Genetics basics, Exons, Introns, RNA polymerase II, DNA, RNA transcripts, Transcription, mRNA, tRNA, aminoacids, Translation, Proteins, Ribosomes, Secretion, Adenine, Guanine, Cytosine, Codons


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	Structural proteins are key building blocks of all cells. Other proteins such as enzymes and signal peptides, including cytokines and certain hormones, govern the functions of cells. Proteins are polymers containing defined sequences of amino acids covalently linked by peptide bonds. The amino acid sequences of proteins are encoded by the genes of cells, and the function of a cell is therefore directed by the genes that are (or have been) active in that cell. Consequently, measurements of gene activities are important for understanding cell behavior both under normal and diseased conditions. The figure shows a simplified view of the processes leading from a gene (part of the DNA in the nucleus of a cell) to protein synthesized in the ribosomes of the cell cytoplasm, and in this case its secretion from the cell.

	The figure below details the specific sequence of 4 different nucleic acid bases in DNA: adenine (A), guanine (G), cytosine (C) and thymine (T). When this gene is activated, one of the DNA strands is transcribed into messenger RNA (mRNA), where a complementary sequence of the bases is formed: on mRNA, an A in the DNA strand is transcribed to uracil (U) (thymine is not found in mRNA), G is transcribed to C, C to G, and T to A (mid left). Each set of 3 bases on the mRNA codes for individual amino acids (mid), and the sequence of the bases thus determines the amino acid sequence of the protein. Hence, the information to synthesize this specific protein is contained in the coding region(s) of the gene, exon(s) (see figure above) The specific pairing of T to A to and C to G during transcription of the gene is shown below right.

	Quantitative measurements of thousands of genes at a given time can give important information about the molecular biology underlying many diseases that burden the individual and the society. Without doubt, this will lead to improved and novel methods for diagnosing and treating diseases. Until recently, it has been impractical to carry out a detailed investigation of the complex state of activity of many thousand genes at the same time. This, however, is now possible with the development of microarray technologies for simultaneous quantitative measurement of the activities of a large number of genes. DNA chip technology The first attempts to clone DNA were carried out in 1973. Today, a substantial number of all human genes are known. Within a few years, the human genome project, an international research effort, should lead to characterization and annotation of the entire human genome. A newly developed instrument for effective use of this enormous amount of information is the so-called GeneChip® analysis system based on DNA microchips. The construction of one type of DNA microarrays, the GeneChip®, takes advantage of the same technology that is used for the manufacture of computer microchips (photo lithography) combined with in vitro synthesis of small pieces of DNA (oligonucleotides). It is now possible to synthesize up to 400.000 different oligonucleotides on a single chip. The oligonucleotides are designed to detect mRNA from a large number of genes. The chip resembles a minute chessboard with up to 400.000 individual areas, each area containing many copies of the same oligonucleotide.