How does a cell know what it is supposed to be?

Question

It has something to do with differentiation. I have found many sites stating why... but they all just confuse me =S

HOW exactly do they know... there is a specific way. I talked to my Biology teacher about it and he said there was a specific reason... they don't just know...

Answer 1

This is a great great question. The question is how can a single fertilized egg cell go from this zygote, to all these differentiated cell types, and organs, and connective tissue, etc. Well, embryologic development is a very complex, but I will try to give you a very simplified explanation.

So, as the zygote divides from 1 cell to 2 cells to 4 cells to 8 cells, and starts to form a ball of cells (called a blastocyst), these cells constitutively express certain transcription factors called homeodomains. So if all of these cells express these homeodomains, and the molecules can be transported into and out of cells, think about how much of the transcription factor will be present in each cell. The amount will be different in the cells located in different places! The outside of the blastocyst has fewer neighboring cells relative to the inside, so the amount of transcription factor present in the outside cells will be less than the inside cells. This has created a GRADIENT of these transcription factors, and this will lead to different concentrations of protein product in different parts of the blastocyst.

Some of the genes that work in embrylogic development are HOX genes, and the very important sonic hedgehog gene. But this is just a simplified explanation of how cells become differentiated at the beginning of development.

Answer 2

It is an amazing process of differentiation. There are signals that turn on and off, almost like a red light/green light. You start with a fertilized egg and after a dozen or so divisions you have a ball of cells that all look pretty much the same. The ball keeps growing into a hollow ball and along the"spine" a fold grows. This goes on to become the head, and spinal cord and gut....This is where tissues are differentiating like crazy. There are signals from the DNA turning on some proteins and turning off others. Cells can tell what kind of cell they are located next to. They do this with membrane proteins. Cells also migrate. They can move into other tissues and form different parts there.
I know this is a really general explanation, but there is so much going on and it is very complicated. Look into "early embryology". That might help. Good luck.

Answer 3

Stem cells don't,the ones in the placenta and umbilical cord.
Once they are assigned to their spot they know if they have to be a finger or a heart..
DNA specifies their assignment.