Difference between revisions of "Ribosomes"

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What are ribosomes?
=== Definition ===
[[Ribosomes]] are responsible for assembling the [[Proteins]] of the [[Cell]]. Ribosomal [[Subunits]] are synthesized by the [[Nucleolus]]. Depending on the [[Protein]] [[Production]] level of a [[Particular]] [[Cell]], [[Ribosomes]] may [[Number]] in the millions.
[[Ribosome]] attached to [[Endoplasmic reticulum]], [[Image]] courtesy of The Virtual [[Cell]].
What are their distinguishing characteristics?
[[Ribosomes]] are typically composed of [[Two]] subunits: a [[Large]] [[Subunit]] and a [[Small]] [[Subunit]]. These [[Two]] [[Units]] [[Join]] together when the [[Ribosome]] [[Attaches]] to [[Messenger rna]] to [[Produce]] a [[Protein]] in the [[Cytoplasm]] (cyto-).
[[Small]] and [[Large]] [[Ribosome]] [[Subunits]], [[Image]] courtesy of The Virtual [[Cell]].
[[There]] are [[Two]] [[Places]] that [[Ribosomes]] usually [[Exist]] in the cell: suspended in the [[Cytosol]] and [[Bound]] to the [[Endoplasmic reticulum]]. These [[Ribosomes]] are called [[Free]] [[Ribosomes]] and [[Bound]] [[Ribosomes]] respectively. In both [[Cases]], the [[Ribosomes]] usually [[Form]] [[Aggregates]] called polysomes (poly-) ([[Also]] known as polyribosomes).
[[Liver]] [[Cell]] [[Ribosomes]] and polyribosomes, [[Copyright]] Dennis Kunkel.
[[Free]] [[Ribosomes]] usually [[Make]] [[Proteins]] that will [[Function]] in the [[Cytosol]] [[While]] [[Bound]] [[Ribosomes]] usually [[Make]] [[Proteins]] that are exported or [[Included]] in the [[Cells]] [[Membranes]]. Interestingly [[Enough]], [[Free]] [[Ribosomes]] and [[Bound]] [[Ribosomes]] are interchangeable and the [[Cell]] can [[Change]] their [[Numbers]] according to [[Metabolic]] [[Needs]].
''singular: ribosome''
Plural form of '''[[ribosome]]''', i.e. any of the small round particles in a cell made up of RNA and protein that are primarily involved in the assembly of proteins by translating messenger RNA (a process called translation)
[[Ribosomes]] - [[Protein]] CONSTRUCTION TEAMS
[[Cells]] [[Need]] to [[Make]] [[Proteins]]. Those [[Proteins]] [[Might]] be used as [[Enzymes]] or as [[Support]] for other [[Cell]] [[Functions]]. When you [[Need]] to [[Make]] [[Proteins]], you [[Look]] for [[Ribosomes]]. [[Ribosomes]] are the [[Protein]] builders or the [[Protein]] synthesizers of the [[Cell]]. They are [[Like]] construction guys who [[Take]] one [[Amino acid]] at a [[Time]] and [[Build]] [[Long]] [[Protein]] [[Chains]].
[[Ribosomes]] could be in [[Many]] [[Places]] around the [[Cell]]. You [[Might]] [[Find]] them [[Floating]] in the [[Cytoplasm]]. Those [[Floating]] [[Ribosomes]] [[Make]] [[Proteins]] that will be used [[Inside]] of the [[Cell]]. Other [[Ribosomes]] are found on the [[Endoplasmic reticulum]]. [[Endoplasmic reticulum]] with [[Ribosomes]] attached is called [[Rough]]. It [[Looks]] bumpy [[Under]] a [[Microscope]]. Those attached [[Ribosomes]] [[Make]] [[Proteins]] that will be used [[Inside]] the [[Cell]] and [[Proteins]] made for [[Export]] ([[Outside]] the [[Cell]]).
[[Two]] [[Pieces]]
=== See: [[Ribosome]] for further information. ===
A [[Ribosome]] is not [[Just]] one [[Piece]]. [[There]] are [[Two]] [[Pieces]] or [[Subunits]]. Scientists named them 60-S and 30-S. When the [[Cell]] [[Needs]] to [[Make]] [[Protein]], [[Mrna]] is created in the [[Nucleus]]. The [[Mrna]] is then sent [[Into]] the [[Cell]] to the [[Ribosomes]]. When it is [[Time]] to [[Make]] the [[Protein]], the [[Two]] [[Subunits]] come together and combine with the [[Mrna]]. The [[Two]] [[Pieces]] [[Lock]] onto the [[Mrna]] and [[Start]] the [[Protein synthesis]].
