How do cells know to become a heart or a brain or other body parts?

Question

If they all have the same DNA, how do they figure out what to become

Answer 1

Good question. We actually do know how it happens. There are a lot of different methods, and they are very complicated, but I'll try to outline it a little.

The main method has to do with gradients. The simplest and most studied model is the fruit fly. When the egg is still a clump of cells, cells at one end will begin secreting growth factors (proteins that tell the cells what to do), lets say Growth Factor A. The cells at the other end of the cell will start secreting Growth Factor B. Cells in the exact center of the embryo will 'see' an equal concentration of A and B. Cells closer to side A, will see more GF A and less GF B, and vice versa. Cells then begin to differentiate based on what concentrations of growth factors they are exposed to, and some begin to secrete growth factors of their own.

When a mammalian egg is fertilized, it begins dividing, and implants into the wall of the uterus. The uterus secretes growth factors . The ball of cells then has a reference point, i.e. the direction with the highest growth factor concentration is 'down.'

Over time, the ball of cells folds inwards, and cells flood inside. They are exposed to different signals based on which part of the embryo they flowed over, and then begin to secrete signals of their own. The DNA of the cells is mostly the same (some genes are still present but 'silenced' in certain cell types). For the most part, the DNA tells the cells how to react to growth factors, and how to maintain its internal machinery, but doesn't provide detailed information on how a cell should differentiate and where it should wind up.

Have you ever played a game where you're given a clue to find a location where a second clue is hidden, leading to a third, and so on? It's kind of like that, but highly branched and orders of magnitude more complex. It's as if someone left clues for you all over the country, and each clue could lead to a hundred different clues, based on what clues you had seen before and the locations of other players in the game.

It's all an incredibly complex and perfectly orchestrated chain reaction of frequently-changing signals, and even small errors can lead to extreme abnormalities, such as a lack of limbs (or extra or malformed limbs), brain abnormalities, and so on.

Answer 2

we have no idea..scientists are trying to find this out every single day...the one that finally figures it out will become a very rich man/woman