained in an organism

1320-437: Is made use of when fruit juices are converted to wine , when grains are made into beer , and when foods rich in starch, such as potatoes , are fermented and then distilled to make spirits such as gin and vodka . The production of carbon dioxide is used to leaven bread. The production of organic acids is exploited to preserve and flavor vegetables and dairy products. Food fermentation serves five main purposes: to enrich

1375-510: Is present in some bacteria outside the cell membrane and cell wall. The capsule may be polysaccharide as in pneumococci , meningococci or polypeptide as Bacillus anthracis or hyaluronic acid as in streptococci . Capsules are not marked by normal staining protocols and can be detected by India ink or methyl blue , which allows for higher contrast between the cells for observation. Flagella are organelles for cellular mobility. The bacterial flagellum stretches from cytoplasm through

1430-445: Is then used in fermented batter that contains starter from fungal or bacterial fermentation . This bread -related article is a stub . You can help Misplaced Pages by expanding it . Fermentation in food processing The term "fermentation" sometimes refers specifically to the chemical conversion of sugars into ethanol , producing alcoholic drinks such as wine , beer , and cider . However, similar processes take place in

1485-623: Is usually paired with a meat and vegetable stew, such as mullah . As of 1995, the then-undivided country of Sudan ate an estimated 20,000 to 30,000 short tons (18,000 to 27,000 t) of sorghum flour annually in kisra . Traditionally, in Sudanese households, sorghum is used as a base for making Kisra. Sorghum grains are known for having high nutritional value through its minerals and vitamins, which contribute to its anti-inflammatory properties. Two common sorghum varieties are feterita and tabat, which are used to mill fermented flour. This flour

1540-560: The Nobel Prize in Chemistry for his research and discovery of "cell-free fermentation". One year earlier, in 1906, ethanol fermentation studies led to the early discovery of oxidized nicotinamide adenine dinucleotide (NAD ). Food fermentation is the conversion of sugars and other carbohydrates into alcohol or preservative organic acids and carbon dioxide . All three products have found human uses. The production of alcohol

1595-485: The leavening of bread (CO 2 produced by yeast activity), and in the preservation of sour foods with the production of lactic acid , such as in sauerkraut and yogurt . Other widely consumed fermented foods include vinegar , olives , and cheese . More localised foods prepared by fermentation may also be based on beans, grain, vegetables, fruit, honey, dairy products, and fish. Natural fermentation predates human history. Since ancient times, humans have exploited

1650-401: The selective pressure . The origin of cells has to do with the origin of life , which began the history of life on Earth. Small molecules needed for life may have been carried to Earth on meteorites, created at deep-sea vents , or synthesized by lightning in a reducing atmosphere . There is little experimental data defining what the first self-replicating forms were. RNA may have been

1705-614: The DNA is not inserted into the cell's genome , or stable, if it is. Certain viruses also insert their genetic material into the genome. Organelles are parts of the cell that are adapted and/or specialized for carrying out one or more vital functions, analogous to the organs of the human body (such as the heart, lung, and kidney, with each organ performing a different function). Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally simpler and are not membrane-bound. There are several types of organelles in

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1760-467: The S phase of the cell cycle . In meiosis, the DNA is replicated only once, while the cell divides twice. DNA replication only occurs before meiosis I . DNA replication does not occur when the cells divide the second time, in meiosis II . Replication, like all cellular activities, requires specialized proteins for carrying out the job. Cells of all organisms contain enzyme systems that scan their DNA for damage and carry out repair processes when it

1815-488: The attachment of bacteria to specific receptors on human cells ( cell adhesion ). There are special types of pili involved in bacterial conjugation . Cell division involves a single cell (called a mother cell ) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue ) and to procreation ( vegetative reproduction ) in unicellular organisms . Prokaryotic cells divide by binary fission , while eukaryotic cells usually undergo

1870-416: The cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of microtubules , intermediate filaments and microfilaments . In the cytoskeleton of a neuron the intermediate filaments are known as neurofilaments . There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The prokaryotic cytoskeleton

1925-444: The cell membrane(s) and extrudes through the cell wall. They are long and thick thread-like appendages, protein in nature. A different type of flagellum is found in archaea and a different type is found in eukaryotes. A fimbria (plural fimbriae also known as a pilus , plural pili) is a short, thin, hair-like filament found on the surface of bacteria. Fimbriae are formed of a protein called pilin ( antigenic ) and are responsible for

