📢 The DNA Genes And The Genetic Code

The instructions that determine all the characteristics and functions of an organism are found in its genetic material: DNA (deoxyribonucleic acid).

The knowledge of DNA, its structure and function, was decisive for the development of modern biotechnology.

The double helix structure of DNA, proposed by researchers James Watson and Francis Crick in 1953, provided answers to many questions about inheritance. He predicted the self-replication of the genetic material and the idea that the genetic information was contained in the sequence of the bases that make up the DNA. Moreover, over the years and investigations, it was determined that all living beings contain a similar DNA, formed from the same units: nucleotides. This genetic code by which cell instructions are "written" is common to all organisms. That is, the DNA of a human being can be "read" into a bacterium, and a plant can interpret the genetic information of a different plant. This property of genetic information is known as "universality of the genetic code".

The universal genetic code is one of the basic concepts to understand the processes of modern biotechnology. For example, the possibility of generating transgenic organisms, and that the instructions of the DNA of an organism can determine new characteristics in totally different organisms.

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The structure of DNA

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DNA is organized into chromosomes. In eukaryotic cells chromosomes are linear, while prokaryotic organisms, such as bacteria, have circular chromosomes. For each species, the number of chromosomes is fixed. For example, humans have 46 chromosomes in each somatic cell (non-sexual), grouped in 23 pairs, of which 22 are autosomes and one pair is sexual. A woman will have a pair of XX sex chromosomes and a male will have an XY pair.

Each chromosome has two arms, located above and below the centromere. When chromosomes are duplicated, prior to cell division, each chromosome is made up of two DNA molecules linked by the centromere, known as sister chromatids.

DNA is made up of two chains, each made up of nucleotides. Each nucleotide, in turn, is composed of a sugar (deoxyribose), a phosphate group and a nitrogenous base. The nitrogenous bases are four: adenine (A), thymine (T), cytosine (C), and guanine (G), and always an A faces a T and a C faces a G in the double chain. The opposing bases are said to be complementary. The DNA adopts a double helix shape, like a spiral staircase where the sides are chains of sugars and phosphates connected by "steps", which are the nitrogenous bases. The DNA molecule is associated with proteins, called histones, and is very coiled and compacted to form the chromosome.

The double helix of DNA with complementary nitrogenous bases that are located inward and establish non-covalent bonds (or attractive forces) with each other that maintain the structure of the molecule. Deoxyribose (sugars) and phosphate groups constitute the columns of the molecule.

How are instructions written in the DNA interpreted?

The information is stored in the DNA in the sequence code of bases A, T, C and G that combine to originate "words" called genes. Genes are fragments of DNA whose nucleotide sequence codes for a protein. In other words, a particular type of protein is manufactured (synthesized) from the information "written" in that DNA fragment. Although, in fact, genes also carry the information necessary to make RNA molecules (ribosomal and transfer) that are involved in the process of protein synthesis. RNA (ribonucleic acid) is a molecule with a structure similar to DNA.

A gene is not a structure that is seen but is defined at a functional level. It is a sequence that will start somewhere in the DNA and will end in another. To know a gene is sequenced, the amount of nucleotides that form it and the order in which they are located are determined.

All the cells of an organism have the same genome, or set of genes. But, in each cell the genes that are used are expressed. For example, although a skin cell has all the genetic information just like the liver cell, only those genes that give skin characteristics will be expressed on the skin, while genes that give liver characteristics will be there "off" " In contrast, genes that give "liver" traits will be active in the liver and inactive in the skin. What is not used is mostly compacted. This packaging can be temporary or definitive.

The synthesis of proteins

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Proteins are macromolecules that fulfill varied functions. There are structural proteins, others are enzymes, others transport oxygen such as hemoglobin, there are proteins involved in the immune defense, such as antibodies, others fulfill functions of hormones such as insulin, etc.

Just as DNA is composed of nucleotides, proteins are composed of amino acids. There are 20 different amino acids, and each protein has a particular amino acid sequence.

The process of protein synthesis basically consists of two stages: transcription and translation. In the first stage, the "words" (genes) written in the DNA in the language of the nucleotides are copied or transcribed to another molecule, the messenger RNA (mRNA). Then, in the next stage, the mRNA is translated into the language of the proteins, that of the amino acids. This flow of information is known as the "central dogma of biology."

En ocasiones, la placa esternal se aplica a personas con alto riesgo, como aquellas que han tenido múltiples cirugías o personas de edad avanzada. La placa esternal es cuando el esternón se vuelve a unir con pequeñas placas de titanio después de la cirugía.

The transcript

During transcription, the RNA polymerase enzyme copies the sequence of a strand of DNA and makes an RNA molecule complementary to the transcribed DNA fragment. The process is similar to DNA replication, but the new molecule that forms is single-stranded and is called RNA. It is called messenger RNA because it will carry the information of the DNA to the ribosomes, the organelles responsible for making the proteins. RNA, or ribonucleic acid, is similar to DNA but not the same. RNA differs from DNA in that it is single chain, instead of deoxyribose sugar it has ribose, and instead of the nitrogenous base thymine, (T), it has uracil (U).

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The translation and the genetic code

The messenger RNA molecule is transferred to the ribosomes where the translation stage occurs. During this stage the ribosome reads the nucleotide sequence of the messenger RNA by triplets or triplets of nucleotides, called codons. As the ribosome reads the codon sequence it forms a protein, starting from the union of amino acids. According to which codon the ribosome "reads" is placing the corresponding amino acid. If the combination of four bases taken from three is considered, there is a total of 64 possible codons. Each codon determines which amino acid will be placed in the protein being manufactured. Of the 64 codons, 61 correspond to amino acids and 3 are stop codons, responsible for the finalization of protein synthesis.

The genetic code or "dictionary" allows to translate the information written in the language of nucleic acids (nucleotides) to the language of proteins (amino acids), and is universal, that is, it is valid for all living beings.

Thus, the ATG sequence (AUG in the mRNA) codes for the amino acid methionine, and the TTT codon (UUU in the mRNA) codes for the amino acid phenylalanine in all living organisms. As there are only 20 amino acids in nature, several codons can code for the same amino acid (for example, the amino acid glycine corresponds to the codons GGU, GGC, GGA and GGG).

Each codon of the mRNA is read by another RNA, called transfer RNA (tRNA), which acts as an "adapter" between the information that the mRNA carries and the amino acids that must be placed to form the corresponding protein. The tRNA is very small compared to mRNAs and has a sequence, called anticodon that pairs (that is, is complementary) with the codon. Each transfer RNA has an anticodon and "charges" a particular amino acid. For example, the tRNA that has the anticodon UCA, matches the codon AGU, and charges the amino acid serine (Ser). In the same way, the tRNA that charges tyrosine (Tyr) is paired, through its anticodon, with the UAC codon. Thus a polypeptide chain (protein) is formed as the anticodons of the tRNAs recognize their respective codons in the mRNA. This process of protein synthesis occurs in ribosomes.

DNA and modern biotechnology

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When the scientists understood the structure of the genes and how the information they carried was translated into functions or characteristics, they began to look for ways to isolate, analyze, modify and even transfer them from one organism to another to confer a new characteristic. Exactly, that is what genetic engineering is all about, which we could define as a set of methodologies that allows us to transfer genes from one organism to another, and that gave impetus to modern biotechnology. Genetic engineering allows you to clone (multiply) DNA fragments and express genes (produce the proteins for which these genes encode) in organisms other than the source. Thus, it is possible to obtain proteins of interest in organisms different from the original from which the gene was extracted, improve crops and animals, produce drugs, and obtain proteins that use different industries in their manufacturing processes.