Dictionary » R » Ribosomes



noun, singular: ribosome

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, being entirely particulate, are not considered organelles when the term organelle is strictly used to refer to membraned structures. Although in some literature they are referred to as "non-membranous organelles". Ribosomes are typically composed of two subunits: the large and small subunits. They join as one during translation; together, they catalyze the translation of mRNA into a polypeptide chain during protein synthesis, and since their active sites are made of RNA, ribosomes are also referred to as "ribozymes."

Ribosomes are formed in the cytoplasm of prokaryotic cells. In eukaryotic cells, they are formed most often in the nucleolus. Another difference between ribosomes of prokaryotes and eukaryotes is the structure of the ribosomes. Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit. Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit. However, the organelles like chloroplasts and mitochondria that are present only in eukaryotic cells also consist of 70S ribosomes resembling those in prokaryotes (e.g. bacteria), indicating that these eukaryotic organelles have descended from their ancestral bacteria (see Endosymbiotic theory).

In eukaryotes, the ribosomes may be classified as either ‘free’ or ‘bound’. Free ribosomes may be found suspended in the cytosol whereas bound ribosomes are attached to endoplasmic reticulum (as such called rough endoplasmic reticulum). Free ribosomes are involved in the synthesis of proteins that will function in the cytosol while bound ribosomes in the synthesis of proteins that are to be exported or used within the cell membrane. The two types of ribosomes have similar function and structure, and in fact, are interchangeable.

Word origin: from ribonucleic acid and Greek: soma (meaning body).

Related forms: ribosomal (adjective).
Related terms: ribosome binding site, ribosome-lamella complex.

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Re: Why is ATP rather than GTP, CTP or TTP the energy currency?

The above reply is very interesting, thank you! I have wondered for a while what drives protein synthesis forward in terms of energy, and why don't ribosomes also catalyse the reverse reaction of peptide formation, now I guess it's due to the GTP hydrolysis? But I also have some questions about ...

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by Maus
Tue Feb 03, 2015 6:46 pm
Forum: Molecular Biology
Topic: Why is ATP rather than GTP, CTP or TTP the energy currency?
Replies: 6
Views: 9517

Re: Totipotent Stem Cell From Molecular Components

... in # of strands of mRNA * 100. I am getting the protein this way. I take the results of PCR and put it in a test tube with RNA polymerases, Ribosomes, and other proteins that help with protein synthesis. I then look at the structure of the protein as is and inside a cell(every single bond) ...

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by caters
Fri Aug 01, 2014 1:42 am
Forum: Cell Biology
Topic: Totipotent Stem Cell From Molecular Components
Replies: 2
Views: 6843

Living or not? (viruses,viroids and prions).

... cell. http://www.atsu.edu/faculty/chamberlain/Website/Lects/Rickett.htm They need to get their ATP from other cells, but they still have their own ribosomes (unlike mimivirus). That makes them heterotrophs, but not viruses. Furthermore, they have membranes, not mere envelopes. But, considering ...

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by wildfunguy
Thu Oct 17, 2013 10:20 pm
Forum: Microbiology
Topic: Living or not? (viruses,viroids and prions).
Replies: 15
Views: 17981

Re: Why is ATP rather than GTP, CTP or TTP the energy currency?

... is the ATP preferred energy currency MOST OF THE TIME , BUT “ NOT ALL OF THE TIME” : GTP is primarily used for Protein synthesis at the ribosomes . GTP hydrolysis is SLOW .* The extra amount of time prior to GTP hydrolysis (Compared to ATP) allows `the final fidelity check` to take place.Faster ...

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by metingun2
Sun Oct 06, 2013 11:53 am
Forum: Molecular Biology
Topic: Why is ATP rather than GTP, CTP or TTP the energy currency?
Replies: 6
Views: 9517


you neglected about ribosomes flagella and cillia found in prokaryotes !

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by adithya528
Thu Sep 12, 2013 5:41 pm
Forum: Cell Biology
Topic: prokartotes
Replies: 4
Views: 3638
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