lymphocytes and hepatocytes are the same!? - (Jul/15/2006 )
All human cells contain 23 pairs of genes that code for all the proteins that are necessary for human. If that is the case, that means all the cells are potentially able to produce all the proteins regardless what kind of cells they are (eg lymphocytes or hepatocytes). So, what exactly is the machanism which differs the proteins produced by lymphocytes and hepatocytes for example?
A gene means more than just the coding sequence for a particular amino acid sequence of a particular protein, it also contains so called regulatory sequences. The regulatory sequences contain information that can be used by cells to control the timing and the rate (or frequency) of the usage of the coding sequences. In other words, at a given time, cells can determine when and how much a particular gene will be turned on to make a particular protein for a particular amount. This is achieved by a group of protein transcriptional factors that capable of binding to regulatory sequences of genes.
All humans are originated from a single cell in fertilized egg. During embryonic development, cells multiply and differentiate into many specialized cell types, each have their own set of transcriptional factors. This allows cells to maintain a unique gene expression pattern that is not shared with other cell type. Therefore hepatocytes make proteins special to hepatocytes and lymphocytes make protein unique to lymphocytes.
It is just a tip of an iceberg of how cells control their gene expression pattern. Did I addressed your question?
Any human cell contains 23 pairs of chromosomes (exept for the egg and semen cells, they contain 23 chromosomes, 1 of each pair), and on these chromosoms, some 30.000 genes (last figure I heard estimated arount 30.000, could be more or less) are endoded. (Not to be an ass, but to make this conversation a bit more correct).
Thank you genehunter. Now i have a better idea on what is happening inside the gene. Thanks vairus for correcting the mistake. That is a serious mistake.
I tried not to overly complicate this issue, but if you add all gene sequences up (regulatory+ coding sequences), that only accounts for ~5-10% of the total genomic sequence. Scientists are working hard to find out what the rest of the sequence function are.