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114-410: Many species of bacteria are subject to lysis by the enzyme lysozyme , found in animal saliva , egg white , and other secretions . Phage lytic enzymes ( lysins ) produced during bacteriophage infection are responsible for the ability of these viruses to lyse bacterial cells. Penicillin and related β-lactam antibiotics cause the death of bacteria through enzyme-mediated lysis that occurs after

228-420: 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

342-406: A nucleus and rarely harbour membrane -bound organelles . Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor . These evolutionary domains are called Bacteria and Archaea . The word bacteria

456-641: 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

570-516: 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

684-543: A potential difference analogous to a battery. The general lack of internal membranes in bacteria means these reactions, such as electron transport , occur across the cell membrane between the cytoplasm and the outside of the cell or periplasm . However, in many photosynthetic bacteria, the plasma membrane is highly folded and fills most of the cell with layers of light-gathering membrane. These light-gathering complexes may even form lipid-enclosed structures called chlorosomes in green sulfur bacteria . Bacteria do not have

798-404: A terminal electron acceptor in a redox reaction . Chemotrophs are further divided by the types of compounds they use to transfer electrons. Bacteria that derive electrons from inorganic compounds such as hydrogen, carbon monoxide , or ammonia are called lithotrophs , while those that use organic compounds are called organotrophs . Still, more specifically, aerobic organisms use oxygen as

912-744: A bacterial strain. However, liquid growth media are used when the measurement of growth or large volumes of cells are required. Growth in stirred liquid media occurs as an even cell suspension, making the cultures easy to divide and transfer, although isolating single bacteria from liquid media is difficult. The use of selective media (media with specific nutrients added or deficient, or with antibiotics added) can help identify specific organisms. Most laboratory techniques for growing bacteria use high levels of nutrients to produce large amounts of cells cheaply and quickly. However, in natural environments, nutrients are limited, meaning that bacteria cannot continue to reproduce indefinitely. This nutrient limitation has led

1026-400: A cell membrane. This method uses enzymes such as lysozyme or proteases to disintegrate the cell membrane. Bacteria See § Phyla Bacteria ( / b æ k ˈ t ɪər i ə / ; sg. : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell . They constitute a large domain of prokaryotic microorganisms . Typically

1140-454: 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

1254-434: 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

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1368-424: A disorganised slime layer of extracellular polymeric substances to a highly structured capsule . These structures can protect cells from engulfment by eukaryotic cells such as macrophages (part of the human immune system ). They can also act as antigens and be involved in cell recognition, as well as aiding attachment to surfaces and the formation of biofilms. The assembly of these extracellular structures

1482-407: 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

1596-434: A few micrometres in length, bacteria were among the first life forms to appear on Earth , and are present in most of its habitats . Bacteria inhabit the air, soil, water, acidic hot springs , radioactive waste , and the deep biosphere of Earth's crust . Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere . The nutrient cycle includes

1710-413: A few micrometres in thickness to up to half a metre in depth, and may contain multiple species of bacteria, protists and archaea. Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures, such as microcolonies , through which there are networks of channels to enable better diffusion of nutrients. In natural environments, such as soil or

1824-415: A few species are visible to the unaided eye—for example, Thiomargarita namibiensis is up to half a millimetre long, Epulopiscium fishelsoni reaches 0.7 mm, and Thiomargarita magnifica can reach even 2 cm in length, which is 50 times larger than other known bacteria. Among the smallest bacteria are members of the genus Mycoplasma , which measure only 0.3 micrometres, as small as

1938-426: A fixed size and then reproduce through binary fission , a form of asexual reproduction . Under optimal conditions, bacteria can grow and divide extremely rapidly, and some bacterial populations can double as quickly as every 17 minutes. In cell division, two identical clone daughter cells are produced. Some bacteria, while still reproducing asexually, form more complex reproductive structures that help disperse

2052-414: 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

2166-405: 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

2280-427: 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

2394-408: A membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid . The nucleoid contains the chromosome with its associated proteins and RNA . Like all other organisms , bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome

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2508-427: 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

2622-435: 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

2736-436: 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

2850-528: A particular organism or group of organisms ( syntrophy ). Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase , a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The second phase of growth

