10.6.1. The genetic code

The genetic code

The genetic code is the set of rules that allows the translation of a sequence of nucleotides of the mRNA to a sequence of amino acids constituting a protein, in all living beings, which shows that has a single or universal origin, the least the context of our planet.

The code defines the relationship between sequences of three nucleotides, called codons, and amino acids. Thus, each codon corresponds to a specific amino acid.

The sequence of genetic material is made up of four different nitrogenous bases, which have a function equivalent to letters in the genetic code : adenine (A), thymine (T), guanine (G) and cytosine (C) in DNA and adenine ( A), uracil (U), guanine (G), and cytosine (C) in RNA.

The translation of the genetic message into proteins can be done thanks to this "dictionary" called the genetic code . Although there are only 20 different amino acids to code for, only 4 different nitrogenous bases are available to do so. Therefore, it will take more than one nitrogen base to code for each amino acid. If they were two nitrogenous bases, they would encode 4² = 16 different pairs of bases that would encode 16 different amino acids. And if they were three different bases (a triplet), they would code, 4³ = 64 different triplets, which could be used to code even more than the 20 amino acids that exist.

Because of this, the number of possible codons is 64:

61 codons encode amino acids (one of them being the start codon, AUG, and encoding the amino acid methionine ).
3 codons that do not code for any amino acids, but are stop signals (UAA, UAG, and UGA).

Each triplet (group of three) nucleotides of mRNA is called a codon. The codon sequence determines the amino acid sequence in a specific protein, which will have a specific structure and function. The DNA triplets that have been transcribed to these codons are called coding.

By Andrés Samael Cortina Ramírez [Public domain], via Wikimedia Commons

Código genético

Código genético | El código genético. Combinaciones de 4 b… | Flickr. (s. f.). Recuperado 28 de enero de 2017, a partir de https://www.flickr.com/photos/97815254@N06/28502326620/in/photostream/

Application: Genetic code.

By Madprime (Own work) [CC0, GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons

Characteristics of the genetic code

The genetic code has the following characteristics:

It is universal. The genetic code is shared by all known organisms, including viruses and organelles. Thus, for example, the codon UUU encodes the amino acid phenylalanine in both prokaryotes and eukaryotes. This indicates that the genetic code has had a unique origin in all known living beings. The word "universal" refers only to life on Earth, as life on another planet has not been proven.

Although we say it is universal, it has some exceptions, such as in mitochondria, protozoa and mycoplasmas (a type of bacteria), whose genetic code has some slight difference.

The genetic code is degenerate. It means that an amino acid is encoded by more than one codon. For example, although the codons GAA and GAG specify glutamic acid (redundancy), neither specifies another amino acid (there is no ambiguity). All amino acids, except methionine and tryptophan, are encoded by more than one codon (synonymous codons).

This can be an advantage, since if a nucleotide is changed by mistake, it may not encode a different amino acid and another protein is generated.

It does not present imperfection. There is no ambiguity, no codon can code for more than one amino acid, since if it did, it would be a big problem for the same gene to code for different proteins.
It is a code without overlaps. The triplets are arranged in a linear and continuous manner, without spaces between them and without sharing any nitrogen base. Its reading is done in a single direction (5'→3'), from the initiation codon, which indicates the beginning of the protein, to the stop codon that indicates its end. However, the same mRNA can have several start codons, which means that several different polypeptides could be synthesized from the same mRNA.

Interactive activity: Exercises on the genetic code.

Basic ideas about the genetic code

The genetic code

The genetic code has these characteristics:

It is universal. All known beings share the same genetic code.
It is degenerate. The same amino acid is encoded by more than one codon.
It does not present imperfection. The genetic code is not ambiguous, a codon cannot code for more than one amino acid.
No overlaps. The triplets are arranged in a linear and continuous way and are read in the 5'→3' direction.

