Thread: How does DNA know what type of cell to make?

If DNA is the blueprint for making proteins which are used to make the cells, then how does DNA "know" which proteins to make for the certain type of cell (bone, skin, muscle, etc.) it is creating? Is this started by the reproductive organs of the parent telling embryonic stem cells what to do in the beginning, and then those just making that same type of cell over and over again? Or is this something that the embryo's own DNA tells them to do with no outside influence?

Considering the stem cells itself, it is currently in research, so I can't tell you much about it.

Speaking of replication, however, as you probably know, DNA is formed of 4 types of nucleotides, namely adenine, thymine, cytosine, and guanine. In short, ATCG. When there is a need for a new protein, the messenger RNA comes to the DNA and makes an exact opposite of the three nucleotides forming a codone. Often, more then one codone is needed to create a specific amino acid. For example, the lysine amino acid on the DNA is marked with the chain of amino acids going like: TTT TTC. When the mRNA comes, it forms a chain going like: AAA AAG. Than, it goes to the rRNA and there it creates a specific amino acid from the code, in this case, lysine. The process is repeated until the mRNA reaches a stop codone, for instance UGA (thymine exists only in DNA, in RNA it is replaced with uracil.). At that time, all of the amino acids for a protein have been created.

Originally Posted by mobc

If DNA is the blueprint for making proteins which are used to make the cells, then how does DNA "know" which proteins to make for the certain type of cell (bone, skin, muscle, etc.) it is creating? Is this started by the reproductive organs of the parent telling embryonic stem cells what to do in the beginning, and then those just making that same type of cell over and over again? Or is this something that the embryo's own DNA tells them to do with no outside influence?

The answer is simple. DNA isn't the blueprint for making proteins. The DNA isn't deciding which proteins to make at all. It's the cellular and extracellular enivironment, genomic imprinting, context, history of the cell etc.

Now you can reformulate your question.

If DNA is the blueprint for making proteins which are used to make the cells, then how does DNA "know" which proteins to make for the certain type of cell (bone, skin, muscle, etc.) it is creating? Is this started by the reproductive organs of the parent telling embryonic stem cells what to do in the beginning, and then those just making that same type of cell over and over again? Or is this something that the embryo's own DNA tells them to do with no outside influence?

Wow. A big question with a big answer. In short: differential gene expression. Certain transcription factors are provided in the egg, 'ready-to-go', for the zygote's use. The transcription factors bind at specific sites in the zygote's genome and regulate the expression of particular genes. Some of those genes in turn will encode further transcription factors. Through asymmetric cell division, it is possible to produce two daughter cells with different concentrations of a given transcription factor and therefore with different cellular fates. Stem cells divide in turn to yield daughter cells with different fates across different lineages.

A good example of a maternal effect gene in the fruit fly Drosophila is Bicoid, which you can read more about here
http://scienceblogs.com/pharyngula/2...s_and_morp.php

and here

http://en.wikipedia.org/wiki/Bicoid#...l_effect_genes

More on asymmetric cell division can be found at

http://en.wikipedia.org/wiki/Asymmetric_cell_division

and on Differentiation at

http://en.wikipedia.org/wiki/Cellular_differentiation

I would strongly advise you to thoroughly read a Gene Expression textbook e.g. Lewin B.'s 'Genes' - i forget what Edition it is upto now. Probably X. It is an excellent and enlightening read. In fact, I would advise reading a Developmental Biology textbook, as well.

Best wishes,

Tridimity. :wink:

First of all , the analogy of a blueprint for DNA is not a good one. For example , while a blueprint for a building can be reversed into the actual finished building and vice-versa , an individual’s DNA cannot be reversed to determine the actual body of the individual. Therefore a blueprint is reversible , DNA is not.

First , there is the single fertilised egg. This then divides to make two cells , and then redoubles into four and so on. Consider them as successive generations.

The process is best explained by taking just one cell before and after division (during embryonic development):
The two halves of the cell before division were ---to keep things simple---chemically different so that as they divided (though identical in their genes) different genes were turned on or off due to the chemical dissimilarity between the two sides (through methylation or demethylation of genes). The expression of genes then initiates the process of transcription and translation to produce proteins. Given that the gene expression in the two cells are different, the protein products of the two cells will also be different which explains the differences between different cell types , both in their function and their phenotype.

As such , every single cell in the human body is derived from a single fertilised egg. Cells come to differ in different parts of the body , even though they are genetically identical , because of their history of asymmetric cell division during the short course of embryonic development.

Thanks, I have been trying to get an answer that I can actually understand, but none of the places I've looked at so far have given me any information in plain english. I guess I wasn't looking in the right places.

every cell starts the same then microenvironment decides which cell becomes what.