[[Mixing]] AND [[Matching]] [[Amino acids]]
The [[Process]] of making [[Proteins]] is quite [[Simple]]. We [[Just]] explained that [[Mrna]] is made in the [[Nucleus]] and sent [[Into]] the [[Cell]]. The [[Mrna]] combines with the [[Ribosome]] [[Subunits]]. Another [[Nucleic acid]] [[Lives]] in the [[Cell]] - [[Trna]], which [[Stands]] for [[Transfer rna]], and it is bonded to [[Amino acids]]. With the [[Mrna]] offering [[Instructions]], the [[Ribosome]] connects to a [[Trna]] and [[Pulls]] [[Off]] the [[Amino acids]]. Slowly the [[Ribosome]] [[Makes]] a [[Long]] [[Amino acid]] [[Chain]] that [[Becomes]] a [[Protein]].
· One or more per [[Cell]] · [[Spherical]] [[Shape]] · Denser than surrounding [[Cytoplasm]]
[[Chromosomes]] - Usually in the [[Form]] of chromatin- Contains [[Genetic]] information- Composed of [[Dna]]- [[Thicken]] for [[Cellular]] division- [[Set]] [[Number]] per [[Species]] (i.e. 23 [[Pairs]] for human)
[[Nuclear membrane]] - Surrounds [[Nucleus]]- Composed of [[Two]] [[Layers]]- Numerous [[Openings]] for [[Nuclear]] [[Traffic]]
[[Nucleolus]] - [[Spherical]] [[Shape]]- [[Visible]] when [[Cell]] is not dividing- Contains [[Rna]] for [[Protein]] manufacture
· Collective [[Term]] for [[Cytosol]] and [[Organelles]] contained [[Within]] · [[Colloidal]] [[Suspension]] · [[Cytosol]] mainly composed of [[Water]] with [[Free]]-[[Floating]] [[Molecules]] · [[Viscosity]] constantly [[Changes]]
Centrioles - [[Paired]] [[Cylindrical]] [[Organelles]] [[Near]] [[Nucleus]]- Composed of [[Nine]] [[Tubes]], each with [[Three]] tubules- [[Involved]] in [[Cellular]] division- [[Lie]] at [[Right]] [[Angles]] to each other
[[Chloroplasts]] - A plastid usually found in [[Plant]] [[Cells]]- Contain [[Green]] [[Chlorophyll]] where [[Photosynthesis]] [[Takes]] [[Place]]
[[Cytoskeleton]] - Composed of microtubules- [[Supports]] [[Cell]] and [[Provides]] [[Shape]]- [[Aids]] [[Movement]] of [[Materials]] in and out of [[Cells]]
[[Endoplasmic reticulum]] - [[Tubular]] [[Network]] fused to [[Nuclear membrane]]- Goes [[Through]] [[Cytoplasm]] onto [[Cell membrane]]- [[Stores]], [[Separates]], and [[Serves]] as [[Cells]] [[Transport]] system- [[Smooth]] type: [[Lacks]] [[Ribosomes]]- [[Rough]] [[Type]] (pictured): [[Ribosomes]] embedded in [[Surface]]
[[Golgi apparatus]] - [[Protein]] 'packaging [[Plant]]- A [[Membrane]] [[Structure]] found [[Near]] [[Nucleus]]- Composed of numerous [[Layers]] forming a [[Sac]]
[[Lysosome]] - [[Digestive]] 'plant' for [[Proteins]], [[Lipids]], and [[Carbohydrates]]- [[Transports]] undigested [[Material]] to [[Cell membrane]] for removal- [[Vary]] in [[Shape]] depending on [[Process]] [[Being]] carried out- [[Cell]] [[Breaks]] [[Down]] if [[Lysosome]] explodes
[[Mitochondria]] - [[Second]] largest [[Organelle]] with unique [[Genetic]] [[Structure]]- Double-layered [[Outer membrane]] with [[Inner]] [[Folds]] called cristae- Energy-producing [[Chemical reactions]] [[Take]] [[Place]] on cristae- [[Controls]] level of [[Water]] and other [[Materials]] in [[Cell]]- Recycles and [[Decomposes]] [[Proteins]], [[Fats]], and [[Carbohydrates]], and [[Forms]] [[Urea]]
[[Ribosomes]] - Each [[Cell]] contains thousands- Miniature 'protein factories'- Composes 25% of [[Cells]] mass- [[Stationary]] type: embedded in [[Rough]] [[Endoplasmic reticulum]]- [[Mobile]] type: injects [[Proteins]] [[Directly]] [[Into]] [[Cytoplasm]]
