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Friday, May 25, 2007

Development

Okay, so I know most of the people visiting this blog find biology awfully boring.
Well I can't seem to complain given that I hated it too during school. Anyway lets put all that behind and try to make things interesting.

Now Twish had some really interesting posts which definitely might have made all of you think about the brain in terms of circuits, processing, perception and a whole lot of other things. However before I put up a post about the workings of the brain, I have to first get everyone to know how the brain or for that matter any organ develops. (wait, it doesn't start getting boring here, I am gonna talk about circuits in a totally different way).

So lets start with two cells i.e the resultant of the fusion of the sperm and the ovum. So what happens next. How is it determined which cells become what in the course of division of these two cells to form the millions of cells that is us? How is it that the neurons are formed only in the brain and the spinal cord and other regions? What makes the heart not be in the place of the kidneys and the blood cells to be as they are? (No, this is something that isn't easily ascribed to the creations of a higher power namely God)

So what happens is a completely different branch of biology that is called Developmental Biology.
I can't promise you that I shall give you the answers to what makes the heart cells to not become neurons and vice versa but what I can say is that probably some of you might see the analogy between genetics and circuits.

So now lets get to the start of development. You have 2 cells and they divide something like 9 times over. Till this point none of the cells are in anyway different from one another (or atleast no one has been able to prove that they are). So these cells are called embryonic stem cells (ESC). Now once this stage has been reached what happens is that the embryo starts getting polarised, by polarised I mean to say that now you have distinct regions within the embryo which you can differentiate. Hence we now have an anterior (mouth) end and a posterior (anus) end. Similarly we have left and right sides and up and down distinctions.

But in turn how do two cells differ simply becuase of positions. This is due to a clever trick brought about by diffusion of protein products that have been passed on with the ovum(the sperm is a poor guy who contributes only DNA and no proteins).

So how do these circuits work?
Due to the proteins passed into the embryo by the ovum, these protein create a gradient by simple diffusion and the varying levels of these proteins at different areas "switch on" or "switch off" certain specific genes and these genes form certain other proteins and so on and so forth. Now the products of these genes are important for the activity of other genes and so forth. Thus what you have is a series of AND/IF/OR gates which function together in a highly complexical manner leading to different cells showing different reactions to the same stimulus.

Thus in most simple words, this is the basis of differentiation of cells to form neurons and muscle cells and liver cells.



I think this much is enough at one go, shall write more once I feel it has been adequately understood.

4 comments:

obiwankenoby said...

dear nav! shake off any reservations you have about us not liking biology. i can say for myself that i loved biology--but i loved maths more--thats all. and if i had a teach like you i m not sure if i would hav gone over for maths in the first place.
you do make it interesting and the article is shaping up very well.


to others-- i had been absent for the last few days as i had gone home to get treated for a pain in the right shoulder - compressive milopathy is what i have, and my spine is a little deformed due to my sit-and-read-posture.
my father is trying to turn me over to baba ramdev and i have gallantly thwarted the attempt once again!
and i am going to post soon (note "soon") and i want to.
prof dattagupta has assigned us mechanics from landau and its dutch to me.
so i am referencing langrangian mechanics and its like a whole new apprach to seeing things.
right bye.

Arun Chaganty said...

I too have the same outlook as obiwan, I *love* biology, atleast most aspects of it

Amazing article! I'm stunned by the way our body does its stuff! I mean logic circuits?!! I believe cell differentiation is one of the greatest problems in biology.

Now, you've explained everything so well, I can't really think of any questions I'd like to ask.

I actually though of asking something, but it's quite clear that it has been covered. What I was going to as is: How do the cells and the protein gradient line up? I'm figuring that they don't need to line-up. The cells are all the same, until the protien gradient differentiates them.

Could you give a little more elaboration on the AND/OR/NOT logic gate action of it? I'm just amazed by it. I do remember a Resonance article about circuits in the Cell.


Also, I have an unconnected, longstanding question, since my school days (my teach also didn't know). How are the genes realised? I mean genes are traits (abstract) that are found in DNA. How are the chromosones related to the DNA and the genes? Is it like 10 bases a gene, or is that not set? Is there a clear way of telling which genes are where in the genome sequence?

Navneet said...

@obi: thanks for the praise, you're just too kind :)

@arun: will have to take up the gates thing in a separate post.

about the genes...a gene isn't an abstract concept...a gene can be quite well defined...look it up on wiki.
so in higher organisms such as us...the total genetic material is divided unequally in the form of chromosomes...so each chromosome has a defined no. of genes on it.

since we've now sequenced the human genome...scientists are able to very well specify locations of specific genes as well as find newer ones hitherto unknown

hope this satisfies you

Arun Chaganty said...

Ah, thanks. I should have done that first. For those too lazy to look (i.e. people like me), the answer is that the gene size is very different, between 40 base pairs, to 10000's. For us (homo sapiens), it's about 14 genes per million base pairs.

I was quite startled to find that the current definition of "gene" is radically different from what I learnt in school.