Protein The structure of a prokaryotic operon of protein-coding genes. Regulatory sequence controls when expression occurs for the multiple protein coding regions red.
Garland Science ; Search term An Overview of Gene Control The different cell types in a multicellular organism differ dramatically in both structure and function. If we compare a mammalian neuron with a lymphocytefor example, the differences are so extreme that it is difficult to imagine that the two cells contain the same genome Figure For this reason, and because cell differentiation is often irreversible, biologists originally suspected that genes might be selectively lost when a cell differentiates.
Figure A mammalian neuron and a lymphocyte. The long branches of this neuron from the retina enable it to receive electrical signals from many cells and carry those signals to many neighboring cells. The lymphocyte is a white blood cell involved in the immune more They generally do this without altering the sequence of their DNA.
Evidence for the preservation of the genome during cell differentiation comes from a classic set of experiments in frogs. When the nucleus of a fully differentiated frog cell is injected into a frog egg whose nucleus has been removed, the injected donor nucleus is capable of directing the recipient egg to produce a normal tadpole Figure A.
Because the tadpole contains a Overview of gene types range of differentiated cells that derived their DNA sequences from the nucleus of the original donor cell, it follows that the differentiated donor cell cannot have lost any important DNA sequences.
A similar conclusion has been reached in experiments performed with various plants. Here differentiated pieces of plant tissue are placed in culture and then dissociated into single cells.
Often, one of these individual cells can regenerate an entire adult plant Figure B. Finally, this same principle has been recently demonstrated in mammals, including sheep, cattle, pigs, goats, and mice by introducing nuclei from somatic cells into enucleated eggs; when placed into surrogate mothers, some of these eggs called reconstructed zygotes develop into healthy animals Figure C.
Figure Evidence that a differentiated cell contains all the genetic instructions necessary to direct the formation of a complete organism. A The nucleus of a skin cell from an adult frog transplanted into an enucleated egg can give rise to an entire tadpole.
Further evidence that large blocks of DNA are not lost or rearranged during vertebrate development comes from comparing the detailed banding patterns detectable in condensed chromosomes at mitosis see Figure By this criterion the chromosome sets of all differentiated cells in the human body appear to be identical.
Moreover, comparisons of the genomes of different cells based on recombinant DNA technology have shown, as a general rule, that the changes in gene expression that underlie the development of multicellular organisms are not accompanied by changes in the DNA sequences of the corresponding genes.
There are, however, a few cases where DNA rearrangements of the genome take place during the development of an organism—most notably, in generating the diversity of the immune system of mammals discussed in Chapter Different Cell Types Synthesize Different Sets of Proteins As a first step in understanding cell differentiationwe would like to know how many differences there are between any one cell type and another.
Although we still do not know the answer to this fundamental question, we can make certain general statements. Many processes are common to all cells, and any two cells in a single organism therefore have many proteins in common.
These include the structural proteins of chromosomes, RNA polymerases, DNA repair enzymes, ribosomal proteins, enzymes involved in the central reactions of metabolismand many of the proteins that form the cytoskeleton.
Some proteins are abundant in the specialized cells in which they function and cannot be detected elsewhere, even by sensitive tests. Hemoglobin, for example, can be detected only in red blood cells.
Studies of the number of different mRNAs suggest that, at any one time, a typical human cell expresses approximately 10,—20, of its approximately 30, genes.
When the patterns of mRNAs in a series of different human cell lines are compared, it is found that the level of expression of almost every active gene varies from one cell type to another. A few of these differences are striking, like that of hemoglobin noted above but most are much more subtle.
The patterns of mRNA abundance determined using DNA microarrays, discussed in Chapter 8 are so characteristic of cell type that they can be used to type human cancer cells of uncertain tissue origin Figure Although the differences in mRNAs among specialized cell types are striking, they nonetheless underestimate the full range of differences in the pattern of protein production.
As we shall see in this chapter, there are many steps after transcription at which gene expression can be regulated. In addition, alternative splicing can produce a whole family of proteins from a single gene.As the highest-ranked open access journal in its field, Genome Biology publishes outstanding research that advances the fields of biology and biomedicine from a genomic and post-genomic perspective.
Our responsive international editors provide excellent service and communication to authors throughout the entire publishing experience. How different genes are expressed in different cell types.
The big picture of eukaryotic gene regulation. Apr 03, · Hemochromatosis is the abnormal accumulation of iron in parenchymal organs, leading to organ toxicity. This is the most common inherited liver disease in white persons and the most common autosomal recessive genetic disorder.
Adult non-Hodgkin lymphoma is a disease in which malignant (cancer) cells form in the lymph system. The major types of lymphoma are Hodgkin lymphoma and non-Hodgkin lymphoma.
These different patterns of gene expression cause your various cell types to have different sets of proteins, making each cell type uniquely specialized to do its job. For example, one of the jobs of the liver is to remove toxic substances like alcohol from the bloodstream. The Medical Biochemistry Page is a portal for the understanding of biochemical, metabolic, and physiological processes with an emphasis on medical relevance.