2964-461: 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

3078-415: A process called transformation . Many bacteria can naturally take up DNA from the environment, while others must be chemically altered in order to induce them to take up DNA. The development of competence in nature is usually associated with stressful environmental conditions and seems to be an adaptation for facilitating repair of DNA damage in recipient cells. Second, bacteriophages can integrate into

3192-443: 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

3306-425: A single continuous stretch of DNA. Although several different types of introns do exist in bacteria, these are much rarer than in eukaryotes. Bacteria, as asexual organisms, inherit an identical copy of the parent's genome and are clonal . However, all bacteria can evolve by selection on changes to their genetic material DNA caused by genetic recombination or mutations . Mutations arise from errors made during

3420-427: A single linear chromosome, while some Vibrio species contain more than one chromosome. Some bacteria contain plasmids , small extra-chromosomal molecules of DNA that may contain genes for various useful functions such as antibiotic resistance , metabolic capabilities, or various virulence factors . Bacteria genomes usually encode a few hundred to a few thousand genes. The genes in bacterial genomes are usually

3534-649: A source of electrons and a substrate for carbon anabolism . In many ways, bacterial metabolism provides traits that are useful for ecological stability and for human society. For example, diazotrophs have the ability to fix nitrogen gas using the enzyme nitrogenase . This trait, which can be found in bacteria of most metabolic types listed above, leads to the ecologically important processes of denitrification , sulfate reduction , and acetogenesis , respectively. Bacterial metabolic processes are important drivers in biological responses to pollution ; for example, sulfate-reducing bacteria are largely responsible for

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3648-797: A thick peptidoglycan cell wall like a Gram-positive bacterium, but also a second outer layer of lipids. In many bacteria, an S-layer of rigidly arrayed protein molecules covers the outside of the cell. This layer provides chemical and physical protection for the cell surface and can act as a macromolecular diffusion barrier . S-layers have diverse functions and are known to act as virulence factors in Campylobacter species and contain surface enzymes in Bacillus stearothermophilus . Flagella are rigid protein structures, about 20 nanometres in diameter and up to 20 micrometres in length, that are used for motility . Flagella are driven by

3762-417: A three- dimensional random walk . Bacterial species differ in the number and arrangement of flagella on their surface; some have a single flagellum ( monotrichous ), a flagellum at each end ( amphitrichous ), clusters of flagella at the poles of the cell ( lophotrichous ), while others have flagella distributed over the entire surface of the cell ( peritrichous ). The flagella of a group of bacteria,

3876-458: 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

3990-460: 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

4104-480: Is caused by a toxin released by the bacteria that grow from the spores. Clostridioides difficile infection , a common problem in healthcare settings, is caused by spore-forming bacteria. Bacteria exhibit an extremely wide variety of metabolic types. The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy , but these traits often do not correspond with modern genetic classifications. Bacterial metabolism

4218-412: Is classified into nutritional groups on the basis of three major criteria: the source of energy , the electron donors used, and the source of carbon used for growth. Phototrophic bacteria derive energy from light using photosynthesis , while chemotrophic bacteria breaking down chemical compounds through oxidation , driving metabolism by transferring electrons from a given electron donor to

4332-536: Is dependent on bacterial secretion systems . These transfer proteins from the cytoplasm into the periplasm or into the environment around the cell. Many types of secretion systems are known and these structures are often essential for the virulence of pathogens, so are intensively studied. Some genera of Gram-positive bacteria, such as Bacillus , Clostridium , Sporohalobacter , Anaerobacter , and Heliobacterium , can form highly resistant, dormant structures called endospores . Endospores develop within

4446-697: 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

4560-534: Is determined by the bacterial cell wall and cytoskeleton and is important because it can influence the ability of bacteria to acquire nutrients, attach to surfaces, swim through liquids and escape predators . Multicellularity . Most bacterial species exist as single cells; others associate in characteristic patterns: Neisseria forms diploids (pairs), streptococci form chains, and staphylococci group together in "bunch of grapes" clusters. Bacteria can also group to form larger multicellular structures, such as

4674-441: Is different from that of eukaryotes and archaea. Some bacteria produce intracellular nutrient storage granules, such as glycogen , polyphosphate , sulfur or polyhydroxyalkanoates . Bacteria such as the photosynthetic cyanobacteria , produce internal gas vacuoles , which they use to regulate their buoyancy, allowing them to move up or down into water layers with different light intensities and nutrient levels. Around

