Question

How dome some cells become brain cells and others become skin cells, when the DNA in all the cells is exactly the same. In other words, if the instruction are exactly the same, how does one cell become a brain cell and another a skin cell?

Answer 1

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moving on to ur ques..thats really a nice ques....see even though the DNA is same in every cell it is packed differently....ie in some cells maybe A B C D genes are packed tightly so they cannot be accessed to undergo transcription...but the other genes can be accessed so it maybe become a hepatocyte in other A B C D not tightly packed so it may take different morphology. this packing is called heterochromatin(tightly packed and cannot be accessed) and euchromatin(loosely packed and can be accessed)

Answer 2

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Answer 3

shruti pande9 is right . The scientific term for this process is " EPIGENETICS ".

genetics is defined as changes in gene expression mediated by alterations in DNA sequence eg mutations.

Epigenetics means changes in gene expression mediated by alterations in the way chromatin is packaged within the nucleus. In this process there is no change in DNA sequence at all.

For any gene to be expressed , its promoter region must be bound by a transcription factor. But if the promoter of the gene is tightly packaged into heterochromatin , it wont be be available for transcription factor binding and thus wont express. In other words we can say that the gene has been switched " off ". The opposite will happen for the gene to be switched "on"

All you differentiated cells like skin cells and neurons come from undifferentiated stem cells. So as stem cells divide and differentiate into skin cells , the genes responsible for neuron/ any other cell type formation are switched " off " by their tight packaging whereas genes for skin cell formation are switched "on " by unwinding of DNA in regions where genes specifying skin cell formation are present.

Kindly go through the attached image , part b for a better understanding.