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66-464: In culture they exhibit much less clumping than many other suspension lines, presumably due to the downregulation of surface adhesion molecules by bcr:abl. However, another study suggests that bcr:abl over-expression may actually increase cell adherence to cell culture plastic. K562 cells can spontaneously develop characteristics similar to early-stage erythrocytes , granulocytes and monocytes and are easily killed by natural killer cells as they lack

132-400: A cell decreases the production and quantities of its cellular components , such as RNA and proteins , in response to an external stimulus. The complementary process that involves increase in quantities of cellular components is called upregulation. An example of downregulation is the cellular decrease in the expression of a specific receptor in response to its increased activation by

198-420: 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

264-869: 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

330-516: 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

396-454: 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

462-434: 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

528-407: 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

594-766: A drug of abuse in adolescence or adulthood causes addiction by inducing stable downregulation or upregulation in expression of specific genes and microRNAs through epigenetic alterations . Such downregulation or upregulation has been shown to occur in the brain's reward regions, such as the nucleus accumbens . DNA damage appears to be the primary underlying cause of cancer. DNA damage can also increase epigenetic alterations due to errors during DNA repair. Such mutations and epigenetic alterations can give rise to cancer (see malignant neoplasms ). Investigation of epigenetic down- or upregulation of repaired DNA genes as possibly central to progression of cancer has been regularly undertaken since 2000. Epigenetic downregulation of

660-414: 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

726-405: 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

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792-427: 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

858-596: A molecule, such as a hormone or neurotransmitter , which reduces the cell's sensitivity to the molecule. This is an example of a locally acting ( negative feedback ) mechanism. An example of upregulation is the response of liver cells exposed to such xenobiotic molecules as dioxin . In this situation, the cells increase their production of cytochrome P450 enzymes , which in turn increases degradation of these dioxin molecules. Downregulation or upregulation of an RNA or protein may also arise by an epigenetic alteration. Such an epigenetic alteration can cause expression of

924-427: 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

990-435: 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

1056-436: 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

1122-461: 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

1188-443: 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

1254-423: A receptor, they effectively direct the cell to do something, such as dividing, dying, or allowing substances to be created, or to enter or exit the cell. A cell's ability to respond to a chemical message depends on the presence of receptors tuned to that message. The more receptors a cell has that are tuned to the message, the more the cell will respond to it. Receptors are created, or expressed, from instructions in

1320-458: 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

1386-460: 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

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1452-507: Is also important in the cell cycle regulation of K562 cells. This gene targets the cyclin-dependent kinase inhibitor, p21, and causes cell differentiation, cell cycle arrest in G1, and ultimately apoptosis. When the levels of these components are thrown off, they can either no longer inhibit apoptosis of the cancer cells, a role fulfilled by BCR/ABL, or they cause apoptosis to be induced, in the same vein as Bax and cytochrome C. These components are key in

1518-403: Is an important regulation mechanism of cancer, because it prevents cells from progressing into mitosis. Apoptosis is an important mechanism in regulating K562 cells and can be induced by the changes in the metabolic state of the cells. There are many different cellular components involved in the cycle of apoptosis such as BCR/ABL, Bcl-2, Bax protein, and cytochrome C. The tumor suppressor gene p53

1584-407: Is an overabundance of Aurora kinases. These kinases play a role in the formation of spindles, separation of chromosomes, as well as cytokinesis. These functions are necessary in cells in order to divide and regenerate tissues, and play a maintenance role in homeostatic functions. However, the overabundance of Aurora kinases allows for uncontrolled cellular division, resulting in cancer. Inhibiting these

1650-697: 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

1716-576: 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

1782-415: Is gradually reduced by the accelerated rate of receptor internalization and degradation brought about by increased hormonal binding. The rate of synthesis of new receptors within the endoplasmic reticulum and their insertion in the plasma membrane do not keep pace with their rate of destruction. Over time, this self-induced loss of target cell receptors for insulin reduces the target cell's sensitivity to

1848-781: 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

1914-510: 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

1980-442: Is the more common process of insulin resistance , which leads to adult-onset diabetes. Another example can be seen in diabetes insipidus , in which the kidneys become insensitive to arginine vasopressin . Family-based, adoption, and twin studies have indicated that there is a strong (50%) heritable component to vulnerability to substance abuse addiction. Especially among genetically vulnerable individuals, repeated exposure to

2046-467: Is typically seen in animal hormone receptors. Upregulation of receptors, on the other hand, can result in super-sensitized cells, especially after repeated exposure to an antagonistic drug or prolonged absence of the ligand. Some receptor agonists may cause downregulation of their respective receptors, while most receptor antagonists temporarily upregulate their respective receptors. The disequilibrium caused by these changes often causes withdrawal when

K562 cells - Misplaced Pages Continue

2112-509: Is upregulated in the majority of cancers of the breast, prostate, stomach, neuroblastomas, pancreas, and lung. 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

2178-566: The MHC complex required to inhibit NK activity. They also lack any trace of Epstein-Barr virus and other herpesviruses. In addition to the Philadelphia chromosome they also exhibit a second reciprocal translocation between the long arm of chromosome 15 with chromosome 17 . Two sub-lines are available which express MHC class-I A2 and A3. K562 cells are part of the NCI-60 cancer cell line panel used by