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4788-414: Is essential to the survival of many bacteria, and the antibiotic penicillin (produced by a fungus called Penicillium ) is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan. There are broadly speaking two different types of cell wall in bacteria, that classify bacteria into Gram-positive bacteria and Gram-negative bacteria . The names originate from the reaction of cells to

4902-597: 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

5016-781: 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

5130-529: Is made of about 20 proteins, with approximately another 30 proteins required for its regulation and assembly. The flagellum is a rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane for power. Bacteria can use flagella in different ways to generate different kinds of movement. Many bacteria (such as E. coli ) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and makes their movement

5244-468: Is made primarily of phospholipids . This membrane encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential components of the cytoplasm within the cell. Unlike eukaryotic cells , bacteria usually lack large membrane-bound structures in their cytoplasm such as a nucleus , mitochondria , chloroplasts and the other organelles present in eukaryotic cells. However, some bacteria have protein-bound organelles in

5358-496: Is motile in liquid or solid media. Several Listeria and Shigella species move inside host cells by usurping the cytoskeleton , which is normally used to move organelles inside the cell. By promoting actin polymerisation at one pole of their cells, they can form a kind of tail that pushes them through the host cell's cytoplasm. A few bacteria have chemical systems that generate light. This bioluminescence often occurs in bacteria that live in association with fish, and

5472-510: 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

5586-447: Is the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair , antioxidant metabolism and nutrient transport . The final phase is the death phase where

5700-440: Is the logarithmic phase , also known as the exponential phase. The log phase is marked by rapid exponential growth . The rate at which cells grow during this phase is known as the growth rate ( k ), and the time it takes the cells to double is known as the generation time ( g ). During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth

5814-427: Is the destruction of neoplastic cells or of a tumour . The term is also used to refer to the reduction of any swelling . Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis . In a hypertonic environment, the cell membrane peels off the cell wall and the vacuole collapses. These cells will eventually wilt and die unless the flow of water caused by osmosis can stop

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5928-653: Is the most popular and simple approach. Chemical lysis chemically deteriorates/solubilizes the proteins and lipids present within the membrane of targeted cells. Common lysis buffers contain sodium hydroxide (NaOH) and sodium dodecyl sulfate (SDS). Cell lysis is best done at a pH range of 11.5-12.5. Although simple, it is a slow process, taking anywhere from 6 to 12 hours. This method uses ultrasonic waves to generate areas of high and low pressure which causes cavitation and in turn, cell lysis. Though this method usually comes out clean, it fails to be cost effective and consistent. This method uses physical penetration to pierce or cut

6042-694: Is the plural of the Neo-Latin bacterium , which is the Latinisation of the Ancient Greek βακτήριον ( baktḗrion ), the diminutive of βακτηρία ( baktēría ), meaning "staff, cane", because the first ones to be discovered were rod-shaped . The ancestors of bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were

6156-472: The Gram stain , a long-standing test for the classification of bacterial species. Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids . In contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins . Most bacteria have

6270-546: The decomposition of dead bodies ; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps , extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane , to energy. Bacteria also live in mutualistic , commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in

6384-401: 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

6498-444: The spirochaetes , are found between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Two other types of bacterial motion are called twitching motility that relies on a structure called the type IV pilus , and gliding motility , that uses other mechanisms. In twitching motility, the rod-like pilus extends out from the cell, binds some substrate, and then retracts, pulling

6612-551: The vacuum and radiation of outer space , leading to the possibility that bacteria could be distributed throughout the Universe by space dust , meteoroids , asteroids , comets , planetoids , or directed panspermia . Endospore-forming bacteria can cause disease; for example, anthrax can be contracted by the inhalation of Bacillus anthracis endospores, and contamination of deep puncture wounds with Clostridium tetani endospores causes tetanus , which, like botulism ,

6726-614: 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

6840-793: The Gram-negative cell wall, and only members of the Bacillota group and actinomycetota (previously known as the low G+C and high G+C Gram-positive bacteria, respectively) have the alternative Gram-positive arrangement. These differences in structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only Gram-positive bacteria and is ineffective against Gram-negative pathogens , such as Haemophilus influenzae or Pseudomonas aeruginosa . Some bacteria have cell wall structures that are neither classically Gram-positive or Gram-negative. This includes clinically important bacteria such as mycobacteria which have

