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How do Cells "think"...

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How do Cells "think"...

Postby lenfromkits » Sun Nov 22, 2009 8:49 pm

Hi. There is obviously an abundance of discussion about how cells are able to determine what type of cell they are to become (differentiation), however, there is very little talk about how cells are able to respond to their environment.

If you consider how a white blood cell (phagocyte) is able to attack a pathogen (see this great video: http://www.youtube.com/watch?v=ZLoJG5gq ... r_embedded ), CLEARLY the cell is able to do the following - in a VERY sophisticated way:

- Observe details of its environment (input)
- Process information and make decisions (thinking)
- Respond by directing the actions the cell (output)

How does a cell do all this when a cell obviously does not have a nervous system or any ability to 'think?' This type of function normally could only be done if the organism had a nervous system.
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Postby canalon » Mon Nov 23, 2009 2:22 am

Chemotaxis could be involved, and does not involve thinking, just a positive feedback within a chemical gradient.
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Postby kolean » Mon Nov 23, 2009 3:12 am

Just curious, how do you think we "think"? From your answer it seems that it is the nervous system. What is a nervous system composed of? Cells. Thus we "think" with our cells (albeit a composite of many different types of cells).
Chemotaxis is one way, but it all has to do with biochemicals and their reactions. Interaction with the environment is usually by cell signaling (ligands and receptors) and the cascade of reactions that follow.
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Re: How do Cells "think"...

Postby lenfromkits » Mon Nov 23, 2009 6:11 am

I am generalizing "thinking" to be just the process of "adding meaningful changes to an input before delivering the output."

I am reading a lot of information about "receptors" (inputs) and about "chemotaxis" (outputs) but not a lot about what happens in between. I do see a lot of research results of the "in between" part immediately at one side or the other (ie, details of how the receptors work or details about the mechanisms that a cell uses to move), but I don't see much joining the inputs to the outputs, especially for higher organisms like white blood cells.

The best I have found are comments like "In more advanced systems, such as the active movement of a eukaryotic cell towards a particular chemical agent, this response certainly must be a result of a series of complex biological steps." (http://www.ncbi.nlm.nih.gov/pmc/article ... 66/?page=6)

It seems to me that life often finds one way or another to manage itself in its environment - via receptors, information-processing and then responses and that evolution has developed these same functions in more than one way. Complex multi-cellular organisms do it via a nervous system whereas single cells have an entirely unique method that we have yet to fully identify.

My main objective in asking this question is to simply find out if there is a missing link there that we are still trying to find an answer for. I would like to know if this mystery still exists (which includes the mystery of how a cell knows whether it is to become a toe nail cell or a liver cell).
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Postby kolean » Mon Nov 23, 2009 6:40 pm

lenfromkits wrote:how a cell knows whether it is to become a toe nail cell or a liver cell).

Cellular differentiation defines what the cell is to be. Transcription factors are turned on for that particular cell, while others are turned off.

How a cell expresses what genes and not other genes, is called epigenetics (which I have been researching for half a year already and still have so much more to learn). Alot of research has exploded on the scene about chromatin remodeling and DNA methylations that seem to be another layer of regulation of gene expression, and thus differentiation. Because you have to remember that all the DNA in a cell is the same for all the cells (a liver cell and the toe nail cell), but some cells have genes that are repressed while the others are expressed.

If you want to know more about what is in between input and delivering output, I would look at signaling cascades then. MAPK is a good one or for a generalized one:
http://en.wikipedia.org/wiki/Cell_signaling
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Re: How do Cells "think"...

Postby lenfromkits » Tue Nov 24, 2009 1:27 am

Thank you, Kolean.

You have provided exactly what I was looking for. "Signalling" led me to "Systems Biology" and ideas about emerging properties, etc, which was exactly what I was after. I have now verified a theory on this related to evolution and can proceed with my paper.

Thanks!

Len
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Postby mith » Wed Nov 25, 2009 7:47 pm

There's a recent systems bio paper on chemotaxis
http://www.pnas.org/content/97/9/4649.full

basically an error signal is produced by the sensors that is integrated by a controller and outputted to the actuator (flagella motor).

The network has about as much thought as a thermostat would have in keeping an oven at a "steady" temperature.

edit: the above paper is more interested in the mechanism of the network, the network itself is talked about in the barkai paper.
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Re: How do Cells "think"...

Postby lenfromkits » Sat Nov 28, 2009 12:26 am

Hi Mith,

Thanks for the link to http://www.pnas.org/content/97/9/4649.full.

I had a good look at this document and putting in terms of your analogy, this document only focuses on the thermostat itself, not the furnace. The 'feedback' they are discussing is within the thermostat itself to make it more sensitive to 'changing' temperature. So the analogy doesn't really apply either because thermostats only care about the static temperature.

A better analogy would be if we needed to know if the temperature was rising steadily (pretend that could mean some sort of danger). The "feedback" that the refer to allows the thermometer to "detect that the temperature has risen" - then reset itself so that the current temperature is "now the norm and forget that it had previously risen" so that it is ready to again detect a further increase. The 'feedback' refers to the part where the thermostat adapts/desensitizes (ie, in psych referred to has habituation) to the existing 'change' so that it is ready to detect another change.

So, we still do not have much on the topic of what connects this thermometer to the furnace. My analogy of this is when using a 'beacon' to search for a lost person in the snow where the beacon can only tell you if you're (sort of) getting closer. My brain still connects the readings of the receptor (beacon/eyes) to my legs.
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