How do cells become specialized?

All cells in our body contain the same genetic information stored in the DNA chromosomes located in the nucleus. So how do cells become skin cells, liver cells etc.? Cells undergo a process called differential gene expression. This process allows cells to become specialized, as their structure determines their function. The process begins when a stimulus acts on an unspecialized cell (a cell that has the potential to become any cell in the body- multipotent stem cells). This stimulus causes some genes in the DNA to become inactive. This means that they are basically present in the genome, but are 'switched off'. The genes that remain active (ie. 'switched on'), are able to be transcribed, to produce RNA. This mRNA (messenger RNA) that is produced, leaves the nucleus and enters the cytoplasm, where it attaches on a free ribosome or on a ribosome located on the endoplasmic reticulum (rER). Following transcription, where a particular section of the DNA is copied into a new molecule RNA to be transported, comes translation. Translation is the process of 'reading' this information, in order to produce the specific polypeptide that the gene encodes. Transcription and translation occur repeatedly until all of the active genes on the cell are encoded, producing different proteins. Proteins are polypeptide chains made from amino acids, that are able to alter the structure of the cell. Some proteins produced are enzymes, that have different roles in the cell. An example of a type of enzyme is protease- an enzyme that helps in the digestion (breaking down into simpler monomers) of a protein. Since these proteins can alter the structure of the cell in different ways, they are able to determine its function. To summarise: Unspecialized cells become specialised by external stimuli that alter gene expression- turn some genes on and some off. Following transcription and production of the mRNA, translation produces proteins that are able to determine the cell's structure hence function.