6954-467: 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

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7068-425: The archaeal/eukaryotic lineage. The most recent common ancestor (MRCA) of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. The earliest life on land may have been bacteria some 3.22 billion years ago. Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from

7182-455: The atmosphere and one cubic metre of air holds around one hundred million bacterial cells. The oceans and seas harbour around 3 x 10 bacteria which provide up to 50% of the oxygen humans breathe. Only around 2% of bacterial species have been fully studied. Size . Bacteria display a wide diversity of shapes and sizes. Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0.5–5.0  micrometres in length. However,

7296-488: 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

7410-520: The bacteria have come into contact with in the past, which allows them to block virus replication through a form of RNA interference . Third, bacteria can transfer genetic material through direct cell contact via conjugation . In ordinary circumstances, transduction, conjugation, and transformation involve transfer of DNA between individual bacteria of the same species, but occasionally transfer may occur between individuals of different bacterial species, and this may have significant consequences, such as

7524-444: The bacteria perform separate tasks; for example, about one in ten cells migrate to the top of a fruiting body and differentiate into a specialised dormant state called a myxospore, which is more resistant to drying and other adverse environmental conditions. Biofilms . Bacteria often attach to surfaces and form dense aggregations called biofilms and larger formations known as microbial mats . These biofilms and mats can range from

7638-401: The bacteria run out of nutrients and die. Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacteria Carsonella ruddii , to 12,200,000 base pairs (12.2 Mbp) in the soil-dwelling bacteria Sorangium cellulosum . There are many exceptions to this; for example, some Streptomyces and Borrelia species contain

7752-412: The bacterial chromosome, introducing foreign DNA in a process known as transduction . Many types of bacteriophage exist; some infect and lyse their host bacteria, while others insert into the bacterial chromosome. Bacteria resist phage infection through restriction modification systems that degrade foreign DNA and a system that uses CRISPR sequences to retain fragments of the genomes of phage that

7866-502: The breakdown of oil spills , the production of cheese and yogurt through fermentation , the recovery of gold, palladium , copper and other metals in the mining sector ( biomining , bioleaching ), as well as in biotechnology , and the manufacture of antibiotics and other chemicals. Once regarded as plants constituting the class Schizomycetes ("fission fungi"), bacteria are now classified as prokaryotes . Unlike cells of animals and other eukaryotes , bacterial cells do not contain

7980-437: The cell forward. Motile bacteria are attracted or repelled by certain stimuli in behaviours called taxes : these include chemotaxis , phototaxis , energy taxis , and magnetotaxis . In one peculiar group, the myxobacteria, individual bacteria move together to form waves of cells that then differentiate to form fruiting bodies containing spores. The myxobacteria move only when on solid surfaces, unlike E. coli , which

8094-416: 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

8208-444: 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

8322-449: 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

8436-407: The cell. Cytolysis can be prevented by several different mechanisms, including the contractile vacuole that exists in some paramecia , which rapidly pump water out of the cell. Cytolysis does not occur under normal conditions in plant cells because plant cells have a strong cell wall that contains the osmotic pressure, or turgor pressure , that would otherwise cause cytolysis to occur. Oncolysis

8550-436: 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

8664-446: The choice of lysis mechanism; often it is desirable to avoid mechanical shear forces that would denature or degrade sensitive macromolecules, such as proteins and DNA , and different types of detergents can yield different results. The unprocessed solution immediately after lysis but before any further extraction steps is often referred to as a crude lysate . For example, lysis is used in western and Southern blotting to analyze

8778-432: The composition of specific proteins , lipids , and nucleic acids individually or as complexes . Depending on the detergent used, either all or some membranes are lysed. For example, if only the cell membrane is lysed then gradient centrifugation can be used to collect certain organelles . Lysis is also used for protein purification , DNA extraction , and RNA extraction . This method uses chemical disruption. It

8892-563: The contraction of the cell membrane . Erythrocytes' hemoglobin release free radicals in response to pathogens when lysed by them. This can damage the pathogens. Cell lysis is used in laboratories to break open cells and purify or further study their contents. Lysis in the laboratory may be affected by enzymes or detergents or other chaotropic agents . Mechanical disruption of cell membranes, as by repeated freezing and thawing, sonication , pressure, or filtration may also be referred to as lysis. Many laboratory experiments are sensitive to