Licensed under the Creative Commons Attribution Share Alike License 4.0

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Skip navigation Biology 2nd Baccalaureate Biology 2nd Bac. 1. Bioelements and biomolecules. Water and mineral salts 1.1. Chemical bonds in biology 1.1.1. Intramolecular bonds 1.1.1.1. Covalent bond 1.1.1.2. Ionic bond 1.1.2. Intermolecular bonds 1.1.2.1. Van der Waals forces 1.1.2.2. Hydrogen bonds 1.2. The chemical basis of life: inorganic and organic components 1.2.1. Primary bioelements 1.2.2. Secondary bioelements 1.2.3. Trace elements 1.3. The immediate principles or biomolecules 1.3.1. Water 1.3.1.1. Chemical structure of water 1.3.1.2. Properties and functions of water 1.3.2. Mineral salts 1.3.2.1. Functions of salts in solution 1.3.2.2. Colloidal solutions and dispersions 1.3.2.3. Properties of colloidal dispersions 1.3.2.4. Diffusion, osmosis and dialysis 1.3.2.4.1. Diffusion 1.3.2.4.2. Osmosis 1.3.2.4.3. Dialysis 1.4. Bibliography 2. Glucides 2.1. Glucid concept 2.2. Classification of carbohydrates 2.3. Monosaccharides 2.3.1. Trioses 2.3.1.1. Spatial isomerism or stereoisomerism 2.3.2. Tetroses 2.3.3. Pentoses 2.3.3.1. Monosaccharide cyclization 2.3.4. Hexoses 2.4. The N-glucosidic and O-glucosidic bonds 2.4.1. Substances derived from monosaccharides 2.5. Disaccharides 2.6. Polysaccharides 2.6.1. Homopolysaccharides 2.6.1.1. Reserve homopolysaccharides 2.6.1.2. Structural homopolysaccharides 2.6.2. Heteropolysaccharides 2.6.3. Heterosides 2.7. General functions of glucides 2.8. Bibliography 3. Lipids 3.1. Lipid concept 3.2. Classification of lipids 3.2.1. Fatty acids 3.2.1.1. Saturated and unsaturated fatty acids 3.2.1.2. Chemical properties of fatty acids 3.2.1.3. Physical properties of fatty acids 3.2.1.4. Fatty Acid Functions 3.2.2. Saponifiable lipids or with fatty acids 3.2.2.1. Simple lipids 3.2.2.1.1. Acylglycerides 3.2.2.1.2. Cerides 3.2.2.2. Complex lipids 3.2.2.2.1. Phospholipids 3.2.2.2.2. Glycolipids 3.2.3. Unsaponifiable lipids or without fatty acids 3.3. Lipid functions 3.4. Bibliography 4. Proteins 4.1. Introduction to proteins 4.2. Amino acids 4.2.1. Classification of amino acids 4.2.2. Properties of amino acids 4.3. The peptide bond 4.4. Protein 4.4.1. Protein structure 4.4.1.1. Primary structure of proteins 4.4.1.2. Secondary structure of proteins 4.4.1.3. Tertiary structure of proteins 4.4.1.4. Quaternary structure of proteins 4.4.2. Protein properties 4.4.3. Classification of proteins 4.4.3.1. Holoproteins 4.4.3.2. Heteroproteins 4.4.4. Protein functions 4.5. Enzymes 4.5.1. Structure of enzymes 4.5.2. The active center of enzymes 4.5.3. General Mechanism of Enzyme Catalysis 4.5.4. Regulation of enzyme activity 4.5.5. Allosteric enzymes 4.5.6. Nomenclature and classification of enzymes 4.6. The vitamins 4.6.1. Fat-soluble vitamins 4.6.2. Water soluble vitamins 4.7. Bibliography 5. Nucleotides and nucleic acids 5.1. The chemical composition of nucleic acids 5.1.1. Components of nucleic acids 5.1.2. Concept, types and functions of nucleic acids 5.1.3. Nucleosides 5.1.4. Nucleotides 5.1.4.1. Nucleotide functions 5.1.5. Nucleic acids 5.2. Deoxyribonucleic acid (DNA) 5.2.1. DNA structure 5.2.1.1. Primary structure of DNA 5.2.1.2. Secondary structure of DNA 5.2.1.3. Tertiary structure of DNA 5.2.1.3.1. Tertiary structure of DNA in prokaryotes 5.2.1.3.2. Tertiary structure of DNA in eukaryotes 5.2.1.4. Quaternary structure of DNA 5.2.2. DNA types 5.2.3. Genetic material: chromatin and chromosomes 5.2.3.1. Karyotype and karyogram 5.3. Ribonucleic acid (RNA) 5.3.1. RNA types 5.3.1.1. Transfer RNA 5.3.1.2. Messenger RNA 5.3.1.3. Ribosomal RNA 5.3.1.4. Nucleolar RNA 5.3.1.5. Small nuclear RNA 5.3.2. Functions of ribonucleic acids 5.4. Bibliography 6. Cell morphology 6.1. Cell concept 6.1.1. Cell history 6.1.2. Cell theory 