2244-466: The National Cancer Institute . Many factors and components play a role in the cell cycle of K562 cells in terms of growth, cell differentiation, and apoptosis. The growth of these leukemic cells are controlled by either initiating cell differentiation or apoptosis to occur. Cell differentiation is induced by the deacetylase activity in these “undifferentiated progenitor cells,” which alters

2310-401: 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

2376-611: 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

2442-559: The DNA of the cell, and they can be increased, or upregulated, when the signal is weak, or decreased, or downregulated, when it is strong. Their level can also be up or down regulated by modulation of systems that degrade receptors when they are no longer required by the cell. Downregulation of receptors can also occur when receptors have been chronically exposed to an excessive amount of a ligand, either from endogenous mediators or from exogenous drugs. This results in ligand -induced desensitization or internalization of that receptor. This

2508-417: The DNA repair gene MGMT occurs in 93% of bladder cancers, 88% of stomach cancers, 74% of thyroid cancers, 40–90% of colorectal cancers, and 50% of brain cancers. Similarly, epigenetic downregulation of LIG4 occurs in 82% of colorectal cancers and epigenetic downregulation of NEIL1 occurs in 62% of head and neck cancers and in 42% of non-small-cell lung cancers . Epigenetic upregulation of

2574-537: The DNA repair genes PARP1 and FEN1 occurs in numerous cancers (see Regulation of transcription in cancer ). PARP1 and FEN1 are essential genes in the error-prone and mutagenic DNA repair pathway microhomology-mediated end joining . If this pathway is upregulated, the excess mutations it causes can lead to cancer. PARP1 is over-expressed in tyrosine kinase-activated leukemias, in neuroblastoma, in testicular and other germ cell tumors, and in Ewing's sarcoma. FEN1

2640-452: The RNA or protein to no longer respond to an external stimulus. This occurs, for instance, during drug addiction or progression to cancer . All living cells have the ability to receive and process signals that originate outside their membranes, which they do by means of proteins called receptors , often located at the cell's surface imbedded in the plasma membrane. When such signals interact with

2706-467: 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

K562 cells - Misplaced Pages Continue

2772-488: 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

2838-416: 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

2904-444: 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

2970-509: The cell to program death at this point. The ability to induce these changes in K562 cell cycle and cell cycle regulation provides targets for cancer drugs. One of these drugs is Imatinib, which inhibits BCR/ABL causing growth to cease and apoptosis to begin. Another important group of regulators of the K562 line are Sirtuins, referred to as SIRTS. These play a role in cellular stress, metabolism, and autophagy, by interacting with deacetylases activity in

3036-449: 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

3102-411: The cell. Other methods being focused on in the regulation of K562 cells include therapeutic methods like polyphyllin D, which caused differentiation from the progenitor state to occur, and for apoptosis to begin. Downregulation In biochemistry , in the biological context of organisms ' regulation of gene expression and production of gene products , downregulation is the process by which

3168-436: 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

3234-911: 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

3300-493: 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

3366-478: The elevated hormone concentration. This process is illustrated by the insulin receptor sites on target cells, e.g. liver cells, in a person with type 2 diabetes . Due to the elevated levels of blood glucose in an individual, the β-cells ( islets of Langerhans ) in the pancreas must release more insulin than normal to meet the demand and return the blood to homeostatic levels. The near-constant increase in blood insulin levels results from an effort to match

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3432-633: 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

3498-465: 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

3564-523: 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

3630-405: The increase in blood glucose, which will cause receptor sites on the liver cells to downregulate and decrease the number of receptors for insulin, increasing the subject's resistance by decreasing sensitivity to this hormone. There is also a hepatic decrease in sensitivity to insulin . This can be seen in the continuing gluconeogenesis in the liver even when blood glucose levels are elevated. This

3696-399: 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,

3762-412: The long-term use of a drug is discontinued. Upregulation and downregulation can also happen as a response to toxins or hormones . An example of upregulation in pregnancy is hormones that cause cells in the uterus to become more sensitive to oxytocin . Elevated levels of the hormone insulin in the blood trigger downregulation of the associated receptors. When insulin binds to its receptors on

3828-432: 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

3894-469: The mitochondria, and due to this, it has been supported that apoptosis uses the mitochondrial apoptosis pathway. The offset of these cellular components from their balance point causes morphological changes, which result in the K562 cells being arrested in the G2/M phase of the cell cycle. This arrest leads to “shrinkage, blebbing, nuclear fragmentation, chromatin condensing” and other morphological changes that cause

3960-455: 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

4026-442: The phenotype and morphology of the K562 cells. The change in phenotype induces a decrease in the growth rate and leads the K562 cells to the terminal path of becoming mature erythroids, monocytes, and mature macrophages. These changes can also drive the leukemic cells to a state of stress, which allows for increased sensitivity of the cells to drugs that initiate apoptosis. The problem with K562 cells, and many other cancer cell types,

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4092-409: 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

4158-443: 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

4224-418: The surface of a cell, the hormone receptor complex undergoes endocytosis and is subsequently attacked by intracellular lysosomal enzymes . The internalization of the insulin molecules provides a pathway for degradation of the hormone, as well as for regulation of the number of sites that are available for binding on the cell surface. At high plasma concentrations, the number of surface receptors for insulin

4290-748: 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

4356-434: 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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