Editing Cell (biology) (section)

=== Organelles ===

{{main|Organelle}}

Organelles are parts of the cell that are adapted and/or specialized for carrying out one or more vital functions, analogous to the [[Organ (biology)|organs]] of the human body (such as the heart, lung, and kidney, with each organ performing a different function).<ref name="NCBI"/> 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 a cell. Some (such as the [[Cell nucleus|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.

==== Eukaryotic ====

[[File:HeLa cells stained with Hoechst 33258.jpg|thumb|Human cancer cells, specifically [[HeLa cells]], with DNA stained blue. The central and rightmost cell are in [[interphase]], so their DNA is diffuse and the entire nuclei are labelled. The cell on the left is going through [[mitosis]] and its chromosomes have condensed.]]

* '''Cell nucleus''': A cell's information center, the [[cell nucleus]] is the most conspicuous organelle found in a [[eukaryotic]] cell. It houses the cell's [[chromosomes]], and is the place where almost all [[DNA]] replication and [[RNA]] synthesis ([[Transcription (genetics)|transcription]]) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the [[nuclear envelope]], space between these two membrane is called perinuclear space. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, [[DNA]] is [[Transcription (genetics)|transcribed]], or copied into a special [[RNA]], called [[messenger RNA]] (mRNA). This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The [[nucleolus]] is a specialized region within the nucleus where ribosome subunits are assembled. In prokaryotes, DNA processing takes place in the [[cytoplasm]].<ref name="NCBI"/>
* '''Mitochondria and chloroplasts''': generate energy for the cell. [[Mitochondrion|Mitochondria]] are self-replicating double membrane-bound organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells.<ref name="NCBI"/> [[Cellular respiration|Respiration]] occurs in the cell mitochondria, which generate the cell's energy by [[oxidative phosphorylation]], using [[oxygen]] to release energy stored in cellular nutrients (typically pertaining to [[glucose]]) to generate [[adenosine triphosphate|ATP]] ([[aerobic respiration]]). Mitochondria multiply by [[binary fission]], like prokaryotes. Chloroplasts can only be found in plants and algae, and they capture the sun's energy to make carbohydrates through [[photosynthesis]].

[[File:Endomembrane system diagram en.svg|thumb|upright=1.25|Diagram of the [[endomembrane system]] ]]

* '''Endoplasmic reticulum''': The [[endoplasmic reticulum]] (ER) is a transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes.<ref name="NCBI"/> The smooth ER plays a role in calcium sequestration and release and also helps in synthesis of [[lipid]].
* '''Golgi apparatus''': The primary function of the Golgi apparatus is to process and package the [[macromolecule]]s such as [[protein]]s and [[lipid]]s that are synthesized by the cell.
* '''Lysosomes and peroxisomes''': [[Lysosome]]s contain [[digestive enzyme]]s (acid [[hydrolase]]s). They digest excess or worn-out [[organelle]]s, food particles, and engulfed [[virus]]es or [[bacteria]]. [[Peroxisome]]s have enzymes that rid the cell of toxic [[peroxide]]s, Lysosomes are optimally active in an acidic environment. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system.<ref name="NCBI"/>
* '''Centrosome''': the cytoskeleton organizer: The [[centrosome]] produces the [[microtubules]] of a cell—a key component of the [[cytoskeleton]]. It directs the transport through the [[endoplasmic reticulum|ER]] and the [[Golgi apparatus]]. Centrosomes are composed of two [[centrioles]] which lie perpendicular to each other in which each has an organization like a [[Cart wheel|cartwheel]], which separate during [[cell division]] and help in the formation of the [[mitotic spindle]]. A single centrosome is present in the animal cells. They are also found in some fungi and algae cells.
* '''Vacuoles''': [[Vacuole]]s sequester waste products and in plant cells store water. They are often described as liquid filled spaces and are surrounded by a membrane. Some cells, most notably ''[[Amoeba (genus)|Amoeba]]'', have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of plant cells and fungal cells are usually larger than those of animal cells. Vacuoles of plant cells are surrounded by a membrane which transports ions against concentration gradients.

==== Eukaryotic and prokaryotic ====

* '''Ribosomes''': The [[ribosome]] is a large complex of [[RNA]] and [[protein]] molecules.<ref name="NCBI"/> They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane in prokaryotes).<ref>{{cite journal  |last1=Ménétret |first1=Jean-François |last2=Schaletzky |first2=Julia |last3=Clemons |first3=William M. |last4=Osborne |first4=Andrew R. |last5=Skånland |first5=Sigrid S. |last6=Denison |first6=Carilee |last7=Gygi |first7=Steven P. |last8=Kirkpatrick |first8=Don S. |last9=Park |first9=Eunyong |last10=Ludtke |first10=Steven J. |last11=Rapoport |first11=Tom A. |last12=Akey |first12=Christopher W. |display-authors=3 |title=Ribosome binding of a single copy of the SecY complex: implications for protein translocation |journal=Molecular Cell |volume=28 |issue=6 |pages=1083–1092 |date=December 2007 |pmid=18158904 |doi=10.1016/j.molcel.2007.10.034 |url=https://authors.library.caltech.edu/90566/2/1-s2.0-S1097276507008258-mmc1.pdf |doi-access=free |access-date=2020-09-01 |archive-date=2021-01-21 |archive-url=https://web.archive.org/web/20210121115905/https://authors.library.caltech.edu/90566/2/1-s2.0-S1097276507008258-mmc1.pdf |url-status=live }}</ref>
* '''Plastids''': [[Plastid]] are membrane-bound organelle generally found in plant cells and [[Euglenid|euglenoids]] and contain specific ''pigments'', thus affecting the colour of the plant and organism. And these pigments also helps in food storage and tapping of light energy. There are three types of plastids based upon the specific pigments. [[Chloroplast]]s contain [[chlorophyll]] and some carotenoid pigments which helps in the tapping of light energy during photosynthesis. [[Chromoplast]]s contain fat-soluble [[carotenoid]] pigments like orange carotene and yellow xanthophylls which helps in synthesis and storage. [[Leucoplast]]s are non-pigmented plastids and helps in storage of nutrients.<ref>{{cite book |last=Sato |first=N. |year=2006 |pages=75–102 |title=The Structure and Function of Plastids |volume=23 |editor1=Wise, R. R. |editor2=Hoober, J. K. |publisher=Springer |chapter=Origin and Evolution of Plastids: Genomic View on the Unification and Diversity of Plastids |isbn=978-1-4020-4060-3 |doi=10.1007/978-1-4020-4061-0_4 |series=Advances in Photosynthesis and Respiration}}</ref>