Difference between revisions of "Cell"

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A Cell has a Nucleus which controls everything in it and here are some things that it controls and what they do:
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=== Definition ===
'''Cytoplasm'''The cytoplasm is where the chemical reactions take place
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'''Cell membrane''' Controls what goes in and out of a cell
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'''noun'''
(Science: cell biology) An autonomous self replicating unit (in principle) that may constitute an organism (in the case of unicellular organisms) or be a sub unit of multicellular organisms in which individual cells may be more or less specialised differentiated) for particular functions.
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''plural: cells''
- The individual units from which tissues of the body are formed. All living organisms are composed of one or more cells.
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- Any small compartment; ''the cells of a honeycomb''.(biology) the basic structural and functional unit of all organisms; cells may exist as independent units of life (as in monads) or may form colonies or tissues as in higher plants and animals.One cell is the lowest denomination of life thought to be possible. Most organisms consist of more than one cell, which become specialised into particular functions towards the cause of the organism as a whole. cells possess many structures inside them that contain and maintain the building blocks of life called organelles. animal cells and plant cells differ fundamentally.
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[sɛl]
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Membrane-bound structure that occur as functional independent unit of life (such as in unicellular organisms, e.g. bacteria, protozoa, etc.), or as structural or fundamental unit in a biological tissue specialized to perform a particular function in multicellular organisms (e.g. plants and animals)
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== Details ==
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=== Overview ===
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A cell is the structural, functional and biological unit of all [[organism]]s. It is an [[autonomous]] self-replicating [[unit]] that may exist as functional independent unit of [[life]] (as in the case of [[unicellular]] [[organism]]), or as sub-unit in a [[multicellular]] [[organism]] (such as in [[plant]]s and [[animal]]s) that is specialized into carrying out particular functions towards the cause of the [[organism]] as a whole.
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=== Types ===
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Cells may be classified into two major types: ''[[prokaryotic]] cells'' (e.g. [[bacterial]] cells) and ''[[eukaryotic]] cells'' (e.g. [[plant]] or [[animal]] cell). The main difference between the two is a well-defined [[nucleus]] surrounded by a membranous [[nuclear envelope]] present only in [[eukaryotic]] cells. Apart from the nucleus, there are other organelles found in eukaryotic cells. These organelles are [[mitochondria]], [[plastid]]s, [[endoplasmic reticulum]], and [[Golgi apparatus]]. These organelles are not present in prokaryotic ells.  Despite these differences, prokaryotic and eukaryotic cells share a number of common features: the genetic information is stored in [[gene]]s, [[protein]]s serve as their main structural material, [[ribosome]]s are used to synthesize [[protein]]s, adenosine triphosphate is the main source of [[metabolic]] [[energy]] to sustain various cellular processes, and a [[cell membrane]] that controls the flow of substances into and out of the cell.
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Cells may be used as a basis to describe organisms as ''unicellular'' or ''multicellular''. Unicellular organisms are those that have only one cell, i.e. single-celled. Examples are prokaryotes and protists. Multicellular organisms are those possessing more than one cell. Examples are plants and animals. The cells of a multicellular organism may share common features and functions. These cells that act as a unit make up a ''tissue''. The fundamental types of tissues in animals are epithelial tissues (or epithelium), nerve tissue, connective tissue, muscle tissue, and vascular tissue. In plants, the different types of tissues are the embryonic or meristematic tissues (such as apical meristem and cambium), the permanent tissues (e.g. epidermis, cork, trichome), and the reproductive tissues (i.e. sporogenous tissues). The permanent tissues may be further classified into fundamental (e.g. parenchyma, collenchyma, sclerenchyma) and complex (e.g. phloem and xylem tissues). Tissues that work in unison to carry out a specific set of functions form an organ. Conversely, the term ''acellular'' pertains to a tissue that is not made of cells or not divided into cells. An example of acellular tissue is the hyphae of certain fungi.
