Clemencia

Páginas: 5 (1021 palabras) Publicado: 21 de marzo de 2010
DNA genetic material of all cellular organisms and most viruses. DNA carries the information needed to direct protein synthesis and replication. It is called protein synthesis to the production of proteins needed by the cell or virus for its activities and develop. Replication is the set of reactions by which DNA copies itself every time a cell or a virus is reproduced and transmitted tooffspring the information it contains. In almost all organisms cellular DNA is organized in the form of chromosomes in the cell nucleus.DNA genetic material of all cellular organisms and most viruses. DNA carries the information needed to direct protein synthesis and replication. It is called protein synthesis to the production of proteins needed by the cell or virus for its activities and develop.Replication is the set of reactions by which DNA copies itself every time a cell or a virus is reproduced and transmitted to offspring the information it contains. In almost all organisms cellular DNA is organized in the form of chromosomes in the cell nucleus.

Each DNA molecule consists of two strings or bands formed by a large number of chemical compounds called nucleotides. These chains form asort of twisted ladder is called a double helix.

Nucleotides from each of the two chains that form the DNA establishes a specific association with the corresponding chain of the other. Due to the chemical affinity between the bases, nucleotides containing Adenia always fit with the ends and containing containing containing cytosine with guanine. The complementary bases are joined together byweak chemical bonds called hydrogen bonds.

The DNA molecule has a ladder structure consisting of sugars, phosphates and four nucleotide bases called Adenia, thymine, cytosine and guanine. The genetic code is determined by the order of these bases, and each gene has a unique sequence of base pairs. Scientists use these sequences to locate the position of genes on chromosomes and to map thehuman genome.

In 1953, the American biochemist James Watson and British biophysicist Francis Crick published the first description of the structure of DNA. His model became so important to understand protein synthesis, DNA replication and mutation, which scientists in 1962 won the Nobel Prize in Medicine for their work.

DNA includes instructions for protein production. A protein is acompound formed by small molecules called amino acids that determine its structure and function. The amino acid sequence is in turn determined by the sequence of nucleotide bases in DNA. Each sequence of three bases, called triplet, is a word of the genetic code or codon, which specifies a particular amino acid. Thus, the triplet GAC (guanine, adenine, cytosine) is the codon for the amino acidleucine, while the CAG (cytosine, adenine, guanine) is the amino acid valine. Therefore, a protein consisting of 100 amino acids is encoded by a 300 nucleotide segment of DNA. Of the two polynucleotide chains that form a DNA molecule, only one, called parallel, it contains the information necessary for the production of an amino acid sequence determined. The other, called antiparalela helpsreplication.

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Protein synthesis begins with the separation of DNA on both strands. In a process called transcription, a part of the parallel strand acts as template to form a new chain is called messenger RNA or mRNA (see ribonucleic acid). The mRNA leaves the cell nucleus and attaches to the ribosomes, specialized cellular structures that serve as the center of protein synthesis. Amino acidsare transported to the ribosomes by another type called transfer RNA (tRNA). Starts a phenomenon called translation which is the link of amino acids in a sequence determined by the mRNA to form a protein molecule.

In almost all cellular organisms, replication of DNA molecules occurs in the nucleus, just before cell division. It starts with the separation of the two polynucleotide chains,...
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