6.2. Levels of cellular organization 6.2.1. General characteristics of cells 6.2.2. Prokaryotic cells 6.2.2.1. Prokaryotic cell morphology 6.2.2.2. Structure of prokaryotes 6.2.2.2.1. Bacterial capsule 6.2.2.2.2. Bacterial wall 6.2.2.2.3. Plasma membrane 6.2.2.2.4. Cytoplasm-Ribosomes-Inclusions 6.2.2.2.5. Bacterial DNA 6.2.2.2.6. Bacterial appendages 6.2.2.3. Bacteria Physiology 6.2.3. Eukaryotic cells 6.2.3.1. Animal and plant cell 6.2.3.1.1. Animal eukaryotic cell 6.2.3.1.2. Plant eukaryotic cell 6.2.3.2. Cell Evolution: Endosymbiont Theory 6.3. Size, shape and quantity 6.4. The plasma membrane 6.4.1. Chemical composition of the membrane 6.4.2. The structure of the membrane. The fluid mosaic model 6.4.3. Functions of the plasma membrane 6.4.4. Transport across the membrane 6.4.4.1. Small molecule transport 6.4.4.2. Macromolecule transport 6.4.5. Plasma membrane differentiations 6.5. The cell wall of plant cells 6.5.1. Chemical composition of the cell wall 6.5.2. Cell wall structure 6.5.3. Cell wall differentiations 6.5.4. Cell wall functions 6.6. Extracellular matrix or glucocalyx 6.7. Cytosol or hyaloplasm 6.8. The cytoskeleton 6.8.1. Microfilaments or actin filaments 6.8.2. Intermediate filaments 6.8.3. Microtubules 6.9. Cell membrane and organelle systems 6.9.1. Membrane systems 6.9.1.1. The endoplasmic reticulum 6.9.1.2. Golgi apparatus 6.9.2. Cell organelles 6.9.2.1. Lysosomes 6.9.2.2. Peroxisomes 6.9.2.3. Vacuoles 6.9.2.4. Mitochondria 6.9.2.4.1. Functions of the mitochondria 6.9.2.5. Plastids 6.9.2.5.1. Chloroplasts 6.9.2.6. Ribosomes 6.9.2.7. Centrosome 6.9.2.8. Cilia and flagella 6.10. Cell motility 6.11. The cell nucleus 6.11.1. Characteristics of the cell nucleus 6.11.2. The interphase nucleus 6.11.3. The mitotic nucleus or nucleus in division 6.12. Bibliography 7. Metabolism 7.1. Metabolism 7.1.1. Energetic Aspects of Cellular Chemical Reactions 7.2. Catabolism 7.2.1. Catabolism and obtaining energy 7.2.2. Carbohydrate catabolism 7.2.2.1. Glycolysis 7.2.2.2. Cellular respiration 7.2.2.2.1. Oxidative decarboxylation 7.2.2.2.2. Krebs cycle 7.2.2.2.3. Electron transport chain 7.2.2.2.4. Energy balance of cellular respiration 7.2.2.3. Fermentations 7.2.2.3.1. Alcoholic or ethyl fermentation 7.2.2.3.2. Lactic fermentation 7.2.2.3.3. Other types of fermentations 7.3. Anabolism 7.3.1. Autotrophic anabolism 7.3.2. Photosynthesis 7.3.2.1. Photochemical or light phase 7.3.2.1.1. Photosystems 7.3.2.1.2. Photophosphorylation 7.3.2.1.2.1. Non cyclic photophosphorylation 7.3.2.1.2.2. Cyclic photophosphorylation 7.3.2.2. Biosynthetic or dark phase 7.3.2.3. Factors influencing photosynthesis 7.3.2.4. Products of photosynthesis 7.3.3. Chemosynthesis 7.4. Bibliography 8. Cell reproduction 8.1. The cell cycle 8.1.1. Interphase 8.1.2. Cellular division 8.2. Cellular division 8.2.1. Mitosis 8.2.1.1. Prophase 8.2.1.2. Metaphase 8.2.1.3. Anaphase 8.2.1.4. Telophase 8.2.1.5. Cytokinesis 8.2.1.6. More on mitosis 8.2.2. Meiosis 8.2.2.1. Meiosis I 8.2.2.2. Meiosis II 8.2.3. Meiosis and sexual reproduction 8.2.4. Meiosis and life cycle 8.2.5. Biological importance of meiosis 8.3. Differences and similarities between mitosis and meiosis 8.4. Bibliography 9. Classical genetics 9.1. Genetics basics 9.2. Mendelian genetics 9.2.1. The method 9.2.2. Mendel's Laws 9.2.2.1. Mendel's first law or principle of uniformity in the first generation 9.2.2.2. Mendel's second law or principle of segregation 9.2.2.2.1. Backcross and test crossover 9.2.2.3. Mendel's third law or principle of independent combination 9.3. Gene interaction 9.3.1. Gene interaction between allelic genes 9.3.2. Gene interaction between non-allelic genes that influence for the same trait 9.4. Chromosomal theory of heredity 9.5. Ligation and recombination 9.6. Complex mendelism 9.6.1. Multiple allelism 9.6.1.1. Lethal genes 