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=== Characteristics ===
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A cell is a [[membrane]]-bound [[structure]] containing a cytoplasm and cytoplasmic structures. The cell membrane is made up of a two layers of phospholipids with embedded proteins. It separates the contents of the cell from its outside environment, as well as regulates what enters and exits the cell. Another interesting feature of the cell membrane is the presence of surface molecules (e.g. glycoproteins, glycolipids, etc.) that act like a ‘signature’ for a cell. Every cell has a different ‘signature’ or ‘marker’ that is thought to function in cell recognition, or in a sort of cellular identification system. Other cells have additional protective cell layer on top a cell membrane, e.g. cell wall in plants, algae, fungi, and certain prokaryotes.
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The liquid component of the cytoplasm surrounding the organelles and other insoluble cytoplasmic structures in an intact cell where a wide variety of cell processes take place is called [[cytosol]]. The cytosol is comprised of water, ions (e.g. potassium, sodium, chloride, bicarbonate, magnesium, and calcium), and diverse [[biomolecules]], such as [[nucleic acid]]s, [[protein]]s, [[lipid]]s, and [[carbohydrate]]s. The potassium ions are greater in number in the cytosol than the surrounding extracellular fluid. It is in the cytosol that many metabolic reactions take place, e.g. osmoregulation, action potential generation, and cell signaling.
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In eukaryotic cells, cellular ''organelles'' are the ''little organs'' inside the cell. These organelles perform special functions. Eukaryotic cells that carry out photosynthesis (e.g. plant cells) would have numerous plastids, especially chloroplast (a type of plastid containing green pigments).  The presence of chloroplasts is one way to distinguish a plant cell from an animal cell. Other organelles that can be found in both plant cell and animal cell are [[nucleus]], [[mitochondria]], [[endoplasmic reticulum]], and [[Golgi apparatus]]. The nucleus is the large organelle that contains the genetic material (DNA) organized into chromosomes. Mitochondria are regarded as the powerhouse of eukaryotic cells. That is because it is the organelle that supplies energy by generating adenosine triphosphate (ATP) through cellular respiration. The endoplasmic reticulum occurs as interconnected network of flattened sacs or tubule involved in lipid synthesis, carbohydrate metabolism, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products (of rough endoplasmic reticulum) to other cell parts like Golgi apparatus. Golgi apparatus is comprised of membrane-bound stacks. It is involved in glycosylation, packaging of molecules for secretion, transporting of lipids within the cell, and giving rise to lysosomes.
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Other cytoplasmic structures are not considered by other references as ''organelles'' because they are bound by a single membrane only in contrast to the aforementioned organelles that are double-membraned. For example, [[lysosome]]s and [[vacuole]]s are not considered by some references as organelles but cytoplasmic structures based on the account above. Lysosomes are single-membraned structures containing various digestive enzymes, and thus, are involved in intracellular digestion. Vacuoles, in turn, are membrane-bound vesicles involved in intracellular secretion, excretion, storage, and digestion. Similarly, [[ribosome]]s are not an organelle but nonetheless are vital cytoplasmic structures found in eukaryotic cells.
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A prokaryotic cell lacks the typical membrane-bound organelles present in a eukaryotic cell. Nevertheless, it may possess certain ''organellar''-like structures such as ''[[carboxysome]]'' (a protein-shell compartment for carbon fixation in some bacteria), ''[[chlorosome]]'' (a light harvesting complex in green sulfur bacteria), and ''[[magnetosome]]'' (found in magnetotactic bacteria), and thylakoid (in some cyanobacteria). It also has a nucleosome, which is not a double-membraned structure but a region in the prokaryotic cell containing nuclear material.
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The mitochondria and plastids have their own DNA (referred to as extranuclear DNA to distinguish it from the DNA found inside the nucleus). These organelles are semi-autonomous and because of this they are suggested to have originated from endosymbiotic bacteria according to the ''[[endosymbiotic theory]]''.
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=== Cell cycle ===
