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Ribosomes :S

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    Hello,

    I'm a bit confused as to what the differences are between 40S and 60S ribosomes.
    Also, why are they kept separated in the nucleus? :holmes:

    Thanks.
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    If only they had been 6S and 7S ribosomes.
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    (Original post by M1F2R3)
    If only they had been 6S and 7S ribosomes.
    Damn eukaryotes. :cry2:
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    (Original post by hollywoodbudgie)
    Damn eukaryotes. :cry2:
    Damn right
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    On a serious note, it was a long time since I did A level biology... Don't the 40S and 60S come as a result of the 80S releasing the subunits?
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    Eukaryotes have 80S ribosomes consisting of a small (40S) and large (60S) subunits. I'm pretty sure ribosomes don't enter the nucleus :confused: the rRNA is produced in the nucleus but is exported and combines with the ribonucleoproteins in the cytoplasm.
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    (Original post by M1F2R3)
    On a serious note, it was a long time since I did A level biology... Don't the 40S and 60S come as a result of the 80S releasing the subunits?
    I'm a university student. :sad:

    (Original post by Philbert)
    Eukaryotes have 80S ribosomes consisting of a small (40S) and large (60S) subunits. I'm pretty sure ribosomes don't enter the nucleus :confused: the rRNA is produced in the nucleus but is exported and combines with the ribonucleoproteins in the cytoplasm.
    Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit.
    The subunits of ribosomes are produced in the nucleolus, (but they combine in the cytoplasm).
    Erm so is the difference between 40S and 60S just the size?
    (It doesn't explain why they're kept apart though).
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    (Original post by hollywoodbudgie)
    Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit.
    The subunits of ribosomes are produced in the nucleolus, (but they combine in the cytoplasm).
    Erm so is the difference between 40S and 60S just the size?
    (It doesn't explain why they're kept apart though).
    The rRNA is produced in the nucleus, the protein component of ribosomes in made from mRNA in the cytoplasm. There are also difference in the sizes of the rRNA, and they have different roles. During translation, the mRNA binds to the small subunit and the complex comes together. The tRNA binding sites are formed from the interface of the small and large subunits.

    I don't understand what you mean by kept apart. You mean in the cytoplasm? They just float around until a mRNA binds to a 40S subunit and the complex is formed.
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    (Original post by Philbert)
    The rRNA is produced in the nucleus, the protein component of ribosomes in made from mRNA in the cytoplasm. There are also difference in the sizes of the rRNA, and they have different roles. During translation, the mRNA binds to the small subunit and the complex comes together. The tRNA binding sites are formed from the interface of the small and large subunits.

    I don't understand what you mean by kept apart. You mean in the cytoplasm? They just float around until a mRNA binds to a 40S subunit and the complex is formed.
    This is one of my lecture slides:



    It asks that question and shows the 40S and 60S subunit being put together in the nucelous. :puppyeyes:
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    Bump?
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    (Original post by hollywoodbudgie)
    This is one of my lecture slides:
    It asks that question and shows the 40S and 60S subunit being put together in the nucelous. :puppyeyes:
    I have no idea. To be honest, I have never covered this, we only learnt about the structure of ribosomes and their role in transcription. It appears I was quite wrong about some things.

    Was this not addressed in the lecture? Have you looked at the paper this diagram came from? If the answer isn't there, ask your lecturer.
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    Thanks for the help anyway
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    (Original post by hollywoodbudgie)
    Thanks for the help anyway
    No problem Sorry I couldn't help more. I hope you find the answer.

    Oh, and cheers for the rep.
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    complete and total guess - as in, I know almost nothing about cell biology - but perhaps to keep them inactive until they're in the right environment (cytoplasm) not to mess anything else up? otherwise they might spontaneously start transcribing in the nucleus and might mess everything up..?
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    Yeah i'd guess that either its to prevent protein synthesis happening in the nucleus or possibly its just because that's the way it works?

    (Original post by hollywoodbudgie)
    It asks that question and shows the 40S and 60S subunit being put together in the nucelous. :puppyeyes:
    Yes - in the experiment illustrated in that picture they show that ribosomes are created in the nucleolus by tagging ribosomal proteins with GFP. The proteins enter the nucleus, form all those pre-complexes such as the 90S pre-complex (not a ribosome), then exit the cell as two separate functional units. Is there a problem with that? :confused:
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    (Original post by hollywoodbudgie)
    Hello,

    I'm a bit confused as to what the differences are between 40S and 60S ribosomes.
    Also, why are they kept separated in the nucleus? :holmes:

    Thanks.
    Hehe that diagram is Fannis!! Hi!
    So have you figured it out? I have no idea myself
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    (Original post by hollywoodbudgie)
    This is one of my lecture slides:



    It asks that question and shows the 40S and 60S subunit being put together in the nucelous. :puppyeyes:
    I would think are a multitude of reasons why the system has evolved in this manner, as stated above, translational processes taking place within the nucleus could have profound and devastating effects on gene regulation, cell signalling etc. Many cell processes depend on the compartmentalisation within cells and upon there being a difference in the protein content of each compartment. Even so, the ribosomal subunits are kept separate within the cytoplasm anyway as individual units, and only come together upon the initiation of translation.

    The 'S' part of 40S/60S refers to the proteins Svedburg value which is a unit that describes the sedimentation coefficient. It's usually expressed in time, and sort-of refers to the time required for a particle to sediment during centrifugation. This rate depends on many things like size, shape etc. but in general the bigger a particle is, the faster it will sediment thus 60S is a bigger protein then 40S

    As you can see from the diagram, the 90S ribonucleoprotein is cleaved into the pre-60S and pre-40S subunits, which along with various factors undergo additional processing and are exported into the cytoplasm. It is thought that the pre-60S subunit requires further processing in the cytoplasm before it is even biologically active. This may also be true for the 40S subunit. This may act as a second fail-safe to ensure translation does not take place in the nucleus!
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    The horror when one encounters a Fanis Missirlis lecture slide. I don't think this one has enough traffic lights though?

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Updated: May 14, 2012
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