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Animal cell nucleus shape changes

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Animal cell nucleus shape changes

Postby ericjoe » Sun Nov 11, 2012 12:04 pm

Hi, I have a doubt regarding nucleus shape.

Can anyone verify the statement below with my questions
"Except during cell division, the nucleus appears amorphous".


From the statement and my understanding of amorphous (without a clearly defined shape)
1) Is the nucleus shape unregulated most of the time?
2) Why the nucleus shape is not amorphous (means the nucleus shape is fixed) during cell division?

I have tried to google "nucleus shape fixed cell division", but I could not get a satisfying explanation.

Hope you may help to explain the statement above and thank you in advance.
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Postby biohazard » Mon Nov 12, 2012 10:17 am

Most cells have a well-defined nucleus especially when not in cell division. So, in my opinion that statement is false. Or at least poorly defined. Under a light microscope in a native sample the nucleus may "appear" amorphous, but it is not so in reality.

1) The shape of the nucleus is always regulated, as far as I know. During mitosis the nucleus is disintegrated for a period of time, in a controlled manner.
2) During cell division there is a phase (from prometaphase onwards) where one could perhaps describe the nucleus to be amorphous, as it has no defined shape.

That statement would thus correctly describe the nucleus during cell division.

May I ask where that statement is from or who said it? A textbook? A teacher? And in what context?
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Postby ericjoe » Mon Nov 12, 2012 1:44 pm

Hmm from your explanation, can I assume that:

1) Nucleus shape is not fixed, it changes during cell division (mitosis).
2) Under normal condition (not during cell division), the nucleus shape remains fixed.

I got this sentence from a lecture slide. It is very simplified and the lecturer who wrote this has long retired from my college. That is why I have to post a question here.

If you are interested, I can quote my lecture slides. It is not long, just a few lines in fact.

Thank you for your feedback.
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Postby biohazard » Mon Nov 12, 2012 2:04 pm

Yeah, I think you can make those two assumptions. Although there are exceptions to this rule as well, like there are exceptions to almost everything in biology.

For example, in many cells the nucleus also changes in shape when the cell matures. This is well evident in, for example, neutrophilic leukocytes whose nuclei become lobular and very irregular-shaped during the cell maturation (but still follows a defined and controlled pathway). Another good example is the red blood cell, who has a nucleus in immature stages (erythroblast) but completely loses it when it becomes a mature erythrocyte.

Thus, the nucleus shape is typically "fixed" only in resting, mature cells. When the cell activates, for meiosis or for other reasons, the shape often changes. But in almost all cases the nucleus shape is well-defined and the changes are strictly controlled. So perhaps a better term would be "dynamic, but defined", which is almost the same as "fixed" if the cell is mature and/or inactive.

Mitosis is a little peculiar case, since during it the nuclear membrane briefly disappears and is re-assmbled for both of the daughter cells after the new chromatin molecules have been delivered to their correct destinations. And in my opinion, for most cells cell division is the only stage when the nucleus can be said to be "amorphous", as expressed in the original statement.

And the above applies only to animal cells (like mentioned in the thread topic), other organisms do things differently, again.

Oh, and feel free to quote those slides. I can try to figure out what that statement is actually trying to tell us.
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Re: Animal cell nucleus shape changes

Postby jonmoulton » Mon Nov 12, 2012 4:34 pm

There are some genetic conditions that can affect nuclear membrane shape, in particular the laminopathy that causes Hutchinson-Gilford progeria. See figure 1 in the following paper for some nuclear membrane images:

Scaffidi P, Gordon L, Misteli T (2005) The cell nucleus and aging: Tantalizing clues and hopeful
promises. PLoS Biol 3(11): e395.

http://www.plosbiology.org/article/info ... io.0030395
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Re: Animal cell nucleus shape changes

Postby andrewpasha » Fri Nov 16, 2012 2:59 pm

In most of the Eukaryotic cells the nucleus has role as a characteristic feature. There is a double membrane around the nucleus and it contains chromatin material. So nucleus is an important part of Eukaryotic cells because it stores genetic information. During the cell division e.g. in mitosis and meiosis nucleus play important role. The process of Translation and the transcription are also occurring in it. Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. As the cell prepares to divide i.e. enters mitosis or meiosis. Chromatin packages more tightly to facilitate segregation of the chromosomes during anaphase.
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Re: Animal cell nucleus shape changes

Postby jonmoulton » Fri Nov 16, 2012 4:03 pm

That's a good shot at a summary, Andrewpasha. There are a few errors; understand that I am applauding your effort and hope to help you sharpen your next project. First, a major role of the nucleus during cell division is to temporarily get out of the way; the nuclear membrane disappears for a while. Transcription occurs in the nucleus, but then the mRNA is moved out of the nucleus to the cytosol where translation takes place. Chromatin is an important part of the contents of the nucleus, but other structures (for instance splicosomes) are also present and vital for gene expression. You are tackling an important topic, common to all large organisms; please accept my critical reading and feedback in the friendly spirit in which I offer it, and do continue your writing.
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Re: Animal cell nucleus shape changes

Postby andrewpasha » Tue Nov 20, 2012 3:37 pm

Thanks for guiding me. It’s very good for me. Now I understand about the Transcription and movement of mRNA. I want to share something about centrifuge.

Centrifuge is a machine that is use to rotate an object around a fixed axis and during this circular motion the acceleration is the product of radius and the square of angular velocity . If the acceleration is gravitational acceleration then it known as relative centrifugal force.
It can be write as

RCF = rw2/g
where
= angular velocity

= rotational radius
g = Gravitational acceleration



The Centrifugal separation methods are of three types
Differential pelleting
Rate zonal centrifugation
Isopycnic centrifugation
In differential pelleting a sample is subjected to centrifugal separation to allow particles to sediment.
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