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''[[Cell cycle]]'' pertains to the sequence of growth and division of a cell. In essence, the cell cycle involves the duplication of DNA via DNA replication and this leads to the division of the parent cell, yielding two daughter cells. These processes are essential for cell growth, replication, and division.
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In eukaryotes, the cell cycle is comprised of a series of biological events namely the ''resting phase'', the ''interphase'', the ''cell division''. During the resting phase, the cell is in an inactive, non-cycling state. Interphase is that phase of the cell cycle where the cell next grows in size, its DNA replicated, and makes a copy of the cell's DNA to prepare for the next cell division. The interphase is comprised of three stages: G1, S phase, and G2. The final stage is cell division.
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=== Common biological reactions  ===
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==== Cell division ====
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Cell division is the process in which a ''parent'' cell divides, giving rise to two or more ''daughter'' cells. It is a vital cellular process because it enables growth, repair, and reproduction. In eukaryotes, cell division may be in the form of mitosis or meiosis. In [[mitosis]], the result is two genetically identical cells. In [[meiosis]], the result is four genetically non-identical cells.
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==== Cell growth and metabolism ====
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Cells after dividing will undergo growth. The growth of the cell is enabled by metabolism. Metabolism may be categorized into two: ''[[catabolism]]'' and ''[[anabolism]]''. Catabolism includes a series of degradative chemical reactions that break down complex molecules into smaller units, usually releasing energy in the process. Anabolism includes a sequence of chemical reactions that constructs or synthesizes molecules from smaller units, usually requiring input of energy (ATP) in the process. Thus, biomolecules, such as nucleic acids, proteins, carbohydrates, and lipids are produced, stored, and degraded inside the cell. For example, the site of DNA and mRNA biosyntheses is the nucleus. Proteins, in turn, are synthesized by the ribosomes. Lipid synthesis occurs in  the endoplasmic reticulum.
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==== Cell motility ====
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Some cells have specialized structures involved in locomotion. Flagella, for instance, are long, slender, threadlike, whiplike extensions that enable movement by propulsion. Some flagella though are not used for movement but for sensation and signal transduction, e.g. rod photoreceptor cells of the eye, olfactory receptor neurons of the nose, kinocilium in cochlea of the ear. Cilia are hair-like projections on the surfaces of some cells. Cilia are generally of two kinds: motile cilia (for [[locomotion]]) and non-motile cilia (for sensory). Example of tissue cells with cilia are the epithelia lining the lungs that sweep away fluids or particles. Examples of organisms that have cilia are protozoans that use them for movement.
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=== Research ===
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Cell biology (or cytology) is the scientific study of cells. Robert Hooke was named as the first to discover cells, in 1665. Matthias Jakob Schleiden and Theodor Schwann were the ones who first formulated the [[Cell theory]], in 1839.
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== Supplementary ==
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=== Etymology ===
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* Latin ''cella'', ''cellula'' ("a small room")
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=== Derived term(s) ===
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* cellular (''adjective'')
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* [[cell biology]]
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* [[stem cell]]
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== Further reading ==
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=== See also ===
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* [[cytology]]
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* [[tissue]]
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* [[organelle]]
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* [[cytoplasm]]
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* [[prokaryote]]
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* [[eukaryote]]
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© Biology Online. Content provided and moderated by '''[https://www.biology-online.org/about/ Biology Online Editors]'''
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Latest revision as of 03:43, 7 July 2019