9006-629: The cytoplasm of the cell; generally, a single endospore develops in each cell. Each endospore contains a core of DNA and ribosomes surrounded by a cortex layer and protected by a multilayer rigid coat composed of peptidoglycan and a variety of proteins. Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, such as high levels of UV light , gamma radiation , detergents , disinfectants , heat, freezing, pressure, and desiccation . In this dormant state, these organisms may remain viable for millions of years. Endospores even allow bacteria to survive exposure to

9120-419: The cytoplasm which compartmentalise aspects of bacterial metabolism, such as the carboxysome . Additionally, bacteria have a multi-component cytoskeleton to control the localisation of proteins and nucleic acids within the cell, and to manage the process of cell division . Many important biochemical reactions, such as energy generation, occur due to concentration gradients across membranes, creating

9234-911: 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

9348-411: The dominant forms of life. Although bacterial fossils exist, such as stromatolites , their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogeny , and these studies indicate that bacteria diverged first from

9462-407: The drug causes the bacterium to form a defective cell wall . If the cell wall is completely lost and the penicillin was used on gram-positive bacteria , then the bacterium is referred to as a protoplast , but if penicillin was used on gram-negative bacteria , then it is called a spheroplast . Cytolysis occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into

9576-493: 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

9690-526: The elongated filaments of Actinomycetota species, the aggregates of Myxobacteria species, and the complex hyphae of Streptomyces species. These multicellular structures are often only seen in certain conditions. For example, when starved of amino acids, myxobacteria detect surrounding cells in a process known as quorum sensing , migrate towards each other, and aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100,000 bacterial cells. In these fruiting bodies,

9804-501: The energy released by the transfer of ions down an electrochemical gradient across the cell membrane. Fimbriae (sometimes called " attachment pili ") are fine filaments of protein, usually 2–10 nanometres in diameter and up to several micrometres in length. They are distributed over the surface of the cell, and resemble fine hairs when seen under the electron microscope . Fimbriae are believed to be involved in attachment to solid surfaces or to other cells, and are essential for

9918-602: The entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes , which are still found in all known Eukarya (sometimes in highly reduced form , e.g. in ancient "amitochondrial" protozoa). Later, some eukaryotes that already contained mitochondria also engulfed cyanobacteria -like organisms, leading to

10032-641: The evolution of different growth strategies (see r/K selection theory ). Some organisms can grow extremely rapidly when nutrients become available, such as the formation of algal and cyanobacterial blooms that often occur in lakes during the summer. Other organisms have adaptations to harsh environments, such as the production of multiple antibiotics by Streptomyces that inhibit the growth of competing microorganisms. In nature, many organisms live in communities (e.g., biofilms ) that may allow for increased supply of nutrients and protection from environmental stresses. These relationships can be essential for growth of

10146-633: 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

10260-570: The formation of chloroplasts in algae and plants. This is known as primary endosymbiosis . Bacteria are ubiquitous, living in every possible habitat on the planet including soil, underwater, deep in Earth's crust and even such extreme environments as acidic hot springs and radioactive waste. There are thought to be approximately 2×10 bacteria on Earth, forming a biomass that is only exceeded by plants. They are abundant in lakes and oceans, in arctic ice, and geothermal springs where they provide

10374-470: 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

10488-523: 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

10602-653: The growth in cell population. 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 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

10716-453: The gut. However, several species of bacteria are pathogenic and cause infectious diseases , including cholera , syphilis , anthrax , leprosy , tuberculosis , tetanus and bubonic plague . The most common fatal bacterial diseases are respiratory infections . Antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. Bacteria are important in sewage treatment and

10830-399: 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,

10944-409: The laboratory. The study of bacteria is known as bacteriology , a branch of microbiology . Like all animals, humans carry vast numbers (approximately 10 to 10 ) of bacteria. Most are in the gut , though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system , and many are beneficial , particularly the ones in

11058-627: The largest viruses . Some bacteria may be even smaller, but these ultramicrobacteria are not well-studied. Shape . Most bacterial species are either spherical, called cocci ( singular coccus , from Greek kókkos , grain, seed), or rod-shaped, called bacilli ( sing . bacillus, from Latin baculus , stick). Some bacteria, called vibrio , are shaped like slightly curved rods or comma-shaped; others can be spiral-shaped, called spirilla , or tightly coiled, called spirochaetes . A small number of other unusual shapes have been described, such as star-shaped bacteria. This wide variety of shapes