1980-449: The cell, glucose is broken down to make adenosine triphosphate ( ATP ), a molecule that possesses readily available energy, through two different pathways. In plant cells, chloroplasts create sugars by photosynthesis , using the energy of light to join molecules of water and carbon dioxide . Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves

2035-436: The cell. mRNA molecules bind to protein-RNA complexes called ribosomes located in the cytosol , where they are translated into polypeptide sequences. The ribosome mediates the formation of a polypeptide sequence based on the mRNA sequence. The mRNA sequence directly relates to the polypeptide sequence by binding to transfer RNA (tRNA) adapter molecules in binding pockets within the ribosome. The new polypeptide then folds into

2090-911: The cytoskeleton. In August 2020, scientists described one way cells—in particular cells of a slime mold and mouse pancreatic cancer-derived cells—are able to navigate efficiently through a body and identify the best routes through complex mazes: generating gradients after breaking down diffused chemoattractants which enable them to sense upcoming maze junctions before reaching them, including around corners. Multicellular organisms are organisms that consist of more than one cell, in contrast to single-celled organisms . In complex multicellular organisms, cells specialize into different cell types that are adapted to particular functions. In mammals, major cell types include skin cells , muscle cells , neurons , blood cells , fibroblasts , stem cells , and others. Cell types differ both in appearance and function, yet are genetically identical. Cells are able to be of

2145-1650: The diet through development of a diversity of flavors, aromas, and textures in food substrates; to preserve substantial amounts of food through lactic acid , alcohol, acetic acid , and alkaline fermentations; to enrich food substrates with protein, essential amino acids , and vitamins; to eliminate antinutrients ; and to reduce cooking time and the associated use of fuel. Cheonggukjang , doenjang , fermented bean curd , miso , natto , soy sauce , stinky tofu , tempeh , oncom, soybean paste, Beijing mung bean milk, kinama, iru , thua nao Amazake , beer , bread , choujiu , gamju , injera , kvass , makgeolli , murri , ogi , rejuvelac , sake , sikhye , sourdough , sowans , rice wine , malt whisky , grain whisky , idli , dosa , Bangla (drink) vodka , boza , and chicha , among others. Kimchi , mixed pickle , sauerkraut , Indian pickle , gundruk , tursu Wine , vinegar , cider , perry , brandy , atchara , nata de coco , burong mangga , asinan , pickling , vişinată , chocolate , rakı , aragh sagi , chacha , tempoyak Mead , metheglin , tej Some kinds of cheese also, kefir , kumis (mare milk), shubat (camel milk), ayran , cultured milk products such as quark , filmjölk , crème fraîche , smetana , skyr , and yogurt Bagoong , faseekh , fish sauce , Garum , Hákarl , jeotgal , ngapi , padaek , pla ra , prahok , rakfisk , shrimp paste , surströmming , shidal Chorizo , salami , sucuk , pepperoni , nem chua, som moo , saucisson , fermented sausage Pu-erh tea , Kombucha , Lahpet , Goishicha Sterilization

2200-493: The earliest self-replicating molecule , as it can both store genetic information and catalyze chemical reactions. Cells emerged around 4 billion years ago. The first cells were most likely heterotrophs . The early cell membranes were probably simpler and more permeable than modern ones, with only a single fatty acid chain per lipid. Lipids spontaneously form bilayered vesicles in water, and could have preceded RNA. Eukaryotic cells were created some 2.2 billion years ago in

2255-633: The external environment by the cell membrane. In order to assemble these structures, their components must be carried across the cell membrane by export processes. Many types of prokaryotic and eukaryotic cells have a cell wall . The cell wall acts to protect the cell mechanically and chemically from its environment, and is an additional layer of protection to the cell membrane. Different types of cell have cell walls made up of different materials; plant cell walls are primarily made up of cellulose , fungi cell walls are made up of chitin and bacteria cell walls are made up of peptidoglycan . A gelatinous capsule

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2310-423: The fermentation of sugar to alcohol by yeast , Pasteur concluded that the fermentation was catalyzed by a vital force, called " ferments ", within the yeast cells. The "ferments" were thought to function only within living organisms. Pasteur wrote that "Alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells." Nevertheless, it