Definition

noun

plural: cells

[sɛl]

Membrane-bound structure that occur as functional independent unit of life (such as in unicellular organisms, e.g. bacteria, protozoa, etc.), or as structural or fundamental unit in a biological tissue specialized to perform a particular function in multicellular organisms (e.g. plants and animals)

Details

Overview

A cell is the structural, functional and biological unit of all organisms. It is an autonomous self-replicating unit that may exist as functional independent unit of life (as in the case of unicellular organism), or as sub-unit in a multicellular organism (such as in plants and animals) that is specialized into carrying out particular functions towards the cause of the organism as a whole.


Types

Cells may be classified into two major types: prokaryotic cells (e.g. bacterial cells) and eukaryotic cells (e.g. plant or animal cell). The main difference between the two is a well-defined nucleus surrounded by a membranous nuclear envelope present only in eukaryotic cells. Apart from the nucleus, there are other organelles found in eukaryotic cells. These organelles are mitochondria, plastids, endoplasmic reticulum, and Golgi apparatus. These organelles are not present in prokaryotic ells. Despite these differences, prokaryotic and eukaryotic cells share a number of common features: the genetic information is stored in genes, proteins serve as their main structural material, ribosomes are used to synthesize proteins, adenosine triphosphate is the main source of metabolic energy to sustain various cellular processes, and a cell membrane that controls the flow of substances into and out of the cell.


Cells may be used as a basis to describe organisms as unicellular or multicellular. Unicellular organisms are those that have only one cell, i.e. single-celled. Examples are prokaryotes and protists. Multicellular organisms are those possessing more than one cell. Examples are plants and animals. The cells of a multicellular organism may share common features and functions. These cells that act as a unit make up a tissue. The fundamental types of tissues in animals are epithelial tissues (or epithelium), nerve tissue, connective tissue, muscle tissue, and vascular tissue. In plants, the different types of tissues are the embryonic or meristematic tissues (such as apical meristem and cambium), the permanent tissues (e.g. epidermis, cork, trichome), and the reproductive tissues (i.e. sporogenous tissues). The permanent tissues may be further classified into fundamental (e.g. parenchyma, collenchyma, sclerenchyma) and complex (e.g. phloem and xylem tissues). Tissues that work in unison to carry out a specific set of functions form an organ. Conversely, the term acellular pertains to a tissue that is not made of cells or not divided into cells. An example of acellular tissue is the hyphae of certain fungi.


Characteristics

A cell is a membrane-bound structure containing a cytoplasm and cytoplasmic structures. The cell membrane is made up of a two layers of phospholipids with embedded proteins. It separates the contents of the cell from its outside environment, as well as regulates what enters and exits the cell. Another interesting feature of the cell membrane is the presence of surface molecules (e.g. glycoproteins, glycolipids, etc.) that act like a ‘signature’ for a cell. Every cell has a different ‘signature’ or ‘marker’ that is thought to function in cell recognition, or in a sort of cellular identification system. Other cells have additional protective cell layer on top a cell membrane, e.g. cell wall in plants, algae, fungi, and certain prokaryotes.


The liquid component of the cytoplasm surrounding the organelles and other insoluble cytoplasmic structures in an intact cell where a wide variety of cell processes take place is called cytosol. The cytosol is comprised of water, ions (e.g. potassium, sodium, chloride, bicarbonate, magnesium, and calcium), and diverse biomolecules, such as nucleic acids, proteins, lipids, and carbohydrates. The potassium ions are greater in number in the cytosol than the surrounding extracellular fluid. It is in the cytosol that many metabolic reactions take place, e.g. osmoregulation, action potential generation, and cell signaling.


In eukaryotic cells, cellular organelles are the little organs inside the cell. These organelles perform special functions. Eukaryotic cells that carry out photosynthesis (e.g. plant cells) would have numerous plastids, especially chloroplast (a type of plastid containing green pigments). The presence of chloroplasts is one way to distinguish a plant cell from an animal cell. Other organelles that can be found in both plant cell and animal cell are nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus. The nucleus is the large organelle that contains the genetic material (DNA) organized into chromosomes. Mitochondria are regarded as the powerhouse of eukaryotic cells. That is because it is the organelle that supplies energy by generating adenosine triphosphate (ATP) through cellular respiration. The endoplasmic reticulum occurs as interconnected network of flattened sacs or tubule involved in lipid synthesis, carbohydrate metabolism, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products (of rough endoplasmic reticulum) to other cell parts like Golgi apparatus. Golgi apparatus is comprised of membrane-bound stacks. It is involved in glycosylation, packaging of molecules for secretion, transporting of lipids within the cell, and giving rise to lysosomes.


