Coding DNA

Coding DNA, functional genes

Each chromosome contains one continuous DNA strand. If DNA from the different chromosomes is added, the human genome contains roughly 3.2 billion DNA base pairs and each normal cell nucleus, which has a double set of chromosomes, nearly 7 billion base pairs (7.3 x 10 -12 g DNA). The coding DNA, we mean those parts of the base sequence that plays a messenger (mRNA), which serves as a recipe to a poli peptide or other RNA molecules that have specific functions in the cell (tRNA, rRNA).

At the completion of human genome project in April 2002, where 99.9% of the base sequence of all chromosomes the DNA strands were determined, the following was prepared: humans have only 30 000-35 000 protein structural genes (much like the mouse), equal to 1, 5% of the total DNA sequence. Additional 2.5% of DNA has a different practical significance known. At least, 95% of human DNA sequence is copied from cell to daughter cell and from generation to generation, has no known functional significance - except probably for the hybrids between chromosomes. This intergenic DNA consists mainly of various types of tandem repeated DNA sequences (see below) interspersed with "false" genes (pseudo-genes, sequences that are partially similar to functional genes but are missing parts, so they can be used / played into RNA). The coding DNA sequence of a polypeptide is in the chromosomes of the rule divided up into multiple pieces (exons) with non-coding sections between (introns), so the gene extent in the chromosome's DNA (genomic DNA) can be much larger than the coding part. All first depreciated to a messenger (pre-mRNA), which as the nucleus gets cut out, the non-coding parts of a splicing process before the final messenger (mRNA) is out of the nucleus and serve as a model for amino acid sequence of the protein.
functional genes

Changes, mutations, which set a gene more or less out of function, can thus be in the coding exons, in introns as splice not be wrong (even exons spliced ​​out) or there is a reading frame error, or sit in the regulatory elements in which the gene is activated. When an artificial copy of mRNA return code of a complementary cDNA, one can create a contiguous coding gene. On and turning off the genes is done by the influence of sequences that lies ahead for the protein part. To prove that you have obtained a functional gene can thus be tested against "gene libraries" from the cDNA. Ahead of many functional genes are often a repetition of two base pairs, the so-called CpG islands.

One of the big surprises in recent years is the discovery that genes in certain chromosomal regions are not functioning the alike way if they inherited from the father or mother. Prior to fertilization affected the same gene variant (allele) differs during sperm formation and during egg formation by a chemical modification (methylation) in a manner that follows allele through cell divisions. The phenomenon is called imprinting (embossing). This is the reason that the identicle chromosome damage to the chromosome 15 inherited from the father may not be uncommon Prader-Willy obesity syndrome (the plant from the father is gone. The plants from the mother are imprinted and functions not), while the same chromosome damage is inherited from the mother makes a very another syndrome, Angelman's happy puppet syndrome (plant from the mother is missing; Angelman gene from the father is imprinted). This unexpected gender difference could conceivably be the cause of that "cloning" of mammals could not be done technically, no pets; however, researchers have demonstrated possible technical fix, when after fertilization replaced the cell nuclei. (Cloning of higher animals adopted banned at a speed in Parliament in March 1997.)