• Question: Do cells reproduce? If not, how do we get a constant refill of cells once they die?

    Asked by pranay900 to Alexis, Dr D, Helen, Jasmine, Mario on 24 Jun 2013.
    • Photo: Andrew Devitt

      Andrew Devitt answered on 24 Jun 2013:

      This is a good question but the answer isn’t simple.

      Some cells divide and make more of themselves – so B cells that make antibodies, divide to make more B cells. Some will live to balance those that die. But some cells don’t divide so to get more of them, we need an immature version or stem cells to make new ones. So macrophages don’t divide. They get formed fresh when we need more – these come from a blood cell called a monocyte.

      But then there are cells that don’t divide and aren’t easily replaced – like nerve cell – so look after your spine!

    • Photo: Mario Ruiz

      Mario Ruiz answered on 24 Jun 2013:

      They do! Cell division is the main process of cell reproduction, since one cell becomes two. Also, stem cells can be transformed in any cell type, and those are being produced by division too. Even if millions of cells die in our bodies (no matter where), other millions divide and replace the ones that pass away

    • Photo: Alexis Barr

      Alexis Barr answered on 24 Jun 2013:

      Cells do reproduce, but not all of them. As you develop all your cells reproduce so your organs can grow to their adult size. As an adult, many cells stop reproducing and instead do the job they are designed to do – like nerve cells, as Andrew said. BUT as an adult you’re exactly right that we need to refill cells that die. So your blood cells are constantly reproducing. Red blood cells only hang around for about 100 days and so they have to be replaced from stem cells in the bone marrow – about 2 million per second are produced in an adult!
      Your skin cells are another type of cell that are constantly being replaced. The skin you see is basically dead cells that are constantly being shed off your skin (making your house very dusty).

Comments

  • Photo: adamrutherford

    adamrutherford commented on :

    Hello, what an excellent question. What you’re asking is basically one of the pillars of biology. We have three ‘Grand Unifying Theories’ in biology (physicists have been trying to come up with one for hundreds of years: in your face, physics!), which describe everything about living things. Genetics is one, the fact that all life is encoded by DNA, using the same code, letters, alphabet and language. Then there’s Darwin’s theory of evolution by natural selection: the idea that all species have evolved from a common ancestor by this process of trial and error (or rather error then trial). But the first Grand Unifying law of biology was ‘Cell Theory’. Quite simply it states that
    1) All life is made of cells
    2) Cells can only come from existing cells.
    It was worked out in the 19th century by a whole crew of European scientists (and yes there are some complications, as ever in science: viruses are generally considered to be not alive as they need to hijack living cells to reproduce themselves).
    But in general it’s really a cornerstone of biology that cells reproduce because every cell that has ever existed must have come from one that came before it. Now, there are hundreds of types of cells in your body, making up around 50 Trillion. You started as a single cell, but due to an extremely well-coordinated combination of your genes and your environment, that has reproduced billions of times and changed each of those cells in to specific types: basically so you have eye cells in your eyes, and stomach cell in your stomach. The other way round would be bad. You also carry probably 500 trillion cells that are not human (bacteria, yeast, other stuff: much essential to healthy living). But every one of them was born from an existing cell, as those ones were, as their parents were etc etc etc, right the way back to the origin of life itself, which was the formation of the very first cell, which we call Luca (the Last Universal Common Ancestor). That, I reckon, is the most amazing thing about biology: every single cell in your body has an ancestry that is 4 billion years old.
    Now, as Andrew, Mario and Alexis say above, not all cells naturally reproduce. Brain cells in general don’t. Red Blood Cells make up about a third of all your cells don’t contain any DNA, so can’t reproduce. But in recent years, scientists have really begun to unravel how cells work, and are beginning to change cells from one type to another, and to get cells to reproduce that otherwise wouldn’t./ This might be extremely useful in the future for treat things like brain diseases, like Alzheimer’s, were the brain cells die, and can’t be replaced.
    So, basically: cells do reproduce and this is one of the most important aspects to all life there is. The ones that don’t, we’re trying to work out how to change that to help treat diseases.