[[Vacuoles]] - [[Membrane]]-[[Bound]] [[Sacs]] for [[Storage]], [[Digestion]], and [[Waste]] removal- Contains [[Water]] solution- [[Contractile]] [[Vacuoles]] for [[Water]] removal (in [[Unicellular]] organisms)
[[Cell wall]] - Most commonly found in [[Plant]] [[Cells]]- [[Controls]] turgity- [[Extracellular]] [[Structure]] surrounding [[Plasma membrane]]- [[Primary]] [[Cell]] wall: extremely elastic- [[Secondary]] [[Cell]] wall: [[Forms]] around [[Primary cell wall]] after [[Growth]] is complete
[[Plasma membrane]] - [[Outer membrane]] of [[Cell]] that [[Controls]] [[Cellular]] [[Traffic]]- Contains [[Proteins]] ([[Left]], gray) that [[Span]] [[Through]] the [[Membrane]] and allow [[Passage]] of [[Materials]]- [[Proteins]] are surrounded by a [[Phospholipid]] bi-layer.
All living [[Cells]] contain [[Ribosomes]], tiny [[Organelles]] composed of approximately 60 percent [[Ribosomal rna]] ([[Rrna]]) and 40 percent [[Protein]]. [[However]], though they are generally described as [[Organelles]], it is important to [[Note]] that [[Ribosomes]] are not [[Bound]] by a [[Membrane]] and are much smaller than other [[Organelles]]. Some [[Cell]] [[Types]] may [[Hold]] a few million [[Ribosomes]], [[But]] several thousand is more typical. The [[Organelles]] [[Require]] the [[Use]] of an [[Electron microscope]] to be visually detected.
[[Ribosomes]] are mainly found [[Bound]] to the [[Endoplasmic reticulum]] and the [[Nuclear envelope]], as [[Well]] as [[Freely]] [[Scattered]] throughout the [[Cytoplasm]], depending [[Upon]] whether the [[Cell]] is [[Plant]], [[Animal]], or [[Bacteria]]. The [[Organelles]] [[Serve]] as the [[Protein]] [[Production]] machinery for the [[Cell]] and are consequently most [[Abundant]] in [[Cells]] that are [[Active]] in [[Protein synthesis]], such as [[Pancreas]] and [[Brain]] [[Cells]]. Some of the [[Proteins]] synthesized by [[Ribosomes]] are for the [[Cells]] [[Own]] [[Internal]] [[Use]], especially those that are produced by [[Free]] [[Ribosomes]]. [[Many]] of the [[Proteins]] produced by [[Bound]] [[Ribosomes]], [[However]], are transported [[Outside]] of the [[Cell]].
In [[Eukaryotes]], the [[Rrna]] in [[Ribosomes]] is organized [[Into]] four [[Strands]], and in [[Prokaryotes]], [[Three]] [[Strands]]. [[Eukaryote]] [[Ribosomes]] are produced and assembled in the [[Nucleolus]]. Ribosomal [[Proteins]] [[Enter]] the [[Nucleolus]] and combine with the four [[Rrna]] [[Strands]] to create the [[Two]] ribosomal [[Subunits]] (one [[Small]] and one [[Large]]) that will [[Make]] [[Up]] the completed [[Ribosome]] ([[See]] [[Figure]] 1). The [[Ribosome]] [[Units]] [[Leave]] the [[Nucleus]] [[Through]] the [[Nuclear]] [[Pores]] and unite [[Once]] in the [[Cytoplasm]] for the purpose of [[Protein synthesis]]. When [[Protein]] [[Production]] is not [[Being]] carried out, the [[Two]] [[Subunits]] of a [[Ribosome]] are separated.
In 2000, the complete [[Three]]-dimensional [[Structure]] of the [[Large]] and [[Small]] [[Subunits]] of a [[Ribosome]] was established. Evidence based on this [[Structure]] suggests, as had [[Long]] been assumed, that it is the [[Rrna]] that [[Provides]] the [[Ribosome]] with its [[Basic]] [[Formation]] and functionality, not [[Proteins]]. [[Apparently]] the [[Proteins]] in a [[Ribosome]] [[Help]] [[Fill]] in [[Structural]] [[Gaps]] and enhance [[Protein synthesis]], although the [[Process]] can [[Take]] [[Place]] in their [[Absence]], albeit at a much slower [[Rate]].