Other cytoplasmic structures are not considered by other references as organelles because they are bound by a single membrane only in contrast to the aforementioned organelles that are double-membraned. For example, lysosomes and vacuoles are not considered by some references as organelles but cytoplasmic structures based on the account above. Lysosomes are single-membraned structures containing various digestive enzymes, and thus, are involved in intracellular digestion. Vacuoles, in turn, are membrane-bound vesicles involved in intracellular secretion, excretion, storage, and digestion. Similarly, ribosomes are not an organelle but nonetheless are vital cytoplasmic structures found in eukaryotic cells.


A prokaryotic cell lacks the typical membrane-bound organelles present in a eukaryotic cell. Nevertheless, it may possess certain organellar-like structures such as carboxysome (a protein-shell compartment for carbon fixation in some bacteria), chlorosome (a light harvesting complex in green sulfur bacteria), and magnetosome (found in magnetotactic bacteria), and thylakoid (in some cyanobacteria). It also has a nucleosome, which is not a double-membraned structure but a region in the prokaryotic cell containing nuclear material.


The mitochondria and plastids have their own DNA (referred to as extranuclear DNA to distinguish it from the DNA found inside the nucleus). These organelles are semi-autonomous and because of this they are suggested to have originated from endosymbiotic bacteria according to the endosymbiotic theory.


Cell cycle

Cell cycle pertains to the sequence of growth and division of a cell. In essence, the cell cycle involves the duplication of DNA via DNA replication and this leads to the division of the parent cell, yielding two daughter cells. These processes are essential for cell growth, replication, and division.

In eukaryotes, the cell cycle is comprised of a series of biological events namely the resting phase, the interphase, the cell division. During the resting phase, the cell is in an inactive, non-cycling state. Interphase is that phase of the cell cycle where the cell next grows in size, its DNA replicated, and makes a copy of the cell's DNA to prepare for the next cell division. The interphase is comprised of three stages: G1, S phase, and G2. The final stage is cell division.


Common biological reactions

Cell division

Cell division is the process in which a parent cell divides, giving rise to two or more daughter cells. It is a vital cellular process because it enables growth, repair, and reproduction. In eukaryotes, cell division may be in the form of mitosis or meiosis. In mitosis, the result is two genetically identical cells. In meiosis, the result is four genetically non-identical cells.


Cell growth and metabolism

Cells after dividing will undergo growth. The growth of the cell is enabled by metabolism. Metabolism may be categorized into two: catabolism and anabolism. Catabolism includes a series of degradative chemical reactions that break down complex molecules into smaller units, usually releasing energy in the process. Anabolism includes a sequence of chemical reactions that constructs or synthesizes molecules from smaller units, usually requiring input of energy (ATP) in the process. Thus, biomolecules, such as nucleic acids, proteins, carbohydrates, and lipids are produced, stored, and degraded inside the cell. For example, the site of DNA and mRNA biosyntheses is the nucleus. Proteins, in turn, are synthesized by the ribosomes. Lipid synthesis occurs in the endoplasmic reticulum.


Cell motility

Some cells have specialized structures involved in locomotion. Flagella, for instance, are long, slender, threadlike, whiplike extensions that enable movement by propulsion. Some flagella though are not used for movement but for sensation and signal transduction, e.g. rod photoreceptor cells of the eye, olfactory receptor neurons of the nose, kinocilium in cochlea of the ear. Cilia are hair-like projections on the surfaces of some cells. Cilia are generally of two kinds: motile cilia (for locomotion) and non-motile cilia (for sensory). Example of tissue cells with cilia are the epithelia lining the lungs that sweep away fluids or particles. Examples of organisms that have cilia are protozoans that use them for movement.


Research

Cell biology (or cytology) is the scientific study of cells. Robert Hooke was named as the first to discover cells, in 1665. Matthias Jakob Schleiden and Theodor Schwann were the ones who first formulated the Cell theory, in 1839.



Supplementary

Etymology

  • Latin cella, cellula ("a small room")

Derived term(s)


Further reading

See also



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