The Core
CHANGING CELL TYPE
Some biologists love feedback loops and study how they are connected in huge networks in cells, a bit like electrical circuits
This area of science is called Systems Biology
Stem cell = cell that can turn into many different kinds of cells
Differentiated cell = a specific kind of cell that fulfils a specific purpose.
In THE CORE, we've covered 3 processes which are central to biology:
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Transcription
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Translation
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Cell division
Each of these three processes, along with most other things a cell does, are controlled and carried out by proteins.
So, not only are proteins essential for cell shape and equipment, they are essential to control which proteins are made in the first place via transcription and translation. As you can imagine, this can easily result in a positive feedback loop: protein A promotes the transcription and translation of more protein A, which makes even more protein A, etc..
As you can imagine, when you start getting into a positive feedback loop, it can be difficult to get out of it.
One example of where positive feedback loops like this are important is cell differentiation. Cell differentiation is the process by which a stem cell turns into a specific cell type or differentiated cell e.g. a lung cell.
Here a stem cell is differentiating into a lung cell.
At the beginning, this stem cell will be full of stem-cell-specific proteins. During this process, one lung-cell-specific protein could be made, and if its part of a positive feedback loop it can start making lots of lung-cell-specific proteins, and eventually this makes the cell full of proteins that you find only in lung cells.
The positive feedback loop keeps the cell a lung cell, so it's very difficult to turn it back to a stem cell.