The [[Units]] of a [[Ribosome]] are often described by their Svedberg (s) [[Values]], which are based [[Upon]] their [[Rate]] of [[Sedimentation]] in a centrifuge. The [[Ribosomes]] in a [[Eukaryotic]] [[Cell]] generally have a Svedberg [[Value]] of 80S and are comprised of 40s and 60s [[Subunits]]. [[Prokaryotic cells]], on the other [[Hand]], contain 70S [[Ribosomes]], each of which consists of a 30s and a 50s [[Subunit]]. As demonstrated by these [[Values]], Svedberg [[Units]] are not [[Additive]], so the [[Values]] of the [[Two]] [[Subunits]] of a [[Ribosome]] do not add [[Up]] to the Svedberg [[Value]] of the [[Entire]] [[Organelle]]. This is because the [[Rate]] of [[Sedimentation]] of a [[Molecule]] depends [[Upon]] its [[Size]] and [[Shape]], rather than simply its [[Molecular weight]].
[[Protein synthesis]] [[Requires]] the [[Assistance]] of [[Two]] other kinds of [[Rna]] [[Molecules]] in [[Addition]] to [[Rrna]]. [[Messenger rna]] ([[Mrna]]) [[Provides]] the [[Template]] of [[Instructions]] from the [[Cellular]] [[Dna]] for building a [[Specific]] [[Protein]]. [[Transfer rna]] ([[Trna]]) [[Brings]] the [[Protein]] building [[Blocks]], [[Amino acids]], to the [[Ribosome]]. [[There]] are [[Three]] [[Adjacent]] [[Trna]] [[Binding sites]] on a ribosome: the aminoacyl [[Binding Site]] for a [[Trna]] [[Molecule]] attached to the [[Next]] [[Amino acid]] in the [[Protein]] (as illustrated in [[Figure]] 1), the peptidyl [[Binding Site]] for the central [[Trna]] [[Molecule]] containing the [[Growing]] [[Peptide]] [[Chain]], and an [[Exit]] [[Binding Site]] to [[Discharge]] used [[Trna]] [[Molecules]] from the [[Ribosome]].
[[Once]] the [[Protein]] [[Backbone]] [[Amino acids]] are polymerized, the [[Ribosome]] [[Releases]] the [[Protein]] and it is transported to the [[Cytoplasm]] in [[Prokaryotes]] or to the [[Golgi apparatus]] in [[Eukaryotes]]. [[There]], the [[Proteins]] are completed and released [[Inside]] or [[Outside]] the [[Cell]]. [[Ribosomes]] are very [[Efficient]] [[Organelles]]. A [[Single]] [[Ribosome]] in a [[Eukaryotic]] [[Cell]] can add 2 [[Amino acids]] to a [[Protein]] [[Chain]] [[Every]] [[Second]]. In [[Prokaryotes]], [[Ribosomes]] can [[Work]] [[Even]] faster, adding about 20 [[Amino acids]] to a [[Polypeptide]] [[Every]] [[Second]].
In [[Addition]] to the most familiar [[Cellular]] locations of [[Ribosomes]], the [[Organelles]] can [[Also]] be found [[Inside]] [[Mitochondria]] and the [[Chloroplasts]] of [[Plants]]. These [[Ribosomes]] notably [[Differ]] in [[Size]] and makeup than other [[Ribosomes]] found in [[Eukaryotic cells]], and are more [[Akin]] to those [[Present]] in [[Bacteria]] and [[Blue-green algae]] [[Cells]]. The similarity of [[Mitochondrial]] and [[Chloroplast]] [[Ribosomes]] to [[Prokaryotic]] [[Ribosomes]] is generally considered [[Strong]] supportive evidence that [[Mitochondria]] and [[Chloroplasts]] evolved from [[Ancestral]] [[Prokaryotes]].

Latest revision as of 00:04, 18 August 2019



singular: ribosome

Plural form of ribosome, i.e. any of the small round particles in a cell made up of RNA and protein that are primarily involved in the assembly of proteins by translating messenger RNA (a process called translation)

See: Ribosome for further information.