Organelle

organized cell-level biological structure of distinctive morphology and function From Wikipedia, the free encyclopedia

Organelle
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In cell biology, an organelle is a part of a cell that does a specific job.

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A typical animal cell. Within the cytoplasm, the major organelles and cellular structures include: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (6) Golgi apparatus (7) cytoskeleton (8) smooth endoplasmic reticulum (9) mitochondria (10) vacuole (11) cytosol (12) lysosome (13) centriole.

Organelles usually have a plasma membrane around them.[1] Most of the cell's organelles are in the cytoplasm.[2][3]

The name organelle comes from the idea that these Structures are to cells what an organ is to the body.

There are many types of organelles in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been found.[4] They are not organized like eukaryote organelles, and are not bounded by plasma membranes. They are called bacterial microcompartments.[5]

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Scope of the term

The term is now widely used to refer to cell structures surrounded by single or double plasma membranes.[6][7][8][9] However, the older definition of a 'subcellular functional unit' still exists. So, the term is sometimes used for structures which are not membrane-bound.[10][11]

The plasma membrane is a lipid bilayer with some proteins embedded in it. It keeps the ions and molecules of the organelle from merging with the surroundings.

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Origin of organelles

Mitochondria and chloroplasts have double-membranes and their DNA. These are believed to come from incompletely digested or invading prokaryotes, which were adopted as a part of the invaded cell. This idea is supported in the endosymbiotic theory.

Eukaryotic organelles

Major organelles

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Minor organelles

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Prokaryotic organelles

Prokaryotes are not so complex as eukaryotes. They were once thought to have no internal structures inside the lipid membranes.[12]

However, recent research has shown that at least some prokaryotes have microcompartments such as carboxysomes. These subcellular compartments are 100–200 nm in diameter and are enclosed by a shell of proteins.[13] Even more striking is the description of membrane-bound magnetosomes in bacteria.[14][15] as well as the nucleus-like structures of the Planctomycetes that are surrounded by lipid membranes.[16]

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References

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