11172-716: The light probably serves to attract fish or other large animals. Bacteria often function as multicellular aggregates known as biofilms , exchanging a variety of molecular signals for intercell communication and engaging in coordinated multicellular behaviour. The communal benefits of multicellular cooperation include a cellular division of labour , accessing resources that cannot effectively be used by single cells, collectively defending against antagonists, and optimising population survival by differentiating into distinct cell types. For example, bacteria in biofilms can have more than five hundred times increased resistance to antibacterial agents than individual "planktonic" bacteria of

11286-432: 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

11400-417: The newly formed daughter cells. Examples include fruiting body formation by myxobacteria and aerial hyphae formation by Streptomyces species, or budding. Budding involves a cell forming a protrusion that breaks away and produces a daughter cell. In the laboratory, bacteria are usually grown using solid or liquid media. Solid growth media , such as agar plates , are used to isolate pure cultures of

11514-473: The nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane , to energy. They live on and in plants and animals. Most do not cause diseases, are beneficial to their environments, and are essential for life. The soil is a rich source of bacteria and a few grams contain around a thousand million of them. They are all essential to soil ecology, breaking down toxic waste and recycling nutrients. They are even found in

11628-455: 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

11742-475: The outside of the cell membrane is the cell wall . Bacterial cell walls are made of peptidoglycan (also called murein), which is made from polysaccharide chains cross-linked by peptides containing D- amino acids . Bacterial cell walls are different from the cell walls of plants and fungi , which are made of cellulose and chitin , respectively. The cell wall of bacteria is also distinct from that of achaea, which do not contain peptidoglycan. The cell wall

11856-409: 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

11970-612: The production of the highly toxic forms of mercury ( methyl- and dimethylmercury ) in the environment. Nonrespiratory anaerobes use fermentation to generate energy and reducing power, secreting metabolic by-products (such as ethanol in brewing) as waste. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. Unlike in multicellular organisms, increases in cell size ( cell growth ) and reproduction by cell division are tightly linked in unicellular organisms. Bacteria grow to

12084-560: The replication of DNA or from exposure to mutagens . Mutation rates vary widely among different species of bacteria and even among different clones of a single species of bacteria. Genetic changes in bacterial genomes emerge from either random mutation during replication or "stress-directed mutation", where genes involved in a particular growth-limiting process have an increased mutation rate. Some bacteria transfer genetic material between cells. This can occur in three main ways. First, bacteria can take up exogenous DNA from their environment in

12198-443: 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

12312-530: The same species. One type of intercellular communication by a molecular signal is called quorum sensing , which serves the purpose of determining whether the local population density is sufficient to support investment in processes that are only successful if large numbers of similar organisms behave similarly, such as excreting digestive enzymes or emitting light. Quorum sensing enables bacteria to coordinate gene expression and to produce, release, and detect autoinducers or pheromones that accumulate with

12426-412: The surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices , and bacteria protected within biofilms are much harder to kill than individual isolated bacteria. The bacterial cell is surrounded by a cell membrane , which

12540-457: The terminal electron acceptor, while anaerobic organisms use other compounds such as nitrate , sulfate , or carbon dioxide. Many bacteria, called heterotrophs , derive their carbon from other organic carbon . Others, such as cyanobacteria and some purple bacteria , are autotrophic , meaning they obtain cellular carbon by fixing carbon dioxide . In unusual circumstances, the gas methane can be used by methanotrophic bacteria as both

12654-447: The transfer of antibiotic resistance. In such cases, gene acquisition from other bacteria or the environment is called horizontal gene transfer and may be common under natural conditions. Many bacteria are motile (able to move themselves) and do so using a variety of mechanisms. The best studied of these are flagella , long filaments that are turned by a motor at the base to generate propeller-like movement. The bacterial flagellum

12768-748: 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

12882-495: The virulence of some bacterial pathogens. Pili ( sing . pilus) are cellular appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or sex pili (see bacterial genetics, below). They can also generate movement where they are called type IV pili . Glycocalyx is produced by many bacteria to surround their cells, and varies in structural complexity: ranging from

12996-434: 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

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