• Question: Why have white blood cells got such a large nucleus and such a small cytoplasm?

    Asked by 08sanah to Cat, Daz, Holly, Johnson, Pamela on 17 Jun 2011.
    • Photo: Darren Braddick

      Darren Braddick answered on 16 Jun 2011:

      Hi 08sanah

      White blood cells work in your immune system. The immune system has two main parts, one is called innate, and is basically a simple and nonspecific, aggressive response, and the other is called adaptive, and this is much more specific. The adaptive immune system works because it makes small proteins (antibodies) which can recognise the shape of thousands and thousands and thousands of bad molecules – like bacteria, viruses, toxins, and many others. The reason for the large nucleus is probably because all of the proteins that the white blood cell needs to do its work is very big. All proteins are made from specific DNA sequences – which in turn means there must be a lot of DNA, and a lot of protein synthesis from that DNA!

      I’ve made this process quite simple and skipped some important steps, but I think that the size and function of the DNA in the white blood cell is the reason for the particular shape of its nucleus.

      I hope that helps.. I may not be completely right on this though!

      Daz

    • Photo: Pamela Lithgow

      Pamela Lithgow answered on 16 Jun 2011:

      Hi 08sanah,
      I’m sorry Daz but if I am understanding what you wrote I think you might have got it a bit wrong. I think you are saying that the white blood cell nucleus is bigger because it has more DNA in it to do more things, is that what you said? If not I am sorry. But all cells in animals have the same amount of DNA, that’s why they can get your DNA from a hair or from a mouth swab to compare to stuff at crime scenes (all very CSI). The truth is that most animal cells actually have a nucleus that is about the same size. What happens is that you look at different picture where the cytoplasm and nucleus take up different amounts and that can make the nucleus look bigger but it just because the pictures are not on the same scale. This is not the same for things like bacteria where different bacteria strains with different amounts of genes do have different sizes of nucleus.
      So what really changes is the amount of cytoplasm as you said, if you think of the cytoplasm as a factory then what the cell needs to produce decides how big the factory/cytoplasm needs to be! So the cells which you describe as small with big nucleus are like this because they don’t need to produce much.
      However, I would like to say that “white blood cells” are made up of different types of cells with different amounts of cytoplasm. T and B cells are as you describe small cells with what looks like they have a large nucleus they are like this as it is what they need to do what they need to. (These cells can expand their cytoplasm if they need to produce more stuff though!). Another type of white blood cells are the large granular cells which include NK cells and macrophages (which I work on) which have quite big nucleus and lots of cytoplasm. In their cytoplasm they have lots of granules (thus the name!) and they need these to perform their functions.
      So in answer to your question the amount of cytoplasm is dependent on the function of the cell and the nucleus actually stays the same size.
      I know that is a slightly complicated answer but it is quite a complicated question!! Please comment if you would like me to clarify anything!
      Hope that helps
      Pam 🙂

    • Photo: Cat O'Connor

      Cat O'Connor answered on 17 Jun 2011:

      Hi 08sanah,

      I think Daz and Pam are giving you enough information to get your head around so i’m not going to add to it ;D

      Cat

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