Difference between revisions of "Ribosomes"

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What are ribosomes?
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[[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. They are tiny [[Round]] [[Particles]].
[[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-).  
 
[[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).  
 
[[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]].  
 
[[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]].  
  
 
 
 
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[[Ribosomes]] - [[Protein]] CONSTRUCTION TEAMS  
 
[[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]].  
 
[[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]].  
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[[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]]).  
 
[[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]]
 
 
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]].  
 
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]].
 
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]].
 

Revision as of 08:37, 9 July 2006

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. They are tiny Round Particles.

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-).

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).

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.

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).

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.

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.