9.6.2. Pleiotropy 9.6.3. Expressiveness and genetic penetrance 9.7. Sex-linked inheritance 9.7.1. Y-linked inheritance 9.7.2. X-linked inheritance 9.8. Heredity influenced by sex 9.9. Bibliography 10. Molecular genetics 10.1. DNA as hereditary material 10.2. DNA replication 10.2.1. The need for DNA replication 10.2.2. First hypotheses about DNA duplication 10.2.3. Meselson and Stahl experiment 10.2.4. The sense of growth of the new strands 10.2.5. Mechanism of DNA replication 10.2.5.1. Replication in prokaryotes 10.2.5.2. Replication in eukaryotes 10.2.6. Error correction 10.2.7. Enzymes involved in replication 10.3. Gene concept 10.4. "One gene-one enzyme" theory 10.5. Transcription 10.5.1. Mechanism of transcription 10.5.1.1. Transcription in prokaryotes 10.5.1.2. Eukaryotic transcription 10.6. Translation or protein biosynthesis 10.6.1. The genetic code 10.6.2. Mechanism of translation of RNA to proteins 10.6.2.1. Translation in eukaryotes 10.7. Regulation of gene expression 10.8. Bibliography 11. Genetics and evolution 11.1. Mutations 11.2. Types of mutations 11.2.1. Gene or point mutation 11.2.2. Chromosomal or structural mutation 11.2.3. Mutation at the genomic level 11.3. Causes of mutations 11.4. Evolutionary implications of mutations 11.5. Metabolic implications of mutations 11.6. Bibliography 12. Microbiology and biotechnology 12.1. Microbiology 12.2. Viruses 12.2.1. Viral morphology 12.2.2. Viral physiology 12.2.2.1. Lytic cycle 12.2.2.2. Lysogenic cycle 12.2.2.3. Cycles of viruses of special interest 12.2.2.3.1. Flu virus life cycle 12.2.2.3.2. Life cycle of the AIDS virus 12.3. Other acellular forms 12.3.1. Viroids 12.3.2. Prions 12.4. Biotechnology 12.5. Bibliography 13. Immunology 13.1. Infection concept 13.2. Defense mechanisms against infections 13.2.1. Nonspecific mechanisms 13.2.1.1. Primary barriers: external defenses 13.2.1.2. Secondary barriers: internal defenses 13.2.2. Specific mechanisms 13.3. Immunity and immune system 13.3.1. Components of the immune system 13.3.2. Concept and nature of antigens 13.4. The immune response 13.4.1. Humoral immune response: the antibodies 13.4.1.1. Antibody-producing cells: B lymphocytes 13.4.1.2. Antibodies 13.4.1.2.1. Types of antibodies 13.4.1.2.2. Antigen-antibody reaction 13.4.1.3. Immune memory: primary and secondary responses 13.4.2. Cellular immune response: T lymphocytes 13.5. Types of immunity 13.5.1. Natural immunity 13.5.2. Artificial immunity 13.6. Immune system disorders 13.6.1. Autoimmunity 13.6.2. Hypersensitivity 13.6.3. Immunodeficiency 13.6.4. Transplants and the phenomenon of rejections 13.7. Bibliography « Previous \| Next » 10.6.1. The genetic code The genetic code The genetic code is the set of rules that allows the translation of a sequence of nucleotides of the mRNA to a sequence of amino acids constituting a protein, in all living beings, which shows that has a single or universal origin, the least the context of our planet. The code defines the relationship between sequences of three nucleotides, called codons, and amino acids. Thus, each codon corresponds to a specific amino acid. The sequence of genetic material is made up of four different nitrogenous bases, which have a function equivalent to letters in the genetic code : adenine (A), thymine (T), guanine (G) and cytosine (C) in DNA and adenine ( A), uracil (U), guanine (G), and cytosine (C) in RNA. The translation of the genetic message into proteins can be done thanks to this "dictionary" called the genetic code . Although there are only 20 different amino acids to code for, only 4 different nitrogenous bases are available to do so. Therefore, it will take more than one nitrogen base to code for each amino acid. If they were two nitrogenous bases, they would encode 4² = 16 different pairs of bases that would encode 16 different amino acids. And if they were three different bases (a triplet), they would code, 4³ = 64 different triplets, which could be used to code even more than the 20 amino acids that exist. Because of this, the number of possible codons is 64: 61 codons encode amino acids (one of them being the start codon, AUG, and encoding the amino acid methionine ). 