2365-677: The fermentation process. The earliest archaeological evidence of fermentation is 13,000-year-old residues of a beer, with the consistency of gruel, found in a cave near Haifa in Israel. Another early alcoholic drink, made from fruit, rice, and honey, dates from 7000 to 6600 BC, in the Neolithic Chinese village of Jiahu , and winemaking dates from ca. 6000 BC, in Georgia , in the Caucasus area. Seven-thousand-year-old jars containing

2420-509: The food. Alaska has witnessed a steady increase of cases of botulism since 1985. It has more cases of botulism than any other state in the United States of America. This is caused by the traditional Alaska Native practice of allowing animal products such as whole fish, fish heads, walrus , sea lion , and whale flippers, beaver tails, seal oil, and birds, to ferment for an extended period of time before being consumed. The risk

2475-470: The formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: transcription and translation . Transcription is the process where genetic information in DNA is used to produce a complementary RNA strand. This RNA strand is then processed to give messenger RNA (mRNA), which is free to migrate through

2530-523: The functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism , in which the cell breaks down complex molecules to produce energy and reducing power , and anabolism , in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions. Complex sugars can be broken down into simpler sugar molecules called monosaccharides such as glucose . Once inside

2585-399: The information necessary to build various proteins such as enzymes , the cell's primary machinery. There are also other kinds of biomolecules in cells. This article lists these primary cellular components , then briefly describes their function. The cell membrane , or plasma membrane, is a selectively permeable biological membrane that surrounds the cytoplasm of a cell. In animals,

2640-432: The microorganisms that cause infection. Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins. The process is divided into three steps: protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell body and rear, and cytoskeletal contraction to pull the cell forward. Each step is driven by physical forces generated by unique segments of

2695-455: The other differences are: Many groups of eukaryotes are single-celled. Among the many-celled groups are animals and plants. The number of cells in these groups vary with species; it has been estimated that the human body contains around 37 trillion (3.72×10 ) cells, and more recent studies put this number at around 30 trillion (~36 trillion cells in the male, ~28 trillion in the female). All cells, whether prokaryotic or eukaryotic , have

2750-409: The plasma membrane is the outer boundary of the cell, while in plants and prokaryotes it is usually covered by a cell wall . This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids , which are amphiphilic (partly hydrophobic and partly hydrophilic ). Hence, the layer is called a phospholipid bilayer , or sometimes

2805-660: The remains of wine, now on display at the University of Pennsylvania, were excavated in the Zagros Mountains in Iran . There is strong evidence that people were fermenting alcoholic drinks in Babylon ca. 3000 BC, ancient Egypt ca. 3150 BC, pre-Hispanic Mexico ca. 2000 BC, and Sudan ca. 1500 BC. The French chemist Louis Pasteur founded zymology , when in 1856 he connected yeast to fermentation. When studying

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2860-443: The same genotype but of different cell type due to the differential expression of the genes they contain. Most distinct cell types arise from a single totipotent cell, called a zygote , that differentiates into hundreds of different cell types during the course of development . Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by

2915-748: The uneven distribution of molecules during division ). Multicellularity has evolved independently at least 25 times, including in some prokaryotes, like cyanobacteria , myxobacteria , actinomycetes , or Methanosarcina . However, complex multicellular organisms evolved only in six eukaryotic groups: animals, fungi, brown algae, red algae, green algae, and plants. It evolved repeatedly for plants ( Chloroplastida ), once or twice for animals , once for brown algae , and perhaps several times for fungi , slime molds , and red algae . Multicellularity may have evolved from colonies of interdependent organisms, from cellularization , or from organisms in symbiotic relationships . The first evidence of multicellularity

2970-434: The way, though the sequence of the steps involved has been disputed, and may not have started with symbiogenesis. It featured at least one centriole and cilium , sex ( meiosis and syngamy ), peroxisomes , and a dormant cyst with a cell wall of chitin and/or cellulose . In turn, the last eukaryotic common ancestor gave rise to the eukaryotes' crown group , containing the ancestors of animals , fungi , plants , and

3025-457: Was known that yeast extracts can ferment sugar even in the absence of living yeast cells . While studying this process in 1897, the German chemist and zymologist Eduard Buchner of Humboldt University of Berlin , Germany, found that sugar was fermented even when there were no living yeast cells in the mixture, by an enzyme complex secreted by yeast that he termed zymase . In 1907 he received

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