3 codons that do not code for any amino acids, but are stop signals (UAA, UAG, and UGA). Each triplet (group of three) nucleotides of mRNA is called a codon. The codon sequence determines the amino acid sequence in a specific protein, which will have a specific structure and function. The DNA triplets that have been transcribed to these codons are called coding. By Andrés Samael Cortina Ramírez [Public domain], via Wikimedia Commons Código genético \| El código genético. Combinaciones de 4 b… \| Flickr. (s. f.). Recuperado 28 de enero de 2017, a partir de https://www.flickr.com/photos/97815254@N06/28502326620/in/photostream/ Application: Genetic code. By Madprime (Own work) [CC0, GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons Characteristics of the genetic code The genetic code has the following characteristics: It is universal. The genetic code is shared by all known organisms, including viruses and organelles. Thus, for example, the codon UUU encodes the amino acid phenylalanine in both prokaryotes and eukaryotes. This indicates that the genetic code has had a unique origin in all known living beings. The word "universal" refers only to life on Earth, as life on another planet has not been proven. Although we say it is universal, it has some exceptions, such as in mitochondria, protozoa and mycoplasmas (a type of bacteria), whose genetic code has some slight difference. The genetic code is degenerate. It means that an amino acid is encoded by more than one codon. For example, although the codons GAA and GAG specify glutamic acid (redundancy), neither specifies another amino acid (there is no ambiguity). All amino acids, except methionine and tryptophan, are encoded by more than one codon (synonymous codons). This can be an advantage, since if a nucleotide is changed by mistake, it may not encode a different amino acid and another protein is generated. It does not present imperfection. There is no ambiguity, no codon can code for more than one amino acid, since if it did, it would be a big problem for the same gene to code for different proteins. It is a code without overlaps. The triplets are arranged in a linear and continuous manner, without spaces between them and without sharing any nitrogen base. Its reading is done in a single direction (5'→3'), from the initiation codon, which indicates the beginning of the protein, to the stop codon that indicates its end. However, the same mRNA can have several start codons, which means that several different polypeptides could be synthesized from the same mRNA. Interactive activity: Exercises on the genetic code. Basic ideas about the genetic code The genetic code The genetic code has these characteristics: It is universal. All known beings share the same genetic code. It is degenerate. The same amino acid is encoded by more than one codon. It does not present imperfection. The genetic code is not ambiguous, a codon cannot code for more than one amino acid. No overlaps. The triplets are arranged in a linear and continuous way and are read in the 5'→3' direction. Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » These pages are semi-automatically translated from the web Biology 2nd Baccalaureate. Biología de 2º de Bachillerato (biologia-geologia.com). You can make any suggestion, question, comment, ..., in our forum 2º Bachillerato Biología - Foro de biologia-geologia.com
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The genetic